| /* Parser implementation */ |
| |
| /* For a description, see the comments at end of this file */ |
| |
| /* XXX To do: error recovery */ |
| |
| #include "pgenheaders.h" |
| #include "assert.h" |
| #include "token.h" |
| #include "grammar.h" |
| #include "node.h" |
| #include "parser.h" |
| #include "errcode.h" |
| |
| |
| #ifdef DEBUG |
| extern int debugging; |
| #define D(x) if (!debugging); else x |
| #else |
| #define D(x) |
| #endif |
| |
| |
| /* STACK DATA TYPE */ |
| |
| static void s_reset PROTO((stack *)); |
| |
| static void |
| s_reset(s) |
| stack *s; |
| { |
| s->s_top = &s->s_base[MAXSTACK]; |
| } |
| |
| #define s_empty(s) ((s)->s_top == &(s)->s_base[MAXSTACK]) |
| |
| static int s_push PROTO((stack *, dfa *, node *)); |
| |
| static int |
| s_push(s, d, parent) |
| register stack *s; |
| dfa *d; |
| node *parent; |
| { |
| register stackentry *top; |
| if (s->s_top == s->s_base) { |
| fprintf(stderr, "s_push: parser stack overflow\n"); |
| return -1; |
| } |
| top = --s->s_top; |
| top->s_dfa = d; |
| top->s_parent = parent; |
| top->s_state = 0; |
| return 0; |
| } |
| |
| #ifdef DEBUG |
| |
| static void s_pop PROTO((stack *)); |
| |
| static void |
| s_pop(s) |
| register stack *s; |
| { |
| if (s_empty(s)) { |
| fprintf(stderr, "s_pop: parser stack underflow -- FATAL\n"); |
| abort(); |
| } |
| s->s_top++; |
| } |
| |
| #else /* !DEBUG */ |
| |
| #define s_pop(s) (s)->s_top++ |
| |
| #endif |
| |
| |
| /* PARSER CREATION */ |
| |
| parser_state * |
| newparser(g, start) |
| grammar *g; |
| int start; |
| { |
| parser_state *ps; |
| |
| if (!g->g_accel) |
| addaccelerators(g); |
| ps = NEW(parser_state, 1); |
| if (ps == NULL) |
| return NULL; |
| ps->p_grammar = g; |
| ps->p_tree = newtree(start); |
| if (ps->p_tree == NULL) { |
| DEL(ps); |
| return NULL; |
| } |
| s_reset(&ps->p_stack); |
| (void) s_push(&ps->p_stack, finddfa(g, start), ps->p_tree); |
| return ps; |
| } |
| |
| void |
| delparser(ps) |
| parser_state *ps; |
| { |
| /* NB If you want to save the parse tree, |
| you must set p_tree to NULL before calling delparser! */ |
| freetree(ps->p_tree); |
| DEL(ps); |
| } |
| |
| |
| /* PARSER STACK OPERATIONS */ |
| |
| static int shift PROTO((stack *, int, char *, int, int)); |
| |
| static int |
| shift(s, type, str, newstate, lineno) |
| register stack *s; |
| int type; |
| char *str; |
| int newstate; |
| int lineno; |
| { |
| assert(!s_empty(s)); |
| if (addchild(s->s_top->s_parent, type, str, lineno) == NULL) { |
| fprintf(stderr, "shift: no mem in addchild\n"); |
| return -1; |
| } |
| s->s_top->s_state = newstate; |
| return 0; |
| } |
| |
| static int push PROTO((stack *, int, dfa *, int, int)); |
| |
| static int |
| push(s, type, d, newstate, lineno) |
| register stack *s; |
| int type; |
| dfa *d; |
| int newstate; |
| int lineno; |
| { |
| register node *n; |
| n = s->s_top->s_parent; |
| assert(!s_empty(s)); |
| if (addchild(n, type, (char *)NULL, lineno) == NULL) { |
| fprintf(stderr, "push: no mem in addchild\n"); |
| return -1; |
| } |
