Rewrite

src/lib.rs

@@ -1,35 +1,77 @@
-#![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((next, &input[expected.len()..])),
+        _ => Err(input),
+    }
+}
+
+fn sequence<I, O1, O2, E>(
+    first: impl Parser<I, O1, E>,
+    second: impl Parser<I, O2, E>,
+) -> impl Parser<I, (O1, O2), E> {
+    move |input| -> ParseResult<I, (O1, O2), E> {
+        first.parse(input).and_then(|(result1, rest)| {
+            second
+                .parse(rest)
+                .map(|(result2, rest2)| ((result1, result2), rest2))
+        })
+    }
+}
+
+fn choice<'a, I, O, E>(parsers: &'a [&'a dyn Parser<I, O, E>]) -> impl Parser<I, O, E> + 'a
+where
+    I: Clone,
+{
+    move |input: I| {
+        //TODO need a more principled way to return an error when no choices work
+        let mut err = None;
+
+        for parser in parsers.iter() {
+            match parser.parse(input.clone()) {
+                Ok(res) => return Ok(res),
+                Err(e) => {
+                    err = Some(e);
+                }
+            }
+        }
+        Err(err.unwrap())
     }
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
-    use std::assert_matches::assert_matches;
 
     #[test]
     fn parsing() {
-        let output = literal("a")("a yolo");
-        assert_matches!(output.unwrap(), ((), " yolo"));
+        let (parsed, rest) = literal("a")("a yolo").unwrap();
+        assert_eq!(parsed, "a");
+        assert_eq!(rest, " yolo");
+    }
+
+    #[test]
+    fn test_sequence() {
+        let parser = sequence(literal("bongo"), sequence(literal(" "), literal("jonzzz")));
+        let output = parser.parse("bongo jonzzz").unwrap();
+        assert_eq!(output.0 .0, "bongo");
+        assert_eq!(output.0 .1, (" ", "jonzzz"));
+        assert_eq!(output.1, "");
     }
 }