Modules/parsermodule.c

/*  parsermodule.c
 *
 *  Copyright 1995-1996 by Fred L. Drake, Jr. and Virginia Polytechnic
 *  Institute and State University, Blacksburg, Virginia, USA.
 *  Portions copyright 1991-1995 by Stichting Mathematisch Centrum,
 *  Amsterdam, The Netherlands.  Copying is permitted under the terms
 *  associated with the main Python distribution, with the additional
 *  restriction that this additional notice be included and maintained
 *  on all distributed copies.
 *
 *  This module serves to replace the original parser module written
 *  by Guido.  The functionality is not matched precisely, but the
 *  original may be implemented on top of this.  This is desirable
 *  since the source of the text to be parsed is now divorced from
 *  this interface.
 *
 *  Unlike the prior interface, the ability to give a parse tree
 *  produced by Python code as a tuple to the compiler is enabled by
 *  this module.  See the documentation for more details.
 *
 *  I've added some annotations that help with the lint code-checking
 *  program, but they're not complete by a long shot.  The real errors
 *  that lint detects are gone, but there are still warnings with
 *  Py_[X]DECREF() and Py_[X]INCREF() macros.  The lint annotations
 *  look like "NOTE(...)".
 */

#include "Python.h"                     /* general Python API             */
#include "graminit.h"                   /* symbols defined in the grammar */
#include "node.h"                       /* internal parser structure      */
#include "token.h"                      /* token definitions              */
                                        /* ISTERMINAL() / ISNONTERMINAL() */
#include "compile.h"                    /* PyNode_Compile()               */

#ifdef lint
#include <note.h>
#else
#define NOTE(x)
#endif

#ifdef macintosh
char *strdup(char *);
#endif

/*  String constants used to initialize module attributes.
 *
 */
static char*
parser_copyright_string
= "Copyright 1995-1996 by Virginia Polytechnic Institute & State\n\
University, Blacksburg, Virginia, USA, and Fred L. Drake, Jr., Reston,\n\
Virginia, USA.  Portions copyright 1991-1995 by Stichting Mathematisch\n\
Centrum, Amsterdam, The Netherlands.";


static char*
parser_doc_string
= "This is an interface to Python's internal parser.";

static char*
parser_version_string = "0.4";


typedef PyObject* (*SeqMaker) (int length);
typedef int (*SeqInserter) (PyObject* sequence,
                            int index,
                            PyObject* element);

/*  The function below is copyrigthed by Stichting Mathematisch Centrum.  The
 *  original copyright statement is included below, and continues to apply
 *  in full to the function immediately following.  All other material is
 *  original, copyrighted by Fred L. Drake, Jr. and Virginia Polytechnic
 *  Institute and State University.  Changes were made to comply with the
 *  new naming conventions.  Added arguments to provide support for creating
 *  lists as well as tuples, and optionally including the line numbers.
 */

/***********************************************************
Copyright 1991-1995 by Stichting Mathematisch Centrum, Amsterdam,
The Netherlands.

                        All Rights Reserved

Permission to use, copy, modify, and distribute this software and its
documentation for any purpose and without fee is hereby granted,
provided that the above copyright notice appear in all copies and that
both that copyright notice and this permission notice appear in
supporting documentation, and that the names of Stichting Mathematisch
Centrum or CWI or Corporation for National Research Initiatives or
CNRI not be used in advertising or publicity pertaining to
distribution of the software without specific, written prior
permission.

While CWI is the initial source for this software, a modified version
is made available by the Corporation for National Research Initiatives
(CNRI) at the Internet address ftp://ftp.python.org.

STICHTING MATHEMATISCH CENTRUM AND CNRI DISCLAIM ALL WARRANTIES WITH
REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL STICHTING MATHEMATISCH
CENTRUM OR CNRI BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL
DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
PERFORMANCE OF THIS SOFTWARE.

******************************************************************/

static PyObject*
node2tuple(node *n,                     /* node to convert               */
           SeqMaker mkseq,              /* create sequence               */
           SeqInserter addelem,         /* func. to add elem. in seq.    */
           int lineno)                  /* include line numbers?         */
{
    if (n == NULL) {
        Py_INCREF(Py_None);
        return (Py_None);
    }
    if (ISNONTERMINAL(TYPE(n))) {
        int i;
        PyObject *v;
        PyObject *w;

        v = mkseq(1 + NCH(n));
        if (v == NULL)
            return (v);
        w = PyInt_FromLong(TYPE(n));
        if (w == NULL) {
            Py_DECREF(v);
            return ((PyObject*) NULL);
        }
        (void) addelem(v, 0, w);
        for (i = 0; i < NCH(n); i++) {
            w = node2tuple(CHILD(n, i), mkseq, addelem, lineno);
            if (w == NULL) {
                Py_DECREF(v);
                return ((PyObject*) NULL);
            }
            (void) addelem(v, i+1, w);
        }
        return (v);
    }
    else if (ISTERMINAL(TYPE(n))) {
        PyObject *result = mkseq(2 + lineno);
        if (result != NULL) {
            (void) addelem(result, 0, PyInt_FromLong(TYPE(n)));
            (void) addelem(result, 1, PyString_FromString(STR(n)));
            if (lineno == 1)
                (void) addelem(result, 2, PyInt_FromLong(n->n_lineno));
        }
        return (result);
    }
    else {
        PyErr_SetString(PyExc_SystemError,
                        "unrecognized parse tree node type");
        return ((PyObject*) NULL);
    }
}
/*
 *  End of material copyrighted by Stichting Mathematisch Centrum.
 */



/*  There are two types of intermediate objects we're interested in:
 *  'eval' and 'exec' types.  These constants can be used in the ast_type
 *  field of the object type to identify which any given object represents.
 *  These should probably go in an external header to allow other extensions
 *  to use them, but then, we really should be using C++ too.  ;-)
 *
 *  The PyAST_FRAGMENT type is not currently supported.  Maybe not useful?
 *  Haven't decided yet.
 */

#define PyAST_EXPR      1
#define PyAST_SUITE     2
#define PyAST_FRAGMENT  3


/*  These are the internal objects and definitions required to implement the
 *  AST type.  Most of the internal names are more reminiscent of the 'old'
 *  naming style, but the code uses the new naming convention.
 */

static PyObject*
parser_error = 0;


typedef struct _PyAST_Object {
    PyObject_HEAD                       /* standard object header           */
    node* ast_node;                     /* the node* returned by the parser */
    int   ast_type;                     /* EXPR or SUITE ?                  */
} PyAST_Object;


staticforward void
parser_free(PyAST_Object *ast);

staticforward int
parser_compare(PyAST_Object *left, PyAST_Object *right);

staticforward PyObject *
parser_getattr(PyObject *self, char *name);


static
PyTypeObject PyAST_Type = {
    PyObject_HEAD_INIT(NULL)
    0,
    "ast",                              /* tp_name              */
    (int) sizeof(PyAST_Object),         /* tp_basicsize         */
    0,                                  /* tp_itemsize          */
    (destructor)parser_free,            /* tp_dealloc           */
    0,                                  /* tp_print             */
    parser_getattr,                     /* tp_getattr           */
    0,                                  /* tp_setattr           */
    (cmpfunc)parser_compare,            /* tp_compare           */
    0,                                  /* tp_repr              */
    0,                                  /* tp_as_number         */
    0,                                  /* tp_as_sequence       */
    0,                                  /* tp_as_mapping        */
    0,                                  /* tp_hash              */
    0,                                  /* tp_call              */
    0,                                  /* tp_str               */
    0,                                  /* tp_getattro          */
    0,                                  /* tp_setattro          */

    /* Functions to access object as input/output buffer */
    0,                                  /* tp_as_buffer         */

    Py_TPFLAGS_DEFAULT,                 /* tp_flags             */

    /* __doc__ */
    "Intermediate representation of a Python parse tree."
};  /* PyAST_Type */


static int
parser_compare_nodes(node *left, node *right)
{
    int j;

    if (TYPE(left) < TYPE(right))
        return (-1);

    if (TYPE(right) < TYPE(left))
        return (1);

    if (ISTERMINAL(TYPE(left)))
        return (strcmp(STR(left), STR(right)));

    if (NCH(left) < NCH(right))
        return (-1);

    if (NCH(right) < NCH(left))
        return (1);

    for (j = 0; j < NCH(left); ++j) {
        int v = parser_compare_nodes(CHILD(left, j), CHILD(right, j));

        if (v != 0)
            return (v);
    }
    return (0);
}


/*  int parser_compare(PyAST_Object* left, PyAST_Object* right)
 *
 *  Comparison function used by the Python operators ==, !=, <, >, <=, >=
 *  This really just wraps a call to parser_compare_nodes() with some easy
 *  checks and protection code.
 *
 */
static int
parser_compare(PyAST_Object *left, PyAST_Object *right)
{
    if (left == right)
        return (0);

    if ((left == 0) || (right == 0))
        return (-1);

    return (parser_compare_nodes(left->ast_node, right->ast_node));
}


/*  parser_newastobject(node* ast)
 *
 *  Allocates a new Python object representing an AST.  This is simply the
 *  'wrapper' object that holds a node* and allows it to be passed around in
 *  Python code.
 *
 */
static PyObject*
parser_newastobject(node *ast, int type)
{
    PyAST_Object* o = PyObject_New(PyAST_Object, &PyAST_Type);

    if (o != 0) {
        o->ast_node = ast;
        o->ast_type = type;
    }
    else {
        PyNode_Free(ast);
    }
    return ((PyObject*)o);
}


/*  void parser_free(PyAST_Object* ast)
 *
 *  This is called by a del statement that reduces the reference count to 0.
 *
 */
static void
parser_free(PyAST_Object *ast)
{
    PyNode_Free(ast->ast_node);
    PyObject_Del(ast);
}


