From 0ee53b8f00786a01cc6bc873f05cf7ba24a7d1ad Mon Sep 17 00:00:00 2001
From: Greg Shuflin <greg.shuflin@protonmail.com>
Date: Sat, 15 Oct 2022 23:58:05 -0700
Subject: [PATCH] Sequence

---
 src/lib.rs | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 53 insertions(+), 1 deletion(-)

diff --git a/src/lib.rs b/src/lib.rs
index 2807dc3..7ac320b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -28,7 +28,47 @@ where
     P: Parser<I, O1, E>,
     F: Fn(O1) -> O2,
 {
-    move |input| parser.parse(input).map(|(result, rest)| (map_fn(result), rest))
+    move |input| {
+        parser
+            .parse(input)
+            .map(|(result, rest)| (map_fn(result), rest))
+    }
+}
+
+fn seq<P1, P2, I, O1, O2, E>(parser1: P1, parser2: P2) -> impl Parser<I, (O1, O2), E>
+where
+    P1: Parser<I, O1, E>,
+    P2: Parser<I, O2, E>,
+{
+    move |input| {
+        parser1.parse(input).and_then(|(result1, rest1)| {
+            parser2
+                .parse(rest1)
+                .map(|(result2, rest2)| ((result1, result2), rest2))
+        })
+    }
+}
+
+/// Parses a standard identifier in a programming language
+fn identifier(input: &str) -> ParseResult<&str, String, &str> {
+    let mut chars = input.chars();
+    let mut buf = String::new();
+
+    match chars.next() {
+        Some(ch) if ch.is_alphabetic() => buf.push(ch),
+        _ => return Err(input),
+    }
+
+    while let Some(next) = chars.next() {
+        if next.is_alphanumeric() {
+            buf.push(next);
+        } else {
+            break;
+        }
+    }
+
+    let next_index = buf.len();
+    Ok((buf, &input[next_index..]))
 }
 
 #[cfg(test)]
@@ -42,10 +82,22 @@ mod tests {
         assert_matches!(output.unwrap(), ("a", " yolo"));
     }
 
+    #[test]
+    fn test_identifier() {
+        assert_matches!(identifier("bongo1beans"), Ok((s, "")) if s == "bongo1beans");
+        assert_matches!(identifier("2bongo1beans"), Err("2bongo1beans"));
+    }
+
     #[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");
     }
+
+    #[test]
+    fn test_seq() {
+        let p = seq(identifier, seq(literal(" "), literal("ruts")));
+        assert_matches!(p.parse("fort1 ruts"), Ok((r, "")) if r.0 == "fort1" && r.1 == (" ", "ruts") );
+    }
 }