Try generating named functions via proc macros

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!");
+    }
+}