/*  parser_ast2tuple(PyObject* self, PyObject* args, PyObject* kw)
 *
 *  This provides conversion from a node* to a tuple object that can be
 *  returned to the Python-level caller.  The AST object is not modified.
 *
 */
static PyObject*
parser_ast2tuple(PyAST_Object *self, PyObject *args, PyObject *kw)
{
    PyObject *line_option = 0;
    PyObject *res = 0;
    int ok;

    static char *keywords[] = {"ast", "line_info", NULL};

    if (self == NULL) {
        ok = PyArg_ParseTupleAndKeywords(args, kw, "O!|O:ast2tuple", keywords,
                                         &PyAST_Type, &self, &line_option);
    }
    else
        ok = PyArg_ParseTupleAndKeywords(args, kw, "|O:totuple", &keywords[1],
                                         &line_option);
    if (ok != 0) {
        int lineno = 0;
        if (line_option != NULL) {
            lineno = (PyObject_IsTrue(line_option) != 0) ? 1 : 0;
        }
        /*
         *  Convert AST into a tuple representation.  Use Guido's function,
         *  since it's known to work already.
         */
        res = node2tuple(((PyAST_Object*)self)->ast_node,
                         PyTuple_New, PyTuple_SetItem, lineno);
    }
    return (res);
}


/*  parser_ast2list(PyObject* self, PyObject* args, PyObject* kw)
 *
 *  This provides conversion from a node* to a list object that can be
 *  returned to the Python-level caller.  The AST object is not modified.
 *
 */
static PyObject*
parser_ast2list(PyAST_Object *self, PyObject *args, PyObject *kw)
{
    PyObject *line_option = 0;
    PyObject *res = 0;
    int ok;

    static char *keywords[] = {"ast", "line_info", NULL};

    if (self == NULL)
        ok = PyArg_ParseTupleAndKeywords(args, kw, "O!|O:ast2list", keywords,
                                         &PyAST_Type, &self, &line_option);
    else
        ok = PyArg_ParseTupleAndKeywords(args, kw, "|O:tolist", &keywords[1],
                                         &line_option);
    if (ok) {
        int lineno = 0;
        if (line_option != 0) {
            lineno = PyObject_IsTrue(line_option) ? 1 : 0;
        }
        /*
         *  Convert AST into a tuple representation.  Use Guido's function,
         *  since it's known to work already.
         */
        res = node2tuple(self->ast_node,
                         PyList_New, PyList_SetItem, lineno);
    }
    return (res);
}


/*  parser_compileast(PyObject* self, PyObject* args)
 *
 *  This function creates code objects from the parse tree represented by
 *  the passed-in data object.  An optional file name is passed in as well.
 *
 */
static PyObject*
parser_compileast(PyAST_Object *self, PyObject *args, PyObject *kw)
{
    PyObject*     res = 0;
    char*         str = "<ast>";
    int ok;

    static char *keywords[] = {"ast", "filename", NULL};

    if (self == NULL)
        ok = PyArg_ParseTupleAndKeywords(args, kw, "O!|s:compileast", keywords,
                                         &PyAST_Type, &self, &str);
    else
        ok = PyArg_ParseTupleAndKeywords(args, kw, "|s:compile", &keywords[1],
                                         &str);

    if (ok)
        res = (PyObject *)PyNode_Compile(self->ast_node, str);

    return (res);
}


/*  PyObject* parser_isexpr(PyObject* self, PyObject* args)
 *  PyObject* parser_issuite(PyObject* self, PyObject* args)
 *
 *  Checks the passed-in AST object to determine if it is an expression or
 *  a statement suite, respectively.  The return is a Python truth value.
 *
 */
static PyObject*
parser_isexpr(PyAST_Object *self, PyObject *args, PyObject *kw)
{
    PyObject* res = 0;
    int ok;

    static char *keywords[] = {"ast", NULL};

    if (self == NULL)
        ok = PyArg_ParseTupleAndKeywords(args, kw, "O!:isexpr", keywords,
                                         &PyAST_Type, &self);
    else
        ok = PyArg_ParseTupleAndKeywords(args, kw, ":isexpr", &keywords[1]);

    if (ok) {
        /* Check to see if the AST represents an expression or not. */
        res = (self->ast_type == PyAST_EXPR) ? Py_True : Py_False;
        Py_INCREF(res);
    }
    return (res);
}


static PyObject*
parser_issuite(PyAST_Object *self, PyObject *args, PyObject *kw)
{
    PyObject* res = 0;
    int ok;

    static char *keywords[] = {"ast", NULL};

    if (self == NULL)
        ok = PyArg_ParseTupleAndKeywords(args, kw, "O!:issuite", keywords,
                                         &PyAST_Type, &self);
    else
        ok = PyArg_ParseTupleAndKeywords(args, kw, ":issuite", &keywords[1]);

    if (ok) {
        /* Check to see if the AST represents an expression or not. */
        res = (self->ast_type == PyAST_EXPR) ? Py_False : Py_True;
        Py_INCREF(res);
    }
    return (res);
}


#define PUBLIC_METHOD_TYPE (METH_VARARGS|METH_KEYWORDS)

static PyMethodDef
parser_methods[] = {
    {"compile",         (PyCFunction)parser_compileast, PUBLIC_METHOD_TYPE,
        "Compile this AST object into a code object."},
    {"isexpr",          (PyCFunction)parser_isexpr,     PUBLIC_METHOD_TYPE,
        "Determines if this AST object was created from an expression."},
    {"issuite",         (PyCFunction)parser_issuite,    PUBLIC_METHOD_TYPE,
        "Determines if this AST object was created from a suite."},
    {"tolist",          (PyCFunction)parser_ast2list,   PUBLIC_METHOD_TYPE,
        "Creates a list-tree representation of this AST."},
    {"totuple",         (PyCFunction)parser_ast2tuple,  PUBLIC_METHOD_TYPE,
        "Creates a tuple-tree representation of this AST."},

    {NULL, NULL, 0, NULL}
};


static PyObject*
parser_getattr(self, name)
     PyObject *self;
     char *name;
{
    return (Py_FindMethod(parser_methods, self, name));
}


/*  err_string(char* message)
 *
 *  Sets the error string for an exception of type ParserError.
 *
 */
static void
err_string(message)
     char *message;
{
    PyErr_SetString(parser_error, message);
}


/*  PyObject* parser_do_parse(PyObject* args, int type)
 *
 *  Internal function to actually execute the parse and return the result if
 *  successful, or set an exception if not.
 *
 */
static PyObject*
parser_do_parse(PyObject *args, PyObject *kw, char *argspec, int type)
{
    char*     string = 0;
    PyObject* res    = 0;

    static char *keywords[] = {"source", NULL};

    if (PyArg_ParseTupleAndKeywords(args, kw, argspec, keywords, &string)) {
        node* n = PyParser_SimpleParseString(string,
                                             (type == PyAST_EXPR)
                                             ? eval_input : file_input);

        if (n != 0)
            res = parser_newastobject(n, type);
        else
            err_string("Could not parse string.");
    }
    return (res);
}


/*  PyObject* parser_expr(PyObject* self, PyObject* args)
 *  PyObject* parser_suite(PyObject* self, PyObject* args)
 *
 *  External interfaces to the parser itself.  Which is called determines if
 *  the parser attempts to recognize an expression ('eval' form) or statement
 *  suite ('exec' form).  The real work is done by parser_do_parse() above.
 *
 */
static PyObject*
parser_expr(PyAST_Object *self, PyObject *args, PyObject *kw)
{
    NOTE(ARGUNUSED(self))
    return (parser_do_parse(args, kw, "s:expr", PyAST_EXPR));
}


static PyObject*
parser_suite(PyAST_Object *self, PyObject *args, PyObject *kw)
{
    NOTE(ARGUNUSED(self))
    return (parser_do_parse(args, kw, "s:suite", PyAST_SUITE));
}



/*  This is the messy part of the code.  Conversion from a tuple to an AST
 *  object requires that the input tuple be valid without having to rely on
 *  catching an exception from the compiler.  This is done to allow the
 *  compiler itself to remain fast, since most of its input will come from
 *  the parser directly, and therefore be known to be syntactically correct.
 *  This validation is done to ensure that we don't core dump the compile
 *  phase, returning an exception instead.
 *
 *  Two aspects can be broken out in this code:  creating a node tree from
 *  the tuple passed in, and verifying that it is indeed valid.  It may be
 *  advantageous to expand the number of AST types to include funcdefs and
 *  lambdadefs to take advantage of the optimizer, recognizing those ASTs
 *  here.  They are not necessary, and not quite as useful in a raw form.
 *  For now, let's get expressions and suites working reliably.
 */


staticforward node* build_node_tree(PyObject *tuple);
staticforward int   validate_expr_tree(node *tree);
staticforward int   validate_file_input(node *tree);


/*  PyObject* parser_tuple2ast(PyObject* self, PyObject* args)
 *
 *  This is the public function, called from the Python code.  It receives a
 *  single tuple object from the caller, and creates an AST object if the
 *  tuple can be validated.  It does this by checking the first code of the
 *  tuple, and, if acceptable, builds the internal representation.  If this
 *  step succeeds, the internal representation is validated as fully as
 *  possible with the various validate_*() routines defined below.
 *
 *  This function must be changed if support is to be added for PyAST_FRAGMENT
 *  AST objects.
 *
 */
static PyObject*
parser_tuple2ast(PyAST_Object *self, PyObject *args, PyObject *kw)
{
    NOTE(ARGUNUSED(self))
    PyObject *ast = 0;
    PyObject *tuple = 0;
    PyObject *temp = 0;
    int ok;
    int start_sym = 0;

    static char *keywords[] = {"sequence", NULL};

    if (!PyArg_ParseTupleAndKeywords(args, kw, "O:tuple2ast", keywords,
                                     &tuple))
        return (0);
    if (!PySequence_Check(tuple)) {
        PyErr_SetString(PyExc_ValueError,
                        "tuple2ast() requires a single sequence argument");
        return (0);
    }
    /*
     *  This mess of tests is written this way so we can use the abstract
     *  object interface (AOI).  Unfortunately, the AOI increments reference
     *  counts, which requires that we store a pointer to retrieved object
     *  so we can DECREF it after the check.  But we really should accept
     *  lists as well as tuples at the very least.
     */
    ok = PyObject_Length(tuple) >= 2;
    if (ok) {
        temp = PySequence_GetItem(tuple, 0);
        ok = (temp != NULL) && PyInt_Check(temp);
        if (ok)
            /* this is used after the initial checks: */
            start_sym = PyInt_AS_LONG(temp);
        Py_XDECREF(temp);
    }
    if (ok) {
        temp = PySequence_GetItem(tuple, 1);
        ok = (temp != NULL) && PySequence_Check(temp);
        Py_XDECREF(temp);
    }
    if (ok) {
        temp = PySequence_GetItem(tuple, 1);
        ok = (temp != NULL) && PyObject_Length(temp) >= 2;
        if (ok) {
            PyObject *temp2 = PySequence_GetItem(temp, 0);
            if (temp2 != NULL) {
                ok = PyInt_Check(temp2);
                Py_DECREF(temp2);
            }
        }
        Py_XDECREF(temp);
    }
    /* If we've failed at some point, get out of here. */
    if (!ok) {
        err_string("malformed sequence for tuple2ast()");
        return (0);
    }
    /*
     *  This might be a valid parse tree, but let's do a quick check
     *  before we jump the gun.
     */
    if (start_sym == eval_input) {
        /*  Might be an eval form.  */
        node* expression = build_node_tree(tuple);

        if ((expression != 0) && validate_expr_tree(expression))
            ast = parser_newastobject(expression, PyAST_EXPR);
    }
    else if (start_sym == file_input) {
        /*  This looks like an exec form so far.  */
        node* suite_tree = build_node_tree(tuple);

        if ((suite_tree != 0) && validate_file_input(suite_tree))
            ast = parser_newastobject(suite_tree, PyAST_SUITE);
    }
    else
        /*  This is a fragment, and is not yet supported.  Maybe they
         *  will be if I find a use for them.
         */
        err_string("Fragmentary parse trees not supported.");

