diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
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--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,657 @@
+//! As of Rust 1.30, the language supports user-defined function-like procedural
+//! macros. However these can only be invoked in item position, not in
+//! statements or expressions.
+//!
+//! This crate implements an alternative type of procedural macro that can be
+//! invoked in statement or expression position.
+//!
+//! # Defining procedural macros
+//!
+//! Two crates are required to define a procedural macro.
+//!
+//! ## The implementation crate
+//!
+//! This crate must contain nothing but procedural macros. Private helper
+//! functions and private modules are fine but nothing can be public.
+//!
+//! [> example of an implementation crate][demo-hack-impl]
+//!
+//! Just like you would use a #\[proc_macro\] attribute to define a natively
+//! supported procedural macro, use proc-macro-hack's #\[proc_macro_hack\]
+//! attribute to define a procedural macro that works in expression position.
+//! The function signature is the same as for ordinary function-like procedural
+//! macros.
+//!
+//! ```
+//! extern crate proc_macro;
+//!
+//! use proc_macro::TokenStream;
+//! use proc_macro_hack::proc_macro_hack;
+//! use quote::quote;
+//! use syn::{parse_macro_input, Expr};
+//!
+//! # const IGNORE: &str = stringify! {
+//! #[proc_macro_hack]
+//! # };
+//! pub fn add_one(input: TokenStream) -> TokenStream {
+//!     let expr = parse_macro_input!(input as Expr);
+//!     TokenStream::from(quote! {
+//!         1 + (#expr)
+//!     })
+//! }
+//! #
+//! # fn main() {}
+//! ```
+//!
+//! ## The declaration crate
+//!
+//! This crate is allowed to contain other public things if you need, for
+//! example traits or functions or ordinary macros.
+//!
+//! [> example of a declaration crate][demo-hack]
+//!
+//! Within the declaration crate there needs to be a re-export of your
+//! procedural macro from the implementation crate. The re-export also carries a
+//! \#\[proc_macro_hack\] attribute.
+//!
+//! ```
+//! use proc_macro_hack::proc_macro_hack;
+//!
+//! /// Add one to an expression.
+//! ///
+//! /// (Documentation goes here on the re-export, not in the other crate.)
+//! #[proc_macro_hack]
+//! pub use demo_hack_impl::add_one;
+//! #
+//! # fn main() {}
+//! ```
+//!
+//! Both crates depend on `proc-macro-hack`:
+//!
+//! ```toml
+//! [dependencies]
+//! proc-macro-hack = "0.5"
+//! ```
+//!
+//! Additionally, your implementation crate (but not your declaration crate) is
+//! a proc macro crate:
+//!
+//! ```toml
+//! [lib]
+//! proc-macro = true
+//! ```
+//!
+//! # Using procedural macros
+//!
+//! Users of your crate depend on your declaration crate (not your
+//! implementation crate), then use your procedural macros as usual.
+//!
+//! [> example of a downstream crate][example]
+//!
+//! ```
+//! use demo_hack::add_one;
+//!
+//! fn main() {
+//!     let two = 2;
+//!     let nine = add_one!(two) + add_one!(2 + 3);
+//!     println!("nine = {}", nine);
+//! }
+//! ```
+//!
+//! [demo-hack-impl]: https://github.com/dtolnay/proc-macro-hack/tree/master/demo-hack-impl
+//! [demo-hack]: https://github.com/dtolnay/proc-macro-hack/tree/master/demo-hack
+//! [example]: https://github.com/dtolnay/proc-macro-hack/tree/master/example
+//!
+//! # Limitations
+//!
+//! - Only proc macros in expression position are supported. Proc macros in
+//!   pattern position ([#20]) are not supported.
+//!
+//! - By default, nested invocations are not supported i.e. the code emitted by
+//!   a proc-macro-hack macro invocation cannot contain recursive calls to the
+//!   same proc-macro-hack macro nor calls to any other proc-macro-hack macros.
+//!   Use [`proc-macro-nested`] if you require support for nested invocations.
+//!
+//! - By default, hygiene is structured such that the expanded code can't refer
+//!   to local variables other than those passed by name somewhere in the macro
+//!   input. If your macro must refer to *local* variables that don't get named
+//!   in the macro input, use `#[proc_macro_hack(fake_call_site)]` on the
+//!   re-export in your declaration crate. *Most macros won't need this.*
+//!