| s->s_top->s_state = newstate; |
| return s_push(s, d, CHILD(n, NCH(n)-1)); |
| } |
| |
| |
| /* PARSER PROPER */ |
| |
| static int classify PROTO((grammar *, int, char *)); |
| |
| static int |
| classify(g, type, str) |
| grammar *g; |
| register int type; |
| char *str; |
| { |
| register int n = g->g_ll.ll_nlabels; |
| |
| if (type == NAME) { |
| register char *s = str; |
| register label *l = g->g_ll.ll_label; |
| register int i; |
| for (i = n; i > 0; i--, l++) { |
| if (l->lb_type == NAME && l->lb_str != NULL && |
| l->lb_str[0] == s[0] && |
| strcmp(l->lb_str, s) == 0) { |
| D(printf("It's a keyword\n")); |
| return n - i; |
| } |
| } |
| } |
| |
| { |
| register label *l = g->g_ll.ll_label; |
| register int i; |
| for (i = n; i > 0; i--, l++) { |
| if (l->lb_type == type && l->lb_str == NULL) { |
| D(printf("It's a token we know\n")); |
| return n - i; |
| } |
| } |
| } |
| |
| D(printf("Illegal token\n")); |
| return -1; |
| } |
| |
| int |
| addtoken(ps, type, str, lineno) |
| register parser_state *ps; |
| register int type; |
| char *str; |
| int lineno; |
| { |
| register int ilabel; |
| |
| D(printf("Token %s/'%s' ... ", tok_name[type], str)); |
| |
| /* Find out which label this token is */ |
| ilabel = classify(ps->p_grammar, type, str); |
| if (ilabel < 0) |
| return E_SYNTAX; |
| |
| /* Loop until the token is shifted or an error occurred */ |
| for (;;) { |
| /* Fetch the current dfa and state */ |
| register dfa *d = ps->p_stack.s_top->s_dfa; |
| register state *s = &d->d_state[ps->p_stack.s_top->s_state]; |
| |
| D(printf(" DFA '%s', state %d:", |
| d->d_name, ps->p_stack.s_top->s_state)); |
| |
| /* Check accelerator */ |
| if (s->s_lower <= ilabel && ilabel < s->s_upper) { |
| register int x = s->s_accel[ilabel - s->s_lower]; |
| if (x != -1) { |
| if (x & (1<<7)) { |
| /* Push non-terminal */ |
| int nt = (x >> 8) + NT_OFFSET; |
| int arrow = x & ((1<<7)-1); |
| dfa *d1 = finddfa(ps->p_grammar, nt); |
| if (push(&ps->p_stack, nt, d1, |
| arrow, lineno) < 0) { |
| D(printf(" MemError: push.\n")); |
| return E_NOMEM; |
| } |
| D(printf(" Push ...\n")); |
| continue; |
| } |
| |
| /* Shift the token */ |
| if (shift(&ps->p_stack, type, str, |
| x, lineno) < 0) { |
| D(printf(" MemError: shift.\n")); |
| return E_NOMEM; |
| } |
| D(printf(" Shift.\n")); |
| /* Pop while we are in an accept-only state */ |
| while (s = &d->d_state |
| [ps->p_stack.s_top->s_state], |
| s->s_accept && s->s_narcs == 1) { |
| D(printf(" Direct pop.\n")); |
| s_pop(&ps->p_stack); |
| if (s_empty(&ps->p_stack)) { |
| D(printf(" ACCEPT.\n")); |
| return E_DONE; |
| } |
| d = ps->p_stack.s_top->s_dfa; |
| } |
| return E_OK; |
| } |
| } |
| |
| if (s->s_accept) { |
| /* Pop this dfa and try again */ |
| s_pop(&ps->p_stack); |
| D(printf(" Pop ...\n")); |
| if (s_empty(&ps->p_stack)) { |
| D(printf(" Error: bottom of stack.\n")); |
| return E_SYNTAX; |
| } |
| continue; |
| } |
| |
| /* Stuck, report syntax error */ |
| D(printf(" Error.\n")); |
| return E_SYNTAX; |
| } |
| } |
| |
| |
| #ifdef DEBUG |