    /*  Make sure we throw an exception on all errors.  We should never
     *  get this, but we'd do well to be sure something is done.
     */
    if ((ast == 0) && !PyErr_Occurred())
        err_string("Unspecified ast error occurred.");

    return (ast);
}


/*  int check_terminal_tuple()
 *
 *  Check a tuple to determine that it is indeed a valid terminal
 *  node.  The node is known to be required as a terminal, so we throw
 *  an exception if there is a failure.
 *
 *  The format of an acceptable terminal tuple is "(is[i])": the fact
 *  that elem is a tuple and the integer is a valid terminal symbol
 *  has been established before this function is called.  We must
 *  check the length of the tuple and the type of the second element
 *  and optional third element.  We do *NOT* check the actual text of
 *  the string element, which we could do in many cases.  This is done
 *  by the validate_*() functions which operate on the internal
 *  representation.
 */
static int
check_terminal_tuple(PyObject *elem)
{
    int   len = PyObject_Length(elem);
    int   res = 1;
    char* str = "Illegal terminal symbol; bad node length.";

    if ((len == 2) || (len == 3)) {
        PyObject *temp = PySequence_GetItem(elem, 1);
        res = PyString_Check(temp);
        str = "Illegal terminal symbol; expected a string.";
        if (res && (len == 3)) {
            PyObject* third = PySequence_GetItem(elem, 2);
            res = PyInt_Check(third);
            str = "Invalid third element of terminal node.";
            Py_XDECREF(third);
        }
        Py_XDECREF(temp);
    }
    else {
        res = 0;
    }
    if (!res) {
        elem = Py_BuildValue("(os)", elem, str);
        PyErr_SetObject(parser_error, elem);
    }
    return (res);
}


/*  node* build_node_children()
 *
 *  Iterate across the children of the current non-terminal node and build
 *  their structures.  If successful, return the root of this portion of
 *  the tree, otherwise, 0.  Any required exception will be specified already,
 *  and no memory will have been deallocated.
 *
 */
static node*
build_node_children(PyObject *tuple, node *root, int *line_num)
{
    int len = PyObject_Length(tuple);
    int i;

    for (i = 1; i < len; ++i) {
        /* elem must always be a tuple, however simple */
        PyObject* elem = PySequence_GetItem(tuple, i);
        int ok = elem != NULL;
        long  type = 0;
        char *strn = 0;

        if (ok)
            ok = PySequence_Check(elem);
        if (ok) {
            PyObject *temp = PySequence_GetItem(elem, 0);
            if (temp == NULL)
                ok = 0;
            else {
                ok = PyInt_Check(temp);
                if (ok)
                    type = PyInt_AS_LONG(temp);
                Py_DECREF(temp);
            }
        }
        if (!ok) {
            PyErr_SetObject(parser_error,
                            Py_BuildValue("(os)", elem,
                                          "Illegal node construct."));
            Py_XDECREF(elem);
            return (0);
        }
        if (ISTERMINAL(type)) {
            if (check_terminal_tuple(elem)) {
                PyObject *temp = PySequence_GetItem(elem, 1);

                /* check_terminal_tuple() already verified it's a string */
                strn = (char *)PyMem_MALLOC(PyString_GET_SIZE(temp) + 1);
                if (strn != NULL)
                    (void) strcpy(strn, PyString_AS_STRING(temp));
                Py_DECREF(temp);

                if (PyObject_Length(elem) == 3) {
                    PyObject* temp = PySequence_GetItem(elem, 2);
                    *line_num = PyInt_AsLong(temp);
                    Py_DECREF(temp);
                }
            }
            else {
                Py_XDECREF(elem);
                return (0);
            }
        }
        else if (!ISNONTERMINAL(type)) {
            /*
             *  It has to be one or the other; this is an error.
             *  Throw an exception.
             */
            PyErr_SetObject(parser_error,
                            Py_BuildValue("(os)", elem,
                                          "Unknown node type."));
            Py_XDECREF(elem);
            return (0);
        }
        PyNode_AddChild(root, type, strn, *line_num);

        if (ISNONTERMINAL(type)) {
            node* new_child = CHILD(root, i - 1);

            if (new_child != build_node_children(elem, new_child, line_num)) {
                Py_XDECREF(elem);
                return (0);
            }
        }
        else if (type == NEWLINE) {     /* It's true:  we increment the     */
            ++(*line_num);              /* line number *after* the newline! */
        }
        Py_XDECREF(elem);
    }
    return (root);
}


static node*
build_node_tree(PyObject *tuple)
{
    node* res = 0;
    PyObject *temp = PySequence_GetItem(tuple, 0);
    long  num = -1;

    if (temp != NULL)
        num = PyInt_AsLong(temp);
    Py_XDECREF(temp);
    if (ISTERMINAL(num)) {
        /*
         *  The tuple is simple, but it doesn't start with a start symbol.
         *  Throw an exception now and be done with it.
         */
        tuple = Py_BuildValue("(os)", tuple,
                    "Illegal ast tuple; cannot start with terminal symbol.");
        PyErr_SetObject(parser_error, tuple);
    }
    else if (ISNONTERMINAL(num)) {
        /*
         *  Not efficient, but that can be handled later.
         */
        int line_num = 0;

        res = PyNode_New(num);
        if (res != build_node_children(tuple, res, &line_num)) {
            PyNode_Free(res);
            res = 0;
        }
    }
    else
        /*  The tuple is illegal -- if the number is neither TERMINAL nor
         *  NONTERMINAL, we can't use it.
         */
        PyErr_SetObject(parser_error,
                        Py_BuildValue("(os)", tuple,
                                      "Illegal component tuple."));

    return (res);
}


#ifdef HAVE_OLD_CPP
#define VALIDATER(n)    static int validate_/**/n(node *tree)
#else
#define VALIDATER(n)    static int validate_##n(node *tree)
#endif


/*
 *  Validation routines used within the validation section:
 */
staticforward int validate_terminal(node *terminal, int type, char *string);

#define validate_ampersand(ch)  validate_terminal(ch,      AMPER, "&")
#define validate_circumflex(ch) validate_terminal(ch, CIRCUMFLEX, "^")
#define validate_colon(ch)      validate_terminal(ch,      COLON, ":")
#define validate_comma(ch)      validate_terminal(ch,      COMMA, ",")
#define validate_dedent(ch)     validate_terminal(ch,     DEDENT, "")
#define validate_equal(ch)      validate_terminal(ch,      EQUAL, "=")
#define validate_indent(ch)     validate_terminal(ch,     INDENT, (char*)NULL)
#define validate_lparen(ch)     validate_terminal(ch,       LPAR, "(")
#define validate_newline(ch)    validate_terminal(ch,    NEWLINE, (char*)NULL)
#define validate_rparen(ch)     validate_terminal(ch,       RPAR, ")")
#define validate_semi(ch)       validate_terminal(ch,       SEMI, ";")
#define validate_star(ch)       validate_terminal(ch,       STAR, "*")
#define validate_vbar(ch)       validate_terminal(ch,       VBAR, "|")
#define validate_doublestar(ch) validate_terminal(ch, DOUBLESTAR, "**")
#define validate_dot(ch)        validate_terminal(ch,        DOT, ".")
#define validate_name(ch, str)  validate_terminal(ch,       NAME, str)

VALIDATER(node);                VALIDATER(small_stmt);
VALIDATER(class);               VALIDATER(node);
VALIDATER(parameters);          VALIDATER(suite);
VALIDATER(testlist);            VALIDATER(varargslist);
VALIDATER(fpdef);               VALIDATER(fplist);
VALIDATER(stmt);                VALIDATER(simple_stmt);
VALIDATER(expr_stmt);           VALIDATER(power);
VALIDATER(print_stmt);          VALIDATER(del_stmt);
VALIDATER(return_stmt);
VALIDATER(raise_stmt);          VALIDATER(import_stmt);
VALIDATER(global_stmt);
VALIDATER(assert_stmt);
VALIDATER(exec_stmt);           VALIDATER(compound_stmt);
VALIDATER(while);               VALIDATER(for);
VALIDATER(try);                 VALIDATER(except_clause);
VALIDATER(test);                VALIDATER(and_test);
VALIDATER(not_test);            VALIDATER(comparison);
VALIDATER(comp_op);             VALIDATER(expr);
VALIDATER(xor_expr);            VALIDATER(and_expr);
VALIDATER(shift_expr);          VALIDATER(arith_expr);
VALIDATER(term);                VALIDATER(factor);
VALIDATER(atom);                VALIDATER(lambdef);
VALIDATER(trailer);             VALIDATER(subscript);
VALIDATER(subscriptlist);       VALIDATER(sliceop);
VALIDATER(exprlist);            VALIDATER(dictmaker);
VALIDATER(arglist);             VALIDATER(argument);


#define is_even(n)      (((n) & 1) == 0)
#define is_odd(n)       (((n) & 1) == 1)


static int
validate_ntype(node *n, int t)
{
    int res = (TYPE(n) == t);

    if (!res) {
        char buffer[128];
        (void) sprintf(buffer, "Expected node type %d, got %d.", t, TYPE(n));
        err_string(buffer);
    }
    return (res);
}


