From 02a3e9b26725c4e1bd90b43ef3dce7b4409998ce Mon Sep 17 00:00:00 2001
From: Chris Mounce <christophermounce@gmail.com>
Date: Mon, 26 May 2025 22:59:17 -0700
Subject: [PATCH] Add grammar! matching on character ranges

---
 peg_macro/src/lib.rs | 24 +++++++++++++++++++++---
 src/peg/peg.rs       | 24 ++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 3 deletions(-)

diff --git a/peg_macro/src/lib.rs b/peg_macro/src/lib.rs
index f2500eb..4b644a4 100644
--- a/peg_macro/src/lib.rs
+++ b/peg_macro/src/lib.rs
@@ -1,7 +1,9 @@
+use std::ops::RangeInclusive;
+
 use proc_macro::TokenStream;
 use quote::quote;
 use syn::{
-    Ident, LitStr, Token,
+    Ident, LitChar, LitStr, Token,
     parse::{Parse, ParseStream},
     parse_macro_input,
     punctuated::Punctuated,
@@ -20,10 +22,11 @@ enum Term {
     Choice(Vec<Term>),
     Literal(LitStr),
     Optional(Box<Term>),
+    Plus(Box<Term>),
+    Range(RangeInclusive<char>),
     Rule(Ident),
     Sequence(Vec<Term>),
     Star(Box<Term>),
-    Plus(Box<Term>),
 }
 
 impl Parse for Grammar {
@@ -45,12 +48,21 @@ impl Parse for Rule {
 
 impl Parse for Term {
     fn parse(input: ParseStream) -> syn::Result<Self> {
+        fn parse_range(input: ParseStream) -> syn::Result<Term> {
+            let start = input.parse::<LitChar>()?.value();
+            input.parse::<Token![..]>()?;
+            let end = input.parse::<LitChar>()?.value();
+            Ok(Term::Range(start..=end))
+        }
+
         fn parse_atom(input: ParseStream) -> syn::Result<Term> {
             let look = input.lookahead1();
             if look.peek(Ident) {
                 input.parse().map(Term::Rule)
             } else if look.peek(LitStr) {
                 input.parse().map(Term::Literal)
+            } else if look.peek(LitChar) {
+                parse_range(input)
             } else {
                 Err(look.error())
             }
@@ -74,7 +86,7 @@ impl Parse for Term {
 
         fn parse_sequence(input: ParseStream) -> syn::Result<Term> {
             let mut terms = vec![parse_repeat(input)?];
-            while input.peek(Ident) || input.peek(LitStr) {
+            while input.peek(Ident) || input.peek(LitStr) || input.peek(LitChar) {
                 terms.push(parse_repeat(input)?);
             }
             if terms.len() == 1 {
@@ -158,6 +170,12 @@ impl Term {
                     }
                 }
             }
+            Term::Range(range) => {
+                let (lo, hi) = (range.start(), range.end());
+                quote! {
+                    p.range(#lo..=#hi)
+                }
+            }
         }
     }
 }
diff --git a/src/peg/peg.rs b/src/peg/peg.rs
index 624f14a..723418f 100644
--- a/src/peg/peg.rs
+++ b/src/peg/peg.rs
@@ -1,3 +1,5 @@
+use std::ops::RangeInclusive;
+
 pub struct ParseState {
     pub input: String,
     pub offset: usize,
@@ -33,6 +35,16 @@ impl ParseState {
             false
         }
     }
+
+    pub fn range(&mut self, r: RangeInclusive<char>) -> bool {
+        if let Some(next) = self.input[self.offset..].chars().next() {
+            if r.contains(&next) {
+                self.offset += next.len_utf8();
+                return true;
+            }
+        }
+        false
+    }
 }
 
 #[cfg(test)]
@@ -49,6 +61,10 @@ mod tests {
         option = "(" "x"? ")";
         plus = "(" "x"+ ")";
         star = "(" "x"* ")";
+
+        word_head = "_" / 'A'..'Z' / 'a'..'z';
+        word_tail = word_head / '0'..'9';
+        word = "(" word_head word_tail* ")";
     }
 
     fn parse<T: Fn(&mut ParseState) -> bool>(rule: T, s: &str) -> bool {
@@ -81,4 +97,12 @@ mod tests {
         assert!(parse(star, many));
         assert!(parse(plus, many));
     }
+
+    #[test]
+    fn test_ranges() {
+        assert!(parse(word, "(_FooBar)"));
+        assert!(parse(word, "(abc123)"));
+        assert!(!parse(word, "(123abc)"));
+        assert!(!parse(word, "(foo-bar)"));
+    }
 }