| |
| /* DEBUG OUTPUT */ |
| |
| void |
| dumptree(g, n) |
| grammar *g; |
| node *n; |
| { |
| int i; |
| |
| if (n == NULL) |
| printf("NIL"); |
| else { |
| label l; |
| l.lb_type = TYPE(n); |
| l.lb_str = TYPE(str); |
| printf("%s", labelrepr(&l)); |
| if (ISNONTERMINAL(TYPE(n))) { |
| printf("("); |
| for (i = 0; i < NCH(n); i++) { |
| if (i > 0) |
| printf(","); |
| dumptree(g, CHILD(n, i)); |
| } |
| printf(")"); |
| } |
| } |
| } |
| |
| void |
| showtree(g, n) |
| grammar *g; |
| node *n; |
| { |
| int i; |
| |
| if (n == NULL) |
| return; |
| if (ISNONTERMINAL(TYPE(n))) { |
| for (i = 0; i < NCH(n); i++) |
| showtree(g, CHILD(n, i)); |
| } |
| else if (ISTERMINAL(TYPE(n))) { |
| printf("%s", tok_name[TYPE(n)]); |
| if (TYPE(n) == NUMBER || TYPE(n) == NAME) |
| printf("(%s)", STR(n)); |
| printf(" "); |
| } |
| else |
| printf("? "); |
| } |
| |
| void |
| printtree(ps) |
| parser_state *ps; |
| { |
| if (debugging) { |
| printf("Parse tree:\n"); |
| dumptree(ps->p_grammar, ps->p_tree); |
| printf("\n"); |
| printf("Tokens:\n"); |
| showtree(ps->p_grammar, ps->p_tree); |
| printf("\n"); |
| } |
| printf("Listing:\n"); |
| listtree(ps->p_tree); |
| printf("\n"); |
| } |
| |
| #endif /* DEBUG */ |
| |
| /* |
| |
| Description |
| ----------- |
| |
| The parser's interface is different than usual: the function addtoken() |
| must be called for each token in the input. This makes it possible to |
| turn it into an incremental parsing system later. The parsing system |
| constructs a parse tree as it goes. |
| |
| A parsing rule is represented as a Deterministic Finite-state Automaton |
| (DFA). A node in a DFA represents a state of the parser; an arc represents |
| a transition. Transitions are either labeled with terminal symbols or |
| with non-terminals. When the parser decides to follow an arc labeled |
| with a non-terminal, it is invoked recursively with the DFA representing |
| the parsing rule for that as its initial state; when that DFA accepts, |
| the parser that invoked it continues. The parse tree constructed by the |
| recursively called parser is inserted as a child in the current parse tree. |
| |
| The DFA's can be constructed automatically from a more conventional |
| language description. An extended LL(1) grammar (ELL(1)) is suitable. |
| Certain restrictions make the parser's life easier: rules that can produce |
| the empty string should be outlawed (there are other ways to put loops |
| or optional parts in the language). To avoid the need to construct |
| FIRST sets, we can require that all but the last alternative of a rule |
| (really: arc going out of a DFA's state) must begin with a terminal |
| symbol. |
| |
| As an example, consider this grammar: |
| |
| expr: term (OP term)* |
| term: CONSTANT | '(' expr ')' |
| |
| The DFA corresponding to the rule for expr is: |
| |
| ------->.---term-->.-------> |
| ^ | |
| | | |
| \----OP----/ |
| |
| The parse tree generated for the input a+b is: |
| |
| (expr: (term: (NAME: a)), (OP: +), (term: (NAME: b))) |
| |
| */ |