/*  Verifies that the number of child nodes is exactly 'num', raising
 *  an exception if it isn't.  The exception message does not indicate
 *  the exact number of nodes, allowing this to be used to raise the
 *  "right" exception when the wrong number of nodes is present in a
 *  specific variant of a statement's syntax.  This is commonly used
 *  in that fashion.
 */
static int
validate_numnodes(node *n, int num, const char *const name)
{
    if (NCH(n) != num) {
        char buff[60];
        (void) sprintf(buff, "Illegal number of children for %s node.", name);
        err_string(buff);
    }
    return (NCH(n) == num);
}


static int
validate_terminal(node *terminal, int type, char *string)
{
    int res = (validate_ntype(terminal, type)
               && ((string == 0) || (strcmp(string, STR(terminal)) == 0)));

    if (!res && !PyErr_Occurred()) {
        char buffer[60];
        (void) sprintf(buffer, "Illegal terminal: expected \"%s\"", string);
        err_string(buffer);
    }
    return (res);
}


/*  X (',' X) [',']
 */
static int
validate_repeating_list(node *tree, int ntype, int (*vfunc)(),
                        const char *const name)
{
    int nch = NCH(tree);
    int res = (nch && validate_ntype(tree, ntype)
               && vfunc(CHILD(tree, 0)));

    if (!res && !PyErr_Occurred())
        (void) validate_numnodes(tree, 1, name);
    else {
        if (is_even(nch))
            res = validate_comma(CHILD(tree, --nch));
        if (res && nch > 1) {
            int pos = 1;
            for ( ; res && pos < nch; pos += 2)
                res = (validate_comma(CHILD(tree, pos))
                       && vfunc(CHILD(tree, pos + 1)));
        }
    }
    return (res);
}


/*  VALIDATE(class)
 *
 *  classdef:
 *      'class' NAME ['(' testlist ')'] ':' suite
 */
static int
validate_class(node *tree)
{
    int nch = NCH(tree);
    int res = validate_ntype(tree, classdef) && ((nch == 4) || (nch == 7));

    if (res) {
        res = (validate_name(CHILD(tree, 0), "class")
               && validate_ntype(CHILD(tree, 1), NAME)
               && validate_colon(CHILD(tree, nch - 2))
               && validate_suite(CHILD(tree, nch - 1)));
    }
    else
        (void) validate_numnodes(tree, 4, "class");
    if (res && (nch == 7)) {
        res = (validate_lparen(CHILD(tree, 2))
               && validate_testlist(CHILD(tree, 3))
               && validate_rparen(CHILD(tree, 4)));
    }
    return (res);
}


/*  if_stmt:
 *      'if' test ':' suite ('elif' test ':' suite)* ['else' ':' suite]
 */
static int
validate_if(node *tree)
{
    int nch = NCH(tree);
    int res = (validate_ntype(tree, if_stmt)
               && (nch >= 4)
               && validate_name(CHILD(tree, 0), "if")
               && validate_test(CHILD(tree, 1))
               && validate_colon(CHILD(tree, 2))
               && validate_suite(CHILD(tree, 3)));

    if (res && ((nch % 4) == 3)) {
        /*  ... 'else' ':' suite  */
        res = (validate_name(CHILD(tree, nch - 3), "else")
               && validate_colon(CHILD(tree, nch - 2))
               && validate_suite(CHILD(tree, nch - 1)));
        nch -= 3;
    }
    else if (!res && !PyErr_Occurred())
        (void) validate_numnodes(tree, 4, "if");
    if ((nch % 4) != 0)
        /* Will catch the case for nch < 4 */
        res = validate_numnodes(tree, 0, "if");
    else if (res && (nch > 4)) {
        /*  ... ('elif' test ':' suite)+ ...  */
        int j = 4;
        while ((j < nch) && res) {
            res = (validate_name(CHILD(tree, j), "elif")
                   && validate_colon(CHILD(tree, j + 2))
                   && validate_test(CHILD(tree, j + 1))
                   && validate_suite(CHILD(tree, j + 3)));
            j += 4;
        }
    }
    return (res);
}


/*  parameters:
 *      '(' [varargslist] ')'
 *
 */
static int
validate_parameters(node *tree)
{
    int nch = NCH(tree);
    int res = validate_ntype(tree, parameters) && ((nch == 2) || (nch == 3));

    if (res) {
        res = (validate_lparen(CHILD(tree, 0))
               && validate_rparen(CHILD(tree, nch - 1)));
        if (res && (nch == 3))
            res = validate_varargslist(CHILD(tree, 1));
    }
    else {
        (void) validate_numnodes(tree, 2, "parameters");
    }
    return (res);
}


/*  VALIDATE(suite)
 *
 *  suite:
 *      simple_stmt
 *    | NEWLINE INDENT stmt+ DEDENT
 */
static int
validate_suite(node *tree)
{
    int nch = NCH(tree);
    int res = (validate_ntype(tree, suite) && ((nch == 1) || (nch >= 4)));

    if (res && (nch == 1))
        res = validate_simple_stmt(CHILD(tree, 0));
    else if (res) {
        /*  NEWLINE INDENT stmt+ DEDENT  */
        res = (validate_newline(CHILD(tree, 0))
               && validate_indent(CHILD(tree, 1))
               && validate_stmt(CHILD(tree, 2))
               && validate_dedent(CHILD(tree, nch - 1)));

        if (res && (nch > 4)) {
            int i = 3;
            --nch;                      /* forget the DEDENT     */
            for ( ; res && (i < nch); ++i)
                res = validate_stmt(CHILD(tree, i));
        }
        else if (nch < 4)
            res = validate_numnodes(tree, 4, "suite");
    }
    return (res);
}


static int
validate_testlist(node *tree)
{
    return (validate_repeating_list(tree, testlist,
                                    validate_test, "testlist"));
}


/*  VALIDATE(varargslist)
 *
 *  varargslist:
 *      (fpdef ['=' test] ',')* ('*' NAME [',' '*' '*' NAME] | '*' '*' NAME)
 *    | fpdef ['=' test] (',' fpdef ['=' test])* [',']
 *
 *      (fpdef ['=' test] ',')*
 *           ('*' NAME [',' ('**'|'*' '*') NAME]
 *         | ('**'|'*' '*') NAME)
 *    | fpdef ['=' test] (',' fpdef ['=' test])* [',']
 *
 */
static int
validate_varargslist(node *tree)
{
    int nch = NCH(tree);
    int res = validate_ntype(tree, varargslist) && (nch != 0);

    if (res && (nch >= 2) && (TYPE(CHILD(tree, nch - 1)) == NAME)) {
        /*  (fpdef ['=' test] ',')*
         *  ('*' NAME [',' '*' '*' NAME] | '*' '*' NAME)
         */
        int pos = 0;
        int remaining = nch;

        while (res && (TYPE(CHILD(tree, pos)) == fpdef)) {
            res = validate_fpdef(CHILD(tree, pos));
            if (res) {
                if (TYPE(CHILD(tree, pos + 1)) == EQUAL) {
                    res = validate_test(CHILD(tree, pos + 2));
                    pos += 2;
                }
                res = res && validate_comma(CHILD(tree, pos + 1));
                pos += 2;
            }
        }
        if (res) {
            remaining = nch - pos;
            res = ((remaining == 2) || (remaining == 3)
                   || (remaining == 5) || (remaining == 6));
            if (!res)
                (void) validate_numnodes(tree, 2, "varargslist");
            else if (TYPE(CHILD(tree, pos)) == DOUBLESTAR)
                return ((remaining == 2)
                        && validate_ntype(CHILD(tree, pos+1), NAME));
            else {
                res = validate_star(CHILD(tree, pos++));
                --remaining;
            }
        }
        if (res) {
            if (remaining == 2) {
                res = (validate_star(CHILD(tree, pos))
                       && validate_ntype(CHILD(tree, pos + 1), NAME));
            }
            else {
                res = validate_ntype(CHILD(tree, pos++), NAME);
                if (res && (remaining >= 4)) {
                    res = validate_comma(CHILD(tree, pos));
                    if (--remaining == 3)
                        res = (validate_star(CHILD(tree, pos + 1))
                               && validate_star(CHILD(tree, pos + 2)));
                    else
                        res = validate_ntype(CHILD(tree, pos + 1), DOUBLESTAR);
                }
            }
        }
        if (!res && !PyErr_Occurred())
            err_string("Incorrect validation of variable arguments list.");
    }
    else if (res) {
        /*  fpdef ['=' test] (',' fpdef ['=' test])* [',']  */
        if (TYPE(CHILD(tree, nch - 1)) == COMMA)
            --nch;

        /*  fpdef ['=' test] (',' fpdef ['=' test])*  */
        res = (is_odd(nch)
               && validate_fpdef(CHILD(tree, 0)));

        if (res && (nch > 1)) {
            int pos = 1;
            if (TYPE(CHILD(tree, 1)) == EQUAL) {
                res = validate_test(CHILD(tree, 2));
                pos += 2;
            }
            /*  ... (',' fpdef ['=' test])*  */
            for ( ; res && (pos < nch); pos += 2) {
                /* ',' fpdef */
                res = (validate_comma(CHILD(tree, pos))
                       && validate_fpdef(CHILD(tree, pos + 1)));
                if (res
                    && ((nch - pos) > 2)
                    && (TYPE(CHILD(tree, pos + 2)) == EQUAL)) {
                    /* ['=' test] */
                    res = validate_test(CHILD(tree, pos + 3));
                    pos += 2;
                }
            }
        }
    }
    else {
        err_string("Improperly formed argument list.");
    }
    return (res);
}


/*  VALIDATE(fpdef)
 *
 *  fpdef:
 *      NAME
 *    | '(' fplist ')'
 */
static int
validate_fpdef(node *tree)
{
    int nch = NCH(tree);
    int res = validate_ntype(tree, fpdef);

    if (res) {
        if (nch == 1)
            res = validate_ntype(CHILD(tree, 0), NAME);
        else if (nch == 3)
            res = (validate_lparen(CHILD(tree, 0))
                   && validate_fplist(CHILD(tree, 1))
                   && validate_rparen(CHILD(tree, 2)));
        else
            res = validate_numnodes(tree, 1, "fpdef");
    }
    return (res);
}


static int
validate_fplist(node *tree)
{
    return (validate_repeating_list(tree, fplist,
                                    validate_fpdef, "fplist"));
}


