From afae0d0840433c5e9f41d9260c3c1b9b547cfa73 Mon Sep 17 00:00:00 2001
From: Greg Shuflin <greg@everydayimshuflin.com>
Date: Sat, 27 Jan 2024 16:00:29 -0800
Subject: [PATCH] Parser Extension

---
 src/lib.rs | 44 ++++++++++++++++++++++++++++++++++++++------
 1 file changed, 38 insertions(+), 6 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index f0d0478..9f2e596 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -26,6 +26,35 @@ where
     }
 }
 
+pub trait ParserExtension<I, O, E>: Parser<I, O, E> {
+    fn map<F, O2>(self, map_fn: F) -> impl Parser<I, O2, E>
+    where
+        F: Fn(O) -> O2;
+
+    fn to<O2: Clone>(self, item: O2) -> impl Parser<I, O2, E>;
+    fn then<O2, P: Parser<I, O2, E>>(self, next: P) -> impl Parser<I, (O, O2), E>;
+}
+
+impl<T, I, O, E> ParserExtension<I, O, E> for T
+where
+    T: Parser<I, O, E>,
+{
+    fn map<F, O2>(self, map_fn: F) -> impl Parser<I, O2, E>
+    where
+        F: Fn(O) -> O2,
+    {
+        map(self, map_fn)
+    }
+
+    fn to<O2: Clone>(self, item: O2) -> impl Parser<I, O2, E> {
+        self.map(move |_| item.clone())
+    }
+
+    fn then<O2, P: Parser<I, O2, E>>(self, next: P) -> impl Parser<I, (O, O2), E> {
+        seq2(self, next)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -60,17 +89,20 @@ mod tests {
 
     #[test]
     fn test_map() {
-        let parser = map(
-            seq2(literal("a"), literal("b")),
-            |(_a, _b): (&str, &str)| 59,
-        );
+        let parser =
+            seq2(literal("a"), literal("b")).map(|(a, _b): (&str, &str)| (a.to_uppercase(), 59));
         let output = parser.parse("abcd").unwrap();
-        assert_eq!((59, "cd"), output);
+        assert_eq!((("A".to_owned(), 59), "cd"), output);
+
+        let spaces = repeated(literal_char(' ')).at_least(1);
+        let parser = seq2(literal("lute"), spaces).to(500);
+        assert_eq!(parser.parse("lute    "), Ok((500, "")));
+        assert_eq!(parser.parse("lute"), Err(((), "")));
     }
 
     #[test]
     fn test_combinators() {
-        let parser = seq2(map(repeated(literal_char('a')), |_| 10), literal_char('b'));
+        let parser = repeated(literal_char('a')).to(10).then(literal_char('b'));
         let output = parser.parse("aaaaaaaabcd").unwrap();
         assert_eq! {((10, 'b'), "cd"), output};
     }