Commit

src/lib.rs

@@ -1,14 +1,35 @@
-pub fn add(left: usize, right: usize) -> usize {
-    left + right
+#![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> {
+    fn parse(&self, input: I) -> ParseResult<I, O, E> {
+        self(input)
+    }
+}
+
+fn literal(expected: &'static str) -> impl Fn(&str) -> ParseResult<&str, (), &str> {
+    move |input| match input.get(0..expected.len()) {
+        Some(next) if next == expected => 
+            Ok(((), &input[expected.len()..])),
+        _  => Err(input)
+    }
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
+    use std::assert_matches::assert_matches;
 
     #[test]
-    fn it_works() {
-        let result = add(2, 2);
-        assert_eq!(result, 4);
+    fn parsing() {
+        let output = literal("a")("a yolo");
+        assert_matches!(output.unwrap(), ((), " yolo"));
     }
 }