/*  simple_stmt | compound_stmt
 *
 */
static int
validate_stmt(node *tree)
{
    int res = (validate_ntype(tree, stmt)
               && validate_numnodes(tree, 1, "stmt"));

    if (res) {
        tree = CHILD(tree, 0);

        if (TYPE(tree) == simple_stmt)
            res = validate_simple_stmt(tree);
        else
            res = validate_compound_stmt(tree);
    }
    return (res);
}


/*  small_stmt (';' small_stmt)* [';'] NEWLINE
 *
 */
static int
validate_simple_stmt(node *tree)
{
    int nch = NCH(tree);
    int res = (validate_ntype(tree, simple_stmt)
               && (nch >= 2)
               && validate_small_stmt(CHILD(tree, 0))
               && validate_newline(CHILD(tree, nch - 1)));

    if (nch < 2)
        res = validate_numnodes(tree, 2, "simple_stmt");
    --nch;                              /* forget the NEWLINE    */
    if (res && is_even(nch))
        res = validate_semi(CHILD(tree, --nch));
    if (res && (nch > 2)) {
        int i;

        for (i = 1; res && (i < nch); i += 2)
            res = (validate_semi(CHILD(tree, i))
                   && validate_small_stmt(CHILD(tree, i + 1)));
    }
    return (res);
}


static int
validate_small_stmt(node *tree)
{
    int nch = NCH(tree);
    int res = (validate_numnodes(tree, 1, "small_stmt")
               && ((TYPE(CHILD(tree, 0)) == expr_stmt)
                   || (TYPE(CHILD(tree, 0)) == print_stmt)
                   || (TYPE(CHILD(tree, 0)) == del_stmt)
                   || (TYPE(CHILD(tree, 0)) == pass_stmt)
                   || (TYPE(CHILD(tree, 0)) == flow_stmt)
                   || (TYPE(CHILD(tree, 0)) == import_stmt)
                   || (TYPE(CHILD(tree, 0)) == global_stmt)
                   || (TYPE(CHILD(tree, 0)) == assert_stmt)
                   || (TYPE(CHILD(tree, 0)) == exec_stmt)));

    if (res)
        res = validate_node(CHILD(tree, 0));
    else if (nch == 1) {
        char buffer[60];
        (void) sprintf(buffer, "Unrecognized child node of small_stmt: %d.",
                       TYPE(CHILD(tree, 0)));
        err_string(buffer);
    }
    return (res);
}


/*  compound_stmt:
 *      if_stmt | while_stmt | for_stmt | try_stmt | funcdef | classdef
 */
static int
validate_compound_stmt(node *tree)
{
    int res = (validate_ntype(tree, compound_stmt)
               && validate_numnodes(tree, 1, "compound_stmt"));

    if (!res)
        return (0);

    tree = CHILD(tree, 0);
    res = ((TYPE(tree) == if_stmt)
           || (TYPE(tree) == while_stmt)
           || (TYPE(tree) == for_stmt)
           || (TYPE(tree) == try_stmt)
           || (TYPE(tree) == funcdef)
           || (TYPE(tree) == classdef));
    if (res)
        res = validate_node(tree);
    else {
        char buffer[60];
        (void) sprintf(buffer, "Illegal compound statement type: %d.",
                       TYPE(tree));
        err_string(buffer);
    }
    return (res);
}


static int
validate_expr_stmt(node *tree)
{
    int j;
    int nch = NCH(tree);
    int res = (validate_ntype(tree, expr_stmt)
               && is_odd(nch)
               && validate_testlist(CHILD(tree, 0)));

    for (j = 1; res && (j < nch); j += 2)
        res = (validate_equal(CHILD(tree, j))
               && validate_testlist(CHILD(tree, j + 1)));

    return (res);
}


/*  print_stmt:
 *
 *      'print' (test ',')* [test]
 *
 */
static int
validate_print_stmt(node *tree)
{
    int j;
    int nch = NCH(tree);
    int res = (validate_ntype(tree, print_stmt)
               && (nch != 0)
               && validate_name(CHILD(tree, 0), "print"));

    if (res && is_even(nch)) {
        res = validate_test(CHILD(tree, nch - 1));
        --nch;
    }
    else if (!res && !PyErr_Occurred())
        (void) validate_numnodes(tree, 1, "print_stmt");
    for (j = 1; res && (j < nch); j += 2)
        res = (validate_test(CHILD(tree, j))
               && validate_ntype(CHILD(tree, j + 1), COMMA));

    return (res);
}


static int
validate_del_stmt(node *tree)
{
    return (validate_numnodes(tree, 2, "del_stmt")
            && validate_name(CHILD(tree, 0), "del")
            && validate_exprlist(CHILD(tree, 1)));
}


static int
validate_return_stmt(node *tree)
{
    int nch = NCH(tree);
    int res = (validate_ntype(tree, return_stmt)
               && ((nch == 1) || (nch == 2))
               && validate_name(CHILD(tree, 0), "return"));

    if (res && (nch == 2))
        res = validate_testlist(CHILD(tree, 1));

    return (res);
}


static int
validate_raise_stmt(node *tree)
{
    int nch = NCH(tree);
    int res = (validate_ntype(tree, raise_stmt)
               && ((nch == 1) || (nch == 2) || (nch == 4) || (nch == 6)));

    if (res) {
        res = validate_name(CHILD(tree, 0), "raise");
        if (res && (nch >= 2))
            res = validate_test(CHILD(tree, 1));
        if (res && nch > 2) {
            res = (validate_comma(CHILD(tree, 2))
                   && validate_test(CHILD(tree, 3)));
            if (res && (nch > 4))
                res = (validate_comma(CHILD(tree, 4))
                       && validate_test(CHILD(tree, 5)));
        }
    }
    else
        (void) validate_numnodes(tree, 2, "raise");
    if (res && (nch == 4))
        res = (validate_comma(CHILD(tree, 2))
               && validate_test(CHILD(tree, 3)));

    return (res);
}


/*  import_stmt:
 *
 *    'import' dotted_name (',' dotted_name)*
 *  | 'from' dotted_name 'import' ('*' | NAME (',' NAME)*)
 */
static int
validate_import_stmt(node *tree)
{
    int nch = NCH(tree);
    int res = (validate_ntype(tree, import_stmt)
               && (nch >= 2) && is_even(nch)
               && validate_ntype(CHILD(tree, 0), NAME)
               && validate_ntype(CHILD(tree, 1), dotted_name));

    if (res && (strcmp(STR(CHILD(tree, 0)), "import") == 0)) {
        int j;

        for (j = 2; res && (j < nch); j += 2)
            res = (validate_comma(CHILD(tree, j))
                   && validate_ntype(CHILD(tree, j + 1), dotted_name));
    }
    else if (res && validate_name(CHILD(tree, 0), "from")) {
        res = ((nch >= 4) && is_even(nch)
               && validate_name(CHILD(tree, 2), "import"));
        if (nch == 4) {
            res = ((TYPE(CHILD(tree, 3)) == NAME)
                   || (TYPE(CHILD(tree, 3)) == STAR));
            if (!res)
                err_string("Illegal import statement.");
        }
        else {
            /*  'from' NAME 'import' NAME (',' NAME)+  */
            int j;
            res = validate_ntype(CHILD(tree, 3), NAME);
            for (j = 4; res && (j < nch); j += 2)
                res = (validate_comma(CHILD(tree, j))
                       && validate_ntype(CHILD(tree, j + 1), NAME));
        }
    }
    else
        res = 0;

    return (res);
}


static int
validate_global_stmt(node *tree)
{
    int j;
    int nch = NCH(tree);
    int res = (validate_ntype(tree, global_stmt)
               && is_even(nch) && (nch >= 2));

    if (res)
        res = (validate_name(CHILD(tree, 0), "global")
               && validate_ntype(CHILD(tree, 1), NAME));
    for (j = 2; res && (j < nch); j += 2)
        res = (validate_comma(CHILD(tree, j))
               && validate_ntype(CHILD(tree, j + 1), NAME));

    return (res);
}


/*  exec_stmt:
 *
 *  'exec' expr ['in' test [',' test]]
 */
static int
validate_exec_stmt(node *tree)
{
    int nch = NCH(tree);
    int res = (validate_ntype(tree, exec_stmt)
               && ((nch == 2) || (nch == 4) || (nch == 6))
               && validate_name(CHILD(tree, 0), "exec")
               && validate_expr(CHILD(tree, 1)));

    if (!res && !PyErr_Occurred())
        err_string("Illegal exec statement.");
    if (res && (nch > 2))
        res = (validate_name(CHILD(tree, 2), "in")
               && validate_test(CHILD(tree, 3)));
    if (res && (nch == 6))
        res = (validate_comma(CHILD(tree, 4))
               && validate_test(CHILD(tree, 5)));

    return (res);
}


/*  assert_stmt:
 *
 *  'assert' test [',' test]
 */
static int
validate_assert_stmt(node *tree)
{
    int nch = NCH(tree);
    int res = (validate_ntype(tree, assert_stmt)
               && ((nch == 2) || (nch == 4))
               && (validate_name(CHILD(tree, 0), "__assert__") ||
                   validate_name(CHILD(tree, 0), "assert"))
               && validate_test(CHILD(tree, 1)));

    if (!res && !PyErr_Occurred())
        err_string("Illegal assert statement.");
    if (res && (nch > 2))
        res = (validate_comma(CHILD(tree, 2))
               && validate_test(CHILD(tree, 3)));

    return (res);
}


static int
validate_while(node *tree)
{
    int nch = NCH(tree);
    int res = (validate_ntype(tree, while_stmt)
               && ((nch == 4) || (nch == 7))
               && validate_name(CHILD(tree, 0), "while")
               && validate_test(CHILD(tree, 1))
               && validate_colon(CHILD(tree, 2))
               && validate_suite(CHILD(tree, 3)));

    if (res && (nch == 7))
        res = (validate_name(CHILD(tree, 4), "else")
               && validate_colon(CHILD(tree, 5))
               && validate_suite(CHILD(tree, 6)));

    return (res);
}


static int
validate_for(node *tree)
{
    int nch = NCH(tree);
    int res = (validate_ntype(tree, for_stmt)
               && ((nch == 6) || (nch == 9))
               && validate_name(CHILD(tree, 0), "for")
               && validate_exprlist(CHILD(tree, 1))
               && validate_name(CHILD(tree, 2), "in")
               && validate_testlist(CHILD(tree, 3))
               && validate_colon(CHILD(tree, 4))
               && validate_suite(CHILD(tree, 5)));