+//! [#10]: https://github.com/dtolnay/proc-macro-hack/issues/10
+//! [#20]: https://github.com/dtolnay/proc-macro-hack/issues/20
+//! [`proc-macro-nested`]: https://docs.rs/proc-macro-nested
+
+#![recursion_limit = "512"]
+#![cfg_attr(feature = "cargo-clippy", allow(renamed_and_removed_lints))]
+#![cfg_attr(feature = "cargo-clippy", allow(needless_pass_by_value))]
+
+extern crate proc_macro;
+
+use proc_macro2::{Span, TokenStream, TokenTree};
+use quote::{format_ident, quote, ToTokens};
+use std::fmt::Write;
+use syn::ext::IdentExt;
+use syn::parse::{Parse, ParseStream, Result};
+use syn::{braced, bracketed, parenthesized, parse_macro_input, token, Ident, LitInt, Token};
+
+type Visibility = Option<Token![pub]>;
+
+enum Input {
+    Export(Export),
+    Define(Define),
+}
+
+// pub use demo_hack_impl::{m1, m2 as qrst};
+struct Export {
+    attrs: TokenStream,
+    vis: Visibility,
+    from: Ident,
+    macros: Vec<Macro>,
+}
+
+// pub fn m1(input: TokenStream) -> TokenStream { ... }
+struct Define {
+    attrs: TokenStream,
+    name: Ident,
+    body: TokenStream,
+}
+
+struct Macro {
+    name: Ident,
+    export_as: Ident,
+}
+
+impl Parse for Input {
+    fn parse(input: ParseStream) -> Result<Self> {
+        let ahead = input.fork();
+        parse_attributes(&ahead)?;
+        ahead.parse::<Visibility>()?;
+
+        if ahead.peek(Token![use]) {
+            input.parse().map(Input::Export)
+        } else if ahead.peek(Token![fn]) {
+            input.parse().map(Input::Define)
+        } else {
+            Err(input.error("unexpected input to #[proc_macro_hack]"))
+        }
+    }
+}
+
+impl Parse for Export {
+    fn parse(input: ParseStream) -> Result<Self> {
+        let attrs = input.call(parse_attributes)?;
+        let vis: Visibility = input.parse()?;
+        input.parse::<Token![use]>()?;
+        input.parse::<Option<Token![::]>>()?;
+        let from: Ident = input.parse()?;
+        input.parse::<Token![::]>()?;
+
+        let mut macros = Vec::new();
+        if input.peek(token::Brace) {
+            let content;
+            braced!(content in input);
+            loop {
+                macros.push(content.parse()?);
+                if content.is_empty() {
+                    break;
+                }
+                content.parse::<Token![,]>()?;
+                if content.is_empty() {
+                    break;
+                }
+            }
+        } else {
+            macros.push(input.parse()?);
+        }
+
+        input.parse::<Token![;]>()?;
+        Ok(Export {
+            attrs,
+            vis,
+            from,
+            macros,
+        })
+    }
+}
+
+impl Parse for Define {
+    fn parse(input: ParseStream) -> Result<Self> {
+        let attrs = input.call(parse_attributes)?;
+        let vis: Visibility = input.parse()?;
+        if vis.is_none() {
+            return Err(input.error("functions tagged with `#[proc_macro_hack]` must be `pub`"));
+        }
+
+        input.parse::<Token![fn]>()?;
+        let name: Ident = input.parse()?;
+        let body: TokenStream = input.parse()?;
+        Ok(Define { attrs, name, body })
+    }
+}
+
+impl Parse for Macro {
+    fn parse(input: ParseStream) -> Result<Self> {
+        let name: Ident = input.parse()?;
+        let renamed: Option<Token![as]> = input.parse()?;
+        let export_as = if renamed.is_some() {
+            input.parse()?
