Try generating named functions via proc macros

Cargo.lock

@@ -132,6 +132,7 @@ name = "peg_macro"
 version = "0.1.0"
 dependencies = [
  "quote",
+ "syn",
 ]
 
 [[package]]
@@ -217,9 +218,9 @@ checksum = "bbbb5d9659141646ae647b42fe094daf6c6192d1620870b449d9557f748b2daa"
 
 [[package]]
 name = "syn"
-version = "2.0.100"
+version = "2.0.101"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b09a44accad81e1ba1cd74a32461ba89dee89095ba17b32f5d03683b1b1fc2a0"
+checksum = "8ce2b7fc941b3a24138a0a7cf8e858bfc6a992e7978a068a5c760deb0ed43caf"
 dependencies = [
  "proc-macro2",
  "quote",

peg_macro/Cargo.toml

@@ -8,3 +8,4 @@ proc-macro = true
 
 [dependencies]
 quote = "1.0.40"
+syn = "2.0.101"

peg_macro/src/lib.rs

@@ -1,8 +1,39 @@
 use proc_macro::TokenStream;
 use quote::quote;
+use syn::{
+    Ident, Token,
+    parse::{Parse, ParseStream},
+    parse_macro_input,
+    punctuated::Punctuated,
+};
+
+struct Grammar {
+    rules: Punctuated<Rule, Token![;]>,
+}
+
+struct Rule {
+    name: Ident,
+}
+
+impl Parse for Grammar {
+    fn parse(input: ParseStream) -> syn::Result<Self> {
+        Ok(Grammar {
+            rules: Punctuated::parse_terminated(input)?,
+        })
+    }
+}
+
+impl Parse for Rule {
+    fn parse(input: ParseStream) -> syn::Result<Self> {
+        let result = Self {
+            name: input.parse()?,
+        };
+        Ok(result)
+    }
+}
 
 #[proc_macro]
-pub fn grammar(ts: TokenStream) -> TokenStream {
+pub fn grammar_old(ts: TokenStream) -> TokenStream {
     let token = ts.into_iter().next().expect("must have at least one token");
     let result = match token {
         proc_macro::TokenTree::Literal(literal) => {
@@ -25,3 +56,24 @@ pub fn grammar(ts: TokenStream) -> TokenStream {
 
     quote! { println!("Hello, world! {:?}", #result); }.into()
 }
+
+#[proc_macro]
+pub fn grammar(ts: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(ts as Grammar);
+    let fns: Vec<_> = input
+        .rules
+        .iter()
+        .map(|r| {
+            let fn_name = &r.name;
+            quote! {
+                fn #fn_name() -> String {
+                    "I'm a generated function!".into()
+                }
+            }
+        })
+        .collect();
+    quote! {
+        #(#fns)*
+    }
+    .into()
+}

src/main.rs

@@ -6,14 +6,14 @@ mod world;
 
 use anyhow::anyhow;
 use labels::labels::print_labels;
-use peg_macro::grammar;
+use peg_macro::grammar_old;
 use preprocess::eval::Context;
 use std::{env, error::Error, fs, path::PathBuf, process::exit};
 use world::World;
 
 fn main() -> Result<(), Box<dyn Error>> {
-    grammar!(123);
-    grammar!("abc");
+    grammar_old!(123);
+    grammar_old!("abc");
 
     let args: Vec<String> = env::args().collect();
     if args.len() != 2 {

src/peg/peg.rs

@@ -1,6 +1,91 @@
+use peg_macro::grammar;
+
 #[derive(Debug)]
 #[allow(dead_code)]
 pub enum Foo {
     Bar(usize),
     Baz(String),
 }
+
+pub struct ParseState {
+    pub input: String,
+    pub offset: usize,
+}
+
+pub struct Savepoint {
+    offset: usize,
+}
+
+impl ParseState {
+    pub fn new(s: &str) -> Self {
+        Self {
+            input: s.into(),
+            offset: 0,
+        }
+    }
+
+    pub fn save(&self) -> Savepoint {
+        Savepoint {
+            offset: self.offset,
+        }
+    }
+
+    pub fn restore(&mut self, save: Savepoint) {
+        self.offset = save.offset;
+    }
+
+    pub fn literal(&mut self, s: &str) -> bool {
+        if self.input[self.offset..].starts_with(s) {
+            self.offset += s.len();
+            true
+        } else {
+            false
+        }
+    }
+}
+
+fn parse_foo(p: &mut ParseState) -> bool {
+    let save = p.save();
+    if !parse_f(p) {
+        return false;
+    }
+    if !parse_oo(p) {
+        p.restore(save);
+        return false;
+    }
+    true
+}
+
+fn parse_f(p: &mut ParseState) -> bool {
+    p.literal("f")
+}
+
+fn parse_oo(p: &mut ParseState) -> bool {
+    p.literal("oo")
+}
+
+grammar! {
+    generated_this;
+    generated_that;
+}
+
+#[cfg(test)]
+mod tests {
+    use insta::assert_snapshot;
+
+    use super::*;
+
+    #[test]
+    fn test_parser() {
+        let mut p = ParseState::new("foo");
+        assert!(parse_foo(&mut p));
+        let mut p = ParseState::new("fee");
+        assert!(!parse_foo(&mut p));
+    }
+
+    #[test]
+    fn test_generated() {
+        assert_snapshot!(generated_this(), @"I'm a generated function!");
+        assert_snapshot!(generated_that(), @"I'm a generated function!");
+    }
+}