    if (res && (nch == 9))
        res = (validate_name(CHILD(tree, 6), "else")
               && validate_colon(CHILD(tree, 7))
               && validate_suite(CHILD(tree, 8)));

    return (res);
}


/*  try_stmt:
 *      'try' ':' suite (except_clause ':' suite)+ ['else' ':' suite]
 *    | 'try' ':' suite 'finally' ':' suite
 *
 */
static int
validate_try(tree)
    node *tree;
{
    int nch = NCH(tree);
    int pos = 3;
    int res = (validate_ntype(tree, try_stmt)
               && (nch >= 6) && ((nch % 3) == 0));

    if (res)
        res = (validate_name(CHILD(tree, 0), "try")
               && validate_colon(CHILD(tree, 1))
               && validate_suite(CHILD(tree, 2))
               && validate_colon(CHILD(tree, nch - 2))
               && validate_suite(CHILD(tree, nch - 1)));
    else {
        const char* name = "execpt";
        char buffer[60];
        if (TYPE(CHILD(tree, nch - 3)) != except_clause)
            name = STR(CHILD(tree, nch - 3));
        (void) sprintf(buffer,
                       "Illegal number of children for try/%s node.", name);
        err_string(buffer);
    }
    /*  Skip past except_clause sections:  */
    while (res && (TYPE(CHILD(tree, pos)) == except_clause)) {
        res = (validate_except_clause(CHILD(tree, pos))
               && validate_colon(CHILD(tree, pos + 1))
               && validate_suite(CHILD(tree, pos + 2)));
        pos += 3;
    }
    if (res && (pos < nch)) {
        res = validate_ntype(CHILD(tree, pos), NAME);
        if (res && (strcmp(STR(CHILD(tree, pos)), "finally") == 0))
            res = (validate_numnodes(tree, 6, "try/finally")
                   && validate_colon(CHILD(tree, 4))
                   && validate_suite(CHILD(tree, 5)));
        else if (res) {
            if (nch == (pos + 3)) {
                res = ((strcmp(STR(CHILD(tree, pos)), "except") == 0)
                       || (strcmp(STR(CHILD(tree, pos)), "else") == 0));
                if (!res)
                    err_string("Illegal trailing triple in try statement.");
            }
            else if (nch == (pos + 6)) {
                res = (validate_name(CHILD(tree, pos), "except")
                       && validate_colon(CHILD(tree, pos + 1))
                       && validate_suite(CHILD(tree, pos + 2))
                       && validate_name(CHILD(tree, pos + 3), "else"));
            }
            else
                res = validate_numnodes(tree, pos + 3, "try/except");
        }
    }
    return (res);
}


static int
validate_except_clause(node *tree)
{
    int nch = NCH(tree);
    int res = (validate_ntype(tree, except_clause)
               && ((nch == 1) || (nch == 2) || (nch == 4))
               && validate_name(CHILD(tree, 0), "except"));

    if (res && (nch > 1))
        res = validate_test(CHILD(tree, 1));
    if (res && (nch == 4))
        res = (validate_comma(CHILD(tree, 2))
               && validate_test(CHILD(tree, 3)));

    return (res);
}


static int
validate_test(node *tree)
{
    int nch = NCH(tree);
    int res = validate_ntype(tree, test) && is_odd(nch);

    if (res && (TYPE(CHILD(tree, 0)) == lambdef))
        res = ((nch == 1)
               && validate_lambdef(CHILD(tree, 0)));
    else if (res) {
        int pos;
        res = validate_and_test(CHILD(tree, 0));
        for (pos = 1; res && (pos < nch); pos += 2)
            res = (validate_name(CHILD(tree, pos), "or")
                   && validate_and_test(CHILD(tree, pos + 1)));
    }
    return (res);
}


static int
validate_and_test(node *tree)
{
    int pos;
    int nch = NCH(tree);
    int res = (validate_ntype(tree, and_test)
               && is_odd(nch)
               && validate_not_test(CHILD(tree, 0)));

    for (pos = 1; res && (pos < nch); pos += 2)
        res = (validate_name(CHILD(tree, pos), "and")
               && validate_not_test(CHILD(tree, 0)));

    return (res);
}


static int
validate_not_test(node *tree)
{
    int nch = NCH(tree);
    int res = validate_ntype(tree, not_test) && ((nch == 1) || (nch == 2));

    if (res) {
        if (nch == 2)
            res = (validate_name(CHILD(tree, 0), "not")
                   && validate_not_test(CHILD(tree, 1)));
        else if (nch == 1)
            res = validate_comparison(CHILD(tree, 0));
    }
    return (res);
}


static int
validate_comparison(node *tree)
{
    int pos;
    int nch = NCH(tree);
    int res = (validate_ntype(tree, comparison)
               && is_odd(nch)
               && validate_expr(CHILD(tree, 0)));

    for (pos = 1; res && (pos < nch); pos += 2)
        res = (validate_comp_op(CHILD(tree, pos))
               && validate_expr(CHILD(tree, pos + 1)));

    return (res);
}


static int
validate_comp_op(node *tree)
{
    int res = 0;
    int nch = NCH(tree);

    if (!validate_ntype(tree, comp_op))
        return (0);
    if (nch == 1) {
        /*
         *  Only child will be a terminal with a well-defined symbolic name
         *  or a NAME with a string of either 'is' or 'in'
         */
        tree = CHILD(tree, 0);
        switch (TYPE(tree)) {
            case LESS:
            case GREATER:
            case EQEQUAL:
            case EQUAL:
            case LESSEQUAL:
            case GREATEREQUAL:
            case NOTEQUAL:
              res = 1;
              break;
            case NAME:
              res = ((strcmp(STR(tree), "in") == 0)
                     || (strcmp(STR(tree), "is") == 0));
              if (!res) {
                  char buff[128];
                  (void) sprintf(buff, "Illegal operator: '%s'.", STR(tree));
                  err_string(buff);
              }
              break;
          default:
              err_string("Illegal comparison operator type.");
              break;
        }
    }
    else if ((res = validate_numnodes(tree, 2, "comp_op")) != 0) {
        res = (validate_ntype(CHILD(tree, 0), NAME)
               && validate_ntype(CHILD(tree, 1), NAME)
               && (((strcmp(STR(CHILD(tree, 0)), "is") == 0)
                    && (strcmp(STR(CHILD(tree, 1)), "not") == 0))
                   || ((strcmp(STR(CHILD(tree, 0)), "not") == 0)
                       && (strcmp(STR(CHILD(tree, 1)), "in") == 0))));
        if (!res && !PyErr_Occurred())
            err_string("Unknown comparison operator.");
    }
    return (res);
}


static int
validate_expr(node *tree)
{
    int j;
    int nch = NCH(tree);
    int res = (validate_ntype(tree, expr)
               && is_odd(nch)
               && validate_xor_expr(CHILD(tree, 0)));

    for (j = 2; res && (j < nch); j += 2)
        res = (validate_xor_expr(CHILD(tree, j))
               && validate_vbar(CHILD(tree, j - 1)));

    return (res);
}


static int
validate_xor_expr(node *tree)
{
    int j;
    int nch = NCH(tree);
    int res = (validate_ntype(tree, xor_expr)
               && is_odd(nch)
               && validate_and_expr(CHILD(tree, 0)));

    for (j = 2; res && (j < nch); j += 2)
        res = (validate_circumflex(CHILD(tree, j - 1))
               && validate_and_expr(CHILD(tree, j)));

    return (res);
}


static int
validate_and_expr(node *tree)
{
    int pos;
    int nch = NCH(tree);
    int res = (validate_ntype(tree, and_expr)
               && is_odd(nch)
               && validate_shift_expr(CHILD(tree, 0)));

    for (pos = 1; res && (pos < nch); pos += 2)
        res = (validate_ampersand(CHILD(tree, pos))
               && validate_shift_expr(CHILD(tree, pos + 1)));

    return (res);
}


static int
validate_chain_two_ops(tree, termvalid, op1, op2)
     node *tree;
     int (*termvalid)();
     int op1;
     int op2;
 {
    int pos = 1;
    int nch = NCH(tree);
    int res = (is_odd(nch)
               && (*termvalid)(CHILD(tree, 0)));

    for ( ; res && (pos < nch); pos += 2) {
        if (TYPE(CHILD(tree, pos)) != op1)
            res = validate_ntype(CHILD(tree, pos), op2);
        if (res)
            res = (*termvalid)(CHILD(tree, pos + 1));
    }
    return (res);
}


static int
validate_shift_expr(node *tree)
{
    return (validate_ntype(tree, shift_expr)
            && validate_chain_two_ops(tree, validate_arith_expr,
                                      LEFTSHIFT, RIGHTSHIFT));
}


static int
validate_arith_expr(node *tree)
{
    return (validate_ntype(tree, arith_expr)
            && validate_chain_two_ops(tree, validate_term, PLUS, MINUS));
}


static int
validate_term(node *tree)
{
    int pos = 1;
    int nch = NCH(tree);
    int res = (validate_ntype(tree, term)
               && is_odd(nch)
               && validate_factor(CHILD(tree, 0)));

    for ( ; res && (pos < nch); pos += 2)
        res = (((TYPE(CHILD(tree, pos)) == STAR)
               || (TYPE(CHILD(tree, pos)) == SLASH)
               || (TYPE(CHILD(tree, pos)) == PERCENT))
               && validate_factor(CHILD(tree, pos + 1)));

    return (res);
}


/*  factor:
 *
 *  factor: ('+'|'-'|'~') factor | power
 */
static int
validate_factor(node *tree)
{
    int nch = NCH(tree);
    int res = (validate_ntype(tree, factor)
               && (((nch == 2)
                    && ((TYPE(CHILD(tree, 0)) == PLUS)
                        || (TYPE(CHILD(tree, 0)) == MINUS)
                        || (TYPE(CHILD(tree, 0)) == TILDE))
                    && validate_factor(CHILD(tree, 1)))
                   || ((nch == 1)
                       && validate_power(CHILD(tree, 0)))));
    return (res);
}