+        } else {
+            name.clone()
+        };
+        Ok(Macro { name, export_as })
+    }
+}
+
+fn parse_attributes(input: ParseStream) -> Result<TokenStream> {
+    let mut attrs = TokenStream::new();
+    while input.peek(Token![#]) {
+        let pound: Token![#] = input.parse()?;
+        pound.to_tokens(&mut attrs);
+        let content;
+        let bracket_token = bracketed!(content in input);
+        let content: TokenStream = content.parse()?;
+        bracket_token.surround(&mut attrs, |tokens| content.to_tokens(tokens));
+    }
+    Ok(attrs)
+}
+
+#[proc_macro_attribute]
+pub fn proc_macro_hack(
+    args: proc_macro::TokenStream,
+    input: proc_macro::TokenStream,
+) -> proc_macro::TokenStream {
+    proc_macro::TokenStream::from(match parse_macro_input!(input) {
+        Input::Export(export) => {
+            let args = parse_macro_input!(args as ExportArgs);
+            expand_export(export, args)
+        }
+        Input::Define(define) => {
+            parse_macro_input!(args as DefineArgs);
+            expand_define(define)
+        }
+    })
+}
+
+mod kw {
+    syn::custom_keyword!(derive);
+    syn::custom_keyword!(fake_call_site);
+    syn::custom_keyword!(internal_macro_calls);
+    syn::custom_keyword!(support_nested);
+}
+
+struct ExportArgs {
+    support_nested: bool,
+    internal_macro_calls: u16,
+    fake_call_site: bool,
+}
+
+impl Parse for ExportArgs {
+    fn parse(input: ParseStream) -> Result<Self> {
+        let mut args = ExportArgs {
+            support_nested: false,
+            internal_macro_calls: 0,
+            fake_call_site: false,
+        };
+
+        while !input.is_empty() {
+            let ahead = input.lookahead1();
+            if ahead.peek(kw::support_nested) {
+                input.parse::<kw::support_nested>()?;
+                args.support_nested = true;
+            } else if ahead.peek(kw::internal_macro_calls) {
+                input.parse::<kw::internal_macro_calls>()?;
+                input.parse::<Token![=]>()?;
+                let calls = input.parse::<LitInt>()?.base10_parse()?;
+                args.internal_macro_calls = calls;
+            } else if ahead.peek(kw::fake_call_site) {
+                input.parse::<kw::fake_call_site>()?;
+                args.fake_call_site = true;
+            } else {
+                return Err(ahead.error());
+            }
+            if input.is_empty() {
+                break;
+            }
+            input.parse::<Token![,]>()?;
+        }
+
+        Ok(args)
+    }
+}
+
+struct DefineArgs;
+
+impl Parse for DefineArgs {
+    fn parse(_input: ParseStream) -> Result<Self> {
+        Ok(DefineArgs)
+    }
+}
+
+struct EnumHack {
+    token_stream: TokenStream,
+}
+
+impl Parse for EnumHack {
+    fn parse(input: ParseStream) -> Result<Self> {
+        input.parse::<Token![enum]>()?;
+        input.parse::<Ident>()?;
+
+        let braces;
+        braced!(braces in input);
+        braces.parse::<Ident>()?;
+        braces.parse::<Token![=]>()?;
+
+        let parens;
+        parenthesized!(parens in braces);
+        parens.parse::<Ident>()?;
+        parens.parse::<Token![!]>()?;
+
+        let inner;
+        braced!(inner in parens);
+        let token_stream: TokenStream = inner.parse()?;
+
+        parens.parse::<Token![,]>()?;
+        parens.parse::<TokenTree>()?;
+        braces.parse::<Token![.]>()?;
+        braces.parse::<TokenTree>()?;
+        braces.parse::<Token![,]>()?;
+
+        Ok(EnumHack { token_stream })
+    }
+}
+
+#[doc(hidden)]
+#[proc_macro_derive(ProcMacroHack)]
+pub fn enum_hack(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    let inner = parse_macro_input!(input as EnumHack);
+    proc_macro::TokenStream::from(inner.token_stream)
+}
+
+struct FakeCallSite {
+    derive: Ident,
+    rest: TokenStream,
+}
+
+impl Parse for FakeCallSite {
+    fn parse(input: ParseStream) -> Result<Self> {
+        input.parse::<Token![#]>()?;
+        let attr;
+        bracketed!(attr in input);
+        attr.parse::<kw::derive>()?;
+        let path;
+        parenthesized!(path in attr);
+        Ok(FakeCallSite {
+            derive: path.parse()?,
+            rest: input.parse()?,
+        })
+    }
+}
+
+#[doc(hidden)]
+#[proc_macro_attribute]
+pub fn fake_call_site(
+    args: proc_macro::TokenStream,
+    input: proc_macro::TokenStream,
+) -> proc_macro::TokenStream {
+    let args = TokenStream::from(args);
