Map

src/lib.rs

@@ -1,35 +1,51 @@
 #![feature(assert_matches)]
 #![allow(dead_code)] //TODO eventually turn this off
 
-
 type ParseResult<I, O, E> = Result<(O, I), E>;
 
 trait Parser<I, O, E> {
     fn parse(&self, input: I) -> ParseResult<I, O, E>;
 }
 
-impl<I, O, E, F> Parser<I, O, E> for F where F: Fn(I) -> ParseResult<I, O, E> {
+impl<I, O, E, F> Parser<I, O, E> for F
+where
+    F: Fn(I) -> ParseResult<I, O, E>,
+{
     fn parse(&self, input: I) -> ParseResult<I, O, E> {
         self(input)
     }
 }
 
-fn literal(expected: &'static str) -> impl Fn(&str) -> ParseResult<&str, (), &str> {
+fn literal(expected: &'static str) -> impl Fn(&str) -> ParseResult<&str, &str, &str> {
     move |input| match input.get(0..expected.len()) {
-        Some(next) if next == expected => 
-            Ok(((), &input[expected.len()..])),
-        _  => Err(input)
+        Some(next) if next == expected => Ok((expected, &input[expected.len()..])),
+        _ => Err(input),
     }
 }
 
+fn map<P, F, I, O1, O2, E>(parser: P, map_fn: F) -> impl Parser<I, O2, E>
+where
+    P: Parser<I, O1, E>,
+    F: Fn(O1) -> O2,
+{
+    move |input| parser.parse(input).map(|(result, rest)| (map_fn(result), rest))
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
     use std::assert_matches::assert_matches;
 
     #[test]
-    fn parsing() {
+    fn test_parsing() {
         let output = literal("a")("a yolo");
-        assert_matches!(output.unwrap(), ((), " yolo"));
+        assert_matches!(output.unwrap(), ("a", " yolo"));
+    }
+
+    #[test]
+    fn test_map() {
+        let lit_a = literal("a");
+        let output = map(lit_a, |s| s.to_uppercase()).parse("a yolo");
+        assert_matches!(output.unwrap(), (s, " yolo") if s == "A");
     }
 }