zero or more

src/lib.rs

@@ -1,5 +1,6 @@
 #![feature(assert_matches)]
 #![allow(dead_code)] //TODO eventually turn this off
+use std::rc::Rc;
 
 type ParseResult<I, O, E> = Result<(O, I), E>;
 
@@ -16,6 +17,15 @@ where
     }
 }
 
+impl<I, O, E, T> Parser<I, O, E> for Rc<T>
+where
+    T: Parser<I, O, E>,
+{
+    fn parse(&self, input: I) -> ParseResult<I, O, E> {
+        self.as_ref().parse(input)
+    }
+}
+
 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((expected, &input[expected.len()..])),
@@ -49,7 +59,7 @@ where
     }
 }
 
-fn one_or_more<P, I, O>(parser: P) -> impl Parser<I, Vec<O>, I>
+fn zero_or_more<P, I, O>(parser: P) -> impl Parser<I, Vec<O>, I>
 where
     P: Parser<I, O, I>,
     I: Copy,
@@ -57,13 +67,6 @@ where
     move |mut input| {
         let mut results = Vec::new();
 
-        if let Ok((result, rest)) = parser.parse(input) {
-            results.push(result);
-            input = rest;
-        } else {
-            return Err(input);
-        }
-
         while let Ok((item, rest)) = parser.parse(input) {
             results.push(item);
             input = rest;
@@ -73,6 +76,22 @@ where
     }
 }
 
+fn one_or_more<P, I, O>(parser: P) -> impl Parser<I, Vec<O>, I>
+where
+    P: Parser<I, O, I>,
+    I: Copy,
+{
+    let parser = std::rc::Rc::new(parser);
+    map(
+        seq(parser.clone(), zero_or_more(parser)),
+        |(first, rest)| {
+            let mut output = vec![first];
+            output.extend(rest.into_iter());
+            output
+        },
+    )
+}
+
 /// Parses a standard identifier in a programming language
 fn identifier(input: &str) -> ParseResult<&str, String, &str> {
     let mut chars = input.chars();
@@ -130,5 +149,7 @@ mod tests {
         let p = one_or_more(literal("bongo "));
         let input = "bongo bongo bongo bongo bongo ";
         assert_matches!(p.parse(input), Ok((v, "")) if v.len() == 5);
+        let input = "bongo ecks";
+        assert_matches!(p.parse(input), Ok((v, "ecks")) if v.len() == 1);
     }
 }