+    let span = match args.into_iter().next() {
+        Some(token) => token.span(),
+        None => return input,
+    };
+
+    let input = parse_macro_input!(input as FakeCallSite);
+    let mut derive = input.derive;
+    derive.set_span(span);
+    let rest = input.rest;
+
+    let expanded = quote! {
+        #[derive(#derive)]
+        #rest
+    };
+
+    proc_macro::TokenStream::from(expanded)
+}
+
+fn expand_export(export: Export, args: ExportArgs) -> TokenStream {
+    let dummy = dummy_name_for_export(&export);
+
+    let attrs = export.attrs;
+    let vis = export.vis;
+    let macro_export = match vis {
+        Some(_) => quote!(#[macro_export]),
+        None => quote!(),
+    };
+    let crate_prefix = vis.map(|_| quote!($crate::));
+    let enum_variant = if args.support_nested {
+        if args.internal_macro_calls == 0 {
+            quote!(Nested)
+        } else {
+            format_ident!("Nested{}", args.internal_macro_calls).to_token_stream()
+        }
+    } else {
+        quote!(Value)
+    };
+
+    let from = export.from;
+    let rules = export
+        .macros
+        .into_iter()
+        .map(|Macro { name, export_as }| {
+            let actual_name = actual_proc_macro_name(&name);
+            let dispatch = dispatch_macro_name(&name);
+            let call_site = call_site_macro_name(&name);
+
+            let export_dispatch = if args.support_nested {
+                quote! {
+                    #[doc(hidden)]
+                    #vis use proc_macro_nested::dispatch as #dispatch;
+                }
+            } else {
+                quote!()
+            };
+
+            let proc_macro_call = if args.support_nested {
+                let extra_bangs = (0..args.internal_macro_calls).map(|_| quote!(!));
+                quote! {
+                    #crate_prefix #dispatch! { ($($proc_macro)*) #(#extra_bangs)* }
+                }
+            } else {
+                quote! {
+                    proc_macro_call!()
+                }
+            };
+
+            let export_call_site = if args.fake_call_site {
+                quote! {
+                    #[doc(hidden)]
+                    #vis use proc_macro_hack::fake_call_site as #call_site;
+                }
+            } else {
+                quote!()
+            };
+
+            let do_derive = if !args.fake_call_site {
+                quote! {
+                    #[derive(#crate_prefix #actual_name)]
+                }
+            } else if crate_prefix.is_some() {
+                quote! {
+                    use #crate_prefix #actual_name;
+                    #[#crate_prefix #call_site ($($proc_macro)*)]
+                    #[derive(#actual_name)]
+                }
+            } else {
+                quote! {
+                    #[#call_site ($($proc_macro)*)]
+                    #[derive(#actual_name)]
+                }
+            };
+
+            quote! {
+                #[doc(hidden)]
+                #vis use #from::#actual_name;
+
+                #export_dispatch
+                #export_call_site
+
+                #attrs
+                #macro_export
+                macro_rules! #export_as {
+                    ($($proc_macro:tt)*) => {{
+                        #do_derive
+                        enum ProcMacroHack {
+                            #enum_variant = (stringify! { $($proc_macro)* }, 0).1,
+                        }
+                        #proc_macro_call
+                    }};
+                }
+            }
+        })
+        .collect();
+
+    wrap_in_enum_hack(dummy, rules)
+}
+
+fn expand_define(define: Define) -> TokenStream {
+    let attrs = define.attrs;
+    let name = define.name;
+    let dummy = actual_proc_macro_name(&name);
+    let body = define.body;
+
+    quote! {
+        mod #dummy {
+            extern crate proc_macro;
+            pub use self::proc_macro::*;
+        }
+
+        #attrs
+        #[proc_macro_derive(#dummy)]
+        pub fn #dummy(input: #dummy::TokenStream) -> #dummy::TokenStream {
+            use std::iter::FromIterator;
+
+            let mut iter = input.into_iter();
+            iter.next().unwrap(); // `enum`
+            iter.next().unwrap(); // `ProcMacroHack`
+
+            let mut braces = match iter.next().unwrap() {
+                #dummy::TokenTree::Group(group) => group.stream().into_iter(),
+                _ => unimplemented!(),
+            };