/*  power:
 *
 *  power: atom trailer* ('**' factor)*
 */
static int
validate_power(node *tree)
{
    int pos = 1;
    int nch = NCH(tree);
    int res = (validate_ntype(tree, power) && (nch >= 1)
               && validate_atom(CHILD(tree, 0)));

    while (res && (pos < nch) && (TYPE(CHILD(tree, pos)) == trailer))
        res = validate_trailer(CHILD(tree, pos++));
    if (res && (pos < nch)) {
        if (!is_even(nch - pos)) {
            err_string("Illegal number of nodes for 'power'.");
            return (0);
        }
        for ( ; res && (pos < (nch - 1)); pos += 2)
            res = (validate_doublestar(CHILD(tree, pos))
                   && validate_factor(CHILD(tree, pos + 1)));
    }
    return (res);
}


static int
validate_atom(node *tree)
{
    int pos;
    int nch = NCH(tree);
    int res = validate_ntype(tree, atom) && (nch >= 1);

    if (res) {
        switch (TYPE(CHILD(tree, 0))) {
          case LPAR:
            res = ((nch <= 3)
                   && (validate_rparen(CHILD(tree, nch - 1))));

            if (res && (nch == 3))
                res = validate_testlist(CHILD(tree, 1));
            break;
          case LSQB:
            res = ((nch <= 3)
                   && validate_ntype(CHILD(tree, nch - 1), RSQB));

            if (res && (nch == 3))
                res = validate_testlist(CHILD(tree, 1));
            break;
          case LBRACE:
            res = ((nch <= 3)
                   && validate_ntype(CHILD(tree, nch - 1), RBRACE));

            if (res && (nch == 3))
                res = validate_dictmaker(CHILD(tree, 1));
            break;
          case BACKQUOTE:
            res = ((nch == 3)
                   && validate_testlist(CHILD(tree, 1))
                   && validate_ntype(CHILD(tree, 2), BACKQUOTE));
            break;
          case NAME:
          case NUMBER:
            res = (nch == 1);
            break;
          case STRING:
            for (pos = 1; res && (pos < nch); ++pos)
                res = validate_ntype(CHILD(tree, pos), STRING);
            break;
          default:
            res = 0;
            break;
        }
    }
    return (res);
}


/*  funcdef:
 *      'def' NAME parameters ':' suite
 *
 */
static int
validate_funcdef(node *tree)
{
    return (validate_ntype(tree, funcdef)
            && validate_numnodes(tree, 5, "funcdef")
            && validate_name(CHILD(tree, 0), "def")
            && validate_ntype(CHILD(tree, 1), NAME)
            && validate_colon(CHILD(tree, 3))
            && validate_parameters(CHILD(tree, 2))
            && validate_suite(CHILD(tree, 4)));
}


static int
validate_lambdef(node *tree)
{
    int nch = NCH(tree);
    int res = (validate_ntype(tree, lambdef)
               && ((nch == 3) || (nch == 4))
               && validate_name(CHILD(tree, 0), "lambda")
               && validate_colon(CHILD(tree, nch - 2))
               && validate_test(CHILD(tree, nch - 1)));

    if (res && (nch == 4))
        res = validate_varargslist(CHILD(tree, 1));
    else if (!res && !PyErr_Occurred())
        (void) validate_numnodes(tree, 3, "lambdef");

    return (res);
}


/*  arglist:
 *
 *  (argument ',')* (argument* [','] | '*' test [',' '**' test] | '**' test)
 */
static int
validate_arglist(node *tree)
{
    int nch = NCH(tree);
    int i, ok;
    node *last;

    if (nch <= 0)
        /* raise the right error from having an invalid number of children */
        return validate_numnodes(tree, nch + 1, "arglist");

    last = CHILD(tree, nch - 1);
    if (TYPE(last) == test) {
        /* Extended call syntax introduced in Python 1.6 has been used;
         * validate and strip that off and continue;
         * adjust nch to perform the cut, and ensure resulting nch is even
         * (validation of the first part doesn't require that).
         */
        if (nch < 2) {
            validate_numnodes(tree, nch + 1, "arglist");
            return 0;
        }
        ok = validate_test(last);
        if (ok) {
            node *prev = CHILD(tree, nch - 2);
            /* next must be '*' or '**' */
            if (validate_doublestar(prev)) {
                nch -= 2;
                if (nch >= 3) {
                    /* may include:  '*' test ',' */
                    last = CHILD(tree, nch - 1);
                    prev = CHILD(tree, nch - 2);
                    if (TYPE(prev) == test) {
                        ok = validate_comma(last)
                             && validate_test(prev)
                             && validate_star(CHILD(tree, nch - 3));
                        if (ok)
                            nch -= 3;
                    }
                    /* otherwise, nothing special */
                }
            }
            else {
                /* must be only:  '*' test */
                PyErr_Clear();
                ok = validate_star(prev);
                nch -= 2;
            }
            if (ok && is_odd(nch)) {
                /* Illegal number of nodes before extended call syntax;
                 * validation of the "normal" arguments does not require
                 * a trailing comma, but requiring an even number of
                 * children will effect the same requirement.
                 */
                return validate_numnodes(tree, nch + 1, "arglist");
            }
        }
    }
    /* what remains must be:  (argument ",")* [argument [","]] */
    i = 0;
    while (ok && nch - i >= 2) {
        ok = validate_argument(CHILD(tree, i))
             && validate_comma(CHILD(tree, i + 1));
        i += 2;
    }
    if (ok && i < nch) {
        ok = validate_comma(CHILD(tree, i));
        ++i;
    }
    if (i != nch) {
        /* internal error! */
        ok = 0;
        err_string("arglist: internal error; nch != i");
    }
    return (ok);
}



/*  argument:
 *
 *  [test '='] test
 */
static int
validate_argument(node *tree)
{
    int nch = NCH(tree);
    int res = (validate_ntype(tree, argument)
               && ((nch == 1) || (nch == 3))
               && validate_test(CHILD(tree, 0)));

    if (res && (nch == 3))
        res = (validate_equal(CHILD(tree, 1))
               && validate_test(CHILD(tree, 2)));

    return (res);
}



/*  trailer:
 *
 *  '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME
 */
static int
validate_trailer(node *tree)
{
    int nch = NCH(tree);
    int res = validate_ntype(tree, trailer) && ((nch == 2) || (nch == 3));

    if (res) {
        switch (TYPE(CHILD(tree, 0))) {
          case LPAR:
            res = validate_rparen(CHILD(tree, nch - 1));
            if (res && (nch == 3))
                res = validate_arglist(CHILD(tree, 1));
            break;
          case LSQB:
            res = (validate_numnodes(tree, 3, "trailer")
                   && validate_subscriptlist(CHILD(tree, 1))
                   && validate_ntype(CHILD(tree, 2), RSQB));
            break;
          case DOT:
            res = (validate_numnodes(tree, 2, "trailer")
                   && validate_ntype(CHILD(tree, 1), NAME));
            break;
          default:
            res = 0;
            break;
        }
    }
    else {
        (void) validate_numnodes(tree, 2, "trailer");
    }
    return (res);
}


/*  subscriptlist:
 *
 *  subscript (',' subscript)* [',']
 */
static int
validate_subscriptlist(node *tree)
{
    return (validate_repeating_list(tree, subscriptlist,
                                    validate_subscript, "subscriptlist"));
}


/*  subscript:
 *
 *  '.' '.' '.' | test | [test] ':' [test] [sliceop]
 */
static int
validate_subscript(node *tree)
{
    int offset = 0;
    int nch = NCH(tree);
    int res = validate_ntype(tree, subscript) && (nch >= 1) && (nch <= 4);

    if (!res) {
        if (!PyErr_Occurred())
            err_string("invalid number of arguments for subscript node");
        return (0);
    }
    if (TYPE(CHILD(tree, 0)) == DOT)
        /* take care of ('.' '.' '.') possibility */
        return (validate_numnodes(tree, 3, "subscript")
                && validate_dot(CHILD(tree, 0))
                && validate_dot(CHILD(tree, 1))
                && validate_dot(CHILD(tree, 2)));
    if (nch == 1) {
        if (TYPE(CHILD(tree, 0)) == test)
            res = validate_test(CHILD(tree, 0));
        else
            res = validate_colon(CHILD(tree, 0));
        return (res);
    }
    /*  Must be [test] ':' [test] [sliceop],
     *  but at least one of the optional components will
     *  be present, but we don't know which yet.
     */
    if ((TYPE(CHILD(tree, 0)) != COLON) || (nch == 4)) {
        res = validate_test(CHILD(tree, 0));
        offset = 1;
    }
    if (res)
        res = validate_colon(CHILD(tree, offset));
    if (res) {
        int rem = nch - ++offset;
        if (rem) {
            if (TYPE(CHILD(tree, offset)) == test) {
                res = validate_test(CHILD(tree, offset));
                ++offset;
                --rem;
            }
            if (res && rem)
                res = validate_sliceop(CHILD(tree, offset));
        }
    }
    return (res);
}


static int
validate_sliceop(node *tree)
{
    int nch = NCH(tree);
    int res = ((nch == 1) || validate_numnodes(tree, 2, "sliceop"))
              && validate_ntype(tree, sliceop);
    if (!res && !PyErr_Occurred()) {
        res = validate_numnodes(tree, 1, "sliceop");
    }
    if (res)
        res = validate_colon(CHILD(tree, 0));
    if (res && (nch == 2))
        res = validate_test(CHILD(tree, 1));

    return (res);
}


static int
validate_exprlist(node *tree)
{
    return (validate_repeating_list(tree, exprlist,
                                    validate_expr, "exprlist"));
}


static int
validate_dictmaker(node *tree)
{
    int nch = NCH(tree);
    int res = (validate_ntype(tree, dictmaker)
               && (nch >= 3)
               && validate_test(CHILD(tree, 0))
               && validate_colon(CHILD(tree, 1))
               && validate_test(CHILD(tree, 2)));

    if (res && ((nch % 4) == 0))
        res = validate_comma(CHILD(tree, --nch));
    else if (res)
        res = ((nch % 4) == 3);

    if (res && (nch > 3)) {
        int pos = 3;
        /*  ( ',' test ':' test )*  */
        while (res && (pos < nch)) {
            res = (validate_comma(CHILD(tree, pos))
                   && validate_test(CHILD(tree, pos + 1))
                   && validate_colon(CHILD(tree, pos + 2))
                   && validate_test(CHILD(tree, pos + 3)));
            pos += 4;
        }
    }
    return (res);
}


static int
validate_eval_input(node *tree)
{
    int pos;
    int nch = NCH(tree);
    int res = (validate_ntype(tree, eval_input)
               && (nch >= 2)
               && validate_testlist(CHILD(tree, 0))
               && validate_ntype(CHILD(tree, nch - 1), ENDMARKER));

    for (pos = 1; res && (pos < (nch - 1)); ++pos)
        res = validate_ntype(CHILD(tree, pos), NEWLINE);

    return (res);
}


static int
validate_node(node *tree)
{
    int   nch  = 0;                     /* num. children on current node  */
    int   res  = 1;                     /* result value                   */
    node* next = 0;                     /* node to process after this one */

    while (res & (tree != 0)) {
        nch  = NCH(tree);
        next = 0;
        switch (TYPE(tree)) {
            /*
             *  Definition nodes.
             */
          case funcdef:
            res = validate_funcdef(tree);
            break;
          case classdef:
            res = validate_class(tree);
            break;
            /*
             *  "Trivial" parse tree nodes.
             *  (Why did I call these trivial?)
             */
          case stmt:
            res = validate_stmt(tree);
            break;
          case small_stmt:
            /*
             *  expr_stmt | print_stmt  | del_stmt | pass_stmt | flow_stmt
             *  | import_stmt | global_stmt | exec_stmt | assert_stmt
             */
            res = validate_small_stmt(tree);
            break;
          case flow_stmt:
            res  = (validate_numnodes(tree, 1, "flow_stmt")
                    && ((TYPE(CHILD(tree, 0)) == break_stmt)
                        || (TYPE(CHILD(tree, 0)) == continue_stmt)
                        || (TYPE(CHILD(tree, 0)) == return_stmt)
                        || (TYPE(CHILD(tree, 0)) == raise_stmt)));
            if (res)
                next = CHILD(tree, 0);
            else if (nch == 1)
                err_string("Illegal flow_stmt type.");
            break;
            /*
             *  Compound statements.
             */
          case simple_stmt:
            res = validate_simple_stmt(tree);
            break;
          case compound_stmt:
            res = validate_compound_stmt(tree);
            break;
            /*
             *  Fundemental statements.
             */
          case expr_stmt:
            res = validate_expr_stmt(tree);
            break;
          case print_stmt:
            res = validate_print_stmt(tree);
            break;
          case del_stmt:
            res = validate_del_stmt(tree);
            break;
          case pass_stmt:
            res = (validate_numnodes(tree, 1, "pass")
                   && validate_name(CHILD(tree, 0), "pass"));
            break;
          case break_stmt:
            res = (validate_numnodes(tree, 1, "break")
                   && validate_name(CHILD(tree, 0), "break"));
            break;
          case continue_stmt:
            res = (validate_numnodes(tree, 1, "continue")
                   && validate_name(CHILD(tree, 0), "continue"));
            break;
          case return_stmt:
            res = validate_return_stmt(tree);
            break;
          case raise_stmt:
            res = validate_raise_stmt(tree);
            break;
          case import_stmt:
            res = validate_import_stmt(tree);
            break;
          case global_stmt:
            res = validate_global_stmt(tree);
            break;
          case exec_stmt:
            res = validate_exec_stmt(tree);
            break;
          case assert_stmt:
            res = validate_assert_stmt(tree);
            break;
          case if_stmt:
            res = validate_if(tree);
            break;
          case while_stmt:
            res = validate_while(tree);
            break;
          case for_stmt:
            res = validate_for(tree);
            break;
          case try_stmt:
            res = validate_try(tree);
            break;
          case suite:
            res = validate_suite(tree);
            break;
            /*
             *  Expression nodes.
             */
          case testlist:
            res = validate_testlist(tree);
            break;
          case test:
            res = validate_test(tree);
            break;
          case and_test:
            res = validate_and_test(tree);
            break;
          case not_test:
            res = validate_not_test(tree);
            break;
          case comparison:
            res = validate_comparison(tree);
            break;
          case exprlist:
            res = validate_exprlist(tree);
            break;
          case comp_op:
            res = validate_comp_op(tree);
            break;
          case expr:
            res = validate_expr(tree);
            break;
          case xor_expr:
            res = validate_xor_expr(tree);
            break;
          case and_expr:
            res = validate_and_expr(tree);
            break;
          case shift_expr:
            res = validate_shift_expr(tree);
            break;
          case arith_expr:
            res = validate_arith_expr(tree);
            break;
          case term:
            res = validate_term(tree);
            break;
          case factor:
            res = validate_factor(tree);
            break;
          case power:
            res = validate_power(tree);
            break;
          case atom:
            res = validate_atom(tree);
            break;

          default:
            /* Hopefully never reached! */
            err_string("Unrecogniged node type.");
            res = 0;
            break;
        }
        tree = next;
    }
    return (res);
}


static int
validate_expr_tree(node *tree)
{
    int res = validate_eval_input(tree);

    if (!res && !PyErr_Occurred())
        err_string("Could not validate expression tuple.");

    return (res);
}


/*  file_input:
 *      (NEWLINE | stmt)* ENDMARKER
 */
static int
validate_file_input(node *tree)
{
    int j   = 0;
    int nch = NCH(tree) - 1;
    int res = ((nch >= 0)
               && validate_ntype(CHILD(tree, nch), ENDMARKER));

    for ( ; res && (j < nch); ++j) {
        if (TYPE(CHILD(tree, j)) == stmt)
            res = validate_stmt(CHILD(tree, j));
        else
            res = validate_newline(CHILD(tree, j));
    }
    /*  This stays in to prevent any internal failues from getting to the
     *  user.  Hopefully, this won't be needed.  If a user reports getting
     *  this, we have some debugging to do.
     */
    if (!res && !PyErr_Occurred())
        err_string("VALIDATION FAILURE: report this to the maintainer!.");

    return (res);
}


static PyObject*
pickle_constructor = NULL;


static PyObject*
parser__pickler(PyObject *self, PyObject *args)
{
    NOTE(ARGUNUSED(self))
    PyObject *result = NULL;
    PyObject *ast = NULL;
    PyObject *empty_dict = NULL;

    if (PyArg_ParseTuple(args, "O!:_pickler", &PyAST_Type, &ast)) {
        PyObject *newargs;
        PyObject *tuple;

        if ((empty_dict = PyDict_New()) == NULL)
            goto finally;
        if ((newargs = Py_BuildValue("Oi", ast, 1)) == NULL)
            goto finally;
        tuple = parser_ast2tuple((PyAST_Object*)NULL, newargs, empty_dict);
        if (tuple != NULL) {
            result = Py_BuildValue("O(O)", pickle_constructor, tuple);
            Py_DECREF(tuple);
        }
        Py_DECREF(empty_dict);
        Py_DECREF(newargs);
    }
  finally:
    Py_XDECREF(empty_dict);

    return (result);
}


/*  Functions exported by this module.  Most of this should probably
 *  be converted into an AST object with methods, but that is better
 *  done directly in Python, allowing subclasses to be created directly.
 *  We'd really have to write a wrapper around it all anyway to allow
 *  inheritance.
 */
static PyMethodDef parser_functions[] =  {
    {"ast2tuple",       (PyCFunction)parser_ast2tuple,  PUBLIC_METHOD_TYPE,
        "Creates a tuple-tree representation of an AST."},
    {"ast2list",        (PyCFunction)parser_ast2list,   PUBLIC_METHOD_TYPE,
        "Creates a list-tree representation of an AST."},
    {"compileast",      (PyCFunction)parser_compileast, PUBLIC_METHOD_TYPE,
        "Compiles an AST object into a code object."},
    {"expr",            (PyCFunction)parser_expr,       PUBLIC_METHOD_TYPE,
        "Creates an AST object from an expression."},
    {"isexpr",          (PyCFunction)parser_isexpr,     PUBLIC_METHOD_TYPE,
        "Determines if an AST object was created from an expression."},
    {"issuite",         (PyCFunction)parser_issuite,    PUBLIC_METHOD_TYPE,
        "Determines if an AST object was created from a suite."},
    {"suite",           (PyCFunction)parser_suite,      PUBLIC_METHOD_TYPE,
        "Creates an AST object from a suite."},
    {"sequence2ast",    (PyCFunction)parser_tuple2ast,  PUBLIC_METHOD_TYPE,
        "Creates an AST object from a tree representation."},
    {"tuple2ast",       (PyCFunction)parser_tuple2ast,  PUBLIC_METHOD_TYPE,
        "Creates an AST object from a tree representation."},

    /* private stuff: support pickle module */
    {"_pickler",        (PyCFunction)parser__pickler,   METH_VARARGS,
        "Returns the pickle magic to allow ast objects to be pickled."},

    {NULL, NULL, 0, NULL}
    };


DL_EXPORT(void)
initparser()
 {
    PyObject* module;
    PyObject* dict;
        
    PyAST_Type.ob_type = &PyType_Type;
    module = Py_InitModule("parser", parser_functions);
    dict = PyModule_GetDict(module);

    if (parser_error == 0)
        parser_error = PyErr_NewException("parser.ParserError", NULL, NULL);
    else
        puts("parser module initialized more than once!");

    if ((parser_error == 0)
        || (PyDict_SetItemString(dict, "ParserError", parser_error) != 0)) {
        /*
         *  This is serious.
         */
        Py_FatalError("can't define parser.ParserError");
    }
    /*
     *  Nice to have, but don't cry if we fail.
     */
    Py_INCREF(&PyAST_Type);
    PyDict_SetItemString(dict, "ASTType", (PyObject*)&PyAST_Type);

    PyDict_SetItemString(dict, "__copyright__",
                         PyString_FromString(parser_copyright_string));
    PyDict_SetItemString(dict, "__doc__",
                         PyString_FromString(parser_doc_string));
    PyDict_SetItemString(dict, "__version__",
                         PyString_FromString(parser_version_string));

    /* register to support pickling */
    module = PyImport_ImportModule("copy_reg");
    if (module != NULL) {
        PyObject *func, *pickler;

        func = PyObject_GetAttrString(module, "pickle");
        pickle_constructor = PyDict_GetItemString(dict, "sequence2ast");
        pickler = PyDict_GetItemString(dict, "_pickler");
        Py_XINCREF(pickle_constructor);
        if ((func != NULL) && (pickle_constructor != NULL)
            && (pickler != NULL)) {
            PyObject *res;

            res = PyObject_CallFunction(
                    func, "OOO", &PyAST_Type, pickler, pickle_constructor);
            Py_XDECREF(res);
        }
        Py_XDECREF(func);
        Py_DECREF(module);
    }
}