+            let variant = braces.next().unwrap(); // `Value` or `Nested`
+            let varname = variant.to_string();
+            let support_nested = varname.starts_with("Nested");
+            braces.next().unwrap(); // `=`
+
+            let mut parens = match braces.next().unwrap() {
+                #dummy::TokenTree::Group(group) => group.stream().into_iter(),
+                _ => unimplemented!(),
+            };
+            parens.next().unwrap(); // `stringify`
+            parens.next().unwrap(); // `!`
+
+            let inner = match parens.next().unwrap() {
+                #dummy::TokenTree::Group(group) => group.stream(),
+                _ => unimplemented!(),
+            };
+
+            let output: #dummy::TokenStream = #name(inner.clone());
+
+            fn count_bangs(input: #dummy::TokenStream) -> usize {
+                let mut count = 0;
+                for token in input {
+                    match token {
+                        #dummy::TokenTree::Punct(punct) => {
+                            if punct.as_char() == '!' {
+                                count += 1;
+                            }
+                        }
+                        #dummy::TokenTree::Group(group) => {
+                            count += count_bangs(group.stream());
+                        }
+                        _ => {}
+                    }
+                }
+                count
+            }
+
+            // macro_rules! proc_macro_call {
+            //     () => { #output }
+            // }
+            #dummy::TokenStream::from_iter(vec![
+                #dummy::TokenTree::Ident(
+                    #dummy::Ident::new("macro_rules", #dummy::Span::call_site()),
+                ),
+                #dummy::TokenTree::Punct(
+                    #dummy::Punct::new('!', #dummy::Spacing::Alone),
+                ),
+                #dummy::TokenTree::Ident(
+                    #dummy::Ident::new(
+                        &if support_nested {
+                            let extra_bangs = if varname == "Nested" {
+                                0
+                            } else {
+                                varname["Nested".len()..].parse().unwrap()
+                            };
+                            format!("proc_macro_call_{}", extra_bangs + count_bangs(inner))
+                        } else {
+                            String::from("proc_macro_call")
+                        },
+                        #dummy::Span::call_site(),
+                    ),
+                ),
+                #dummy::TokenTree::Group(
+                    #dummy::Group::new(#dummy::Delimiter::Brace, #dummy::TokenStream::from_iter(vec![
+                        #dummy::TokenTree::Group(
+                            #dummy::Group::new(#dummy::Delimiter::Parenthesis, #dummy::TokenStream::new()),
+                        ),
+                        #dummy::TokenTree::Punct(
+                            #dummy::Punct::new('=', #dummy::Spacing::Joint),
+                        ),
+                        #dummy::TokenTree::Punct(
+                            #dummy::Punct::new('>', #dummy::Spacing::Alone),
+                        ),
+                        #dummy::TokenTree::Group(
+                            #dummy::Group::new(#dummy::Delimiter::Brace, output),
+                        ),
+                    ])),
+                ),
+            ])
+        }
+
+        fn #name #body
+    }
+}
+
+fn actual_proc_macro_name(conceptual: &Ident) -> Ident {
+    format_ident!("proc_macro_hack_{}", conceptual)
+}
+
+fn dispatch_macro_name(conceptual: &Ident) -> Ident {
+    format_ident!("proc_macro_call_{}", conceptual)
+}
+
+fn call_site_macro_name(conceptual: &Ident) -> Ident {
+    format_ident!("proc_macro_fake_call_site_{}", conceptual)
+}
+
+fn dummy_name_for_export(export: &Export) -> String {
+    let mut dummy = String::new();
+    let from = export.from.unraw().to_string();
+    write!(dummy, "_{}{}", from.len(), from).unwrap();
+    for m in &export.macros {
+        let name = m.name.unraw().to_string();
+        write!(dummy, "_{}{}", name.len(), name).unwrap();
+    }
+    dummy
+}
+
+fn wrap_in_enum_hack(dummy: String, inner: TokenStream) -> TokenStream {
+    let dummy = Ident::new(&dummy, Span::call_site());
+    quote! {
+        #[derive(proc_macro_hack::ProcMacroHack)]
+        enum #dummy {
+            Value = (stringify! { #inner }, 0).1,
+        }
+    }
+}