From ee3db87e63a7c1d1dca9ee5eb1bb9525dea86f49 Mon Sep 17 00:00:00 2001
From: Arnaud Bailly <arnaud.bailly@iohk.io>
Date: Tue, 24 Sep 2024 11:28:47 +0200
Subject: Parse binary application with parens

---
 rust/src/parser.rs | 30 ++++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

(limited to 'rust/src/parser.rs')

diff --git a/rust/src/parser.rs b/rust/src/parser.rs
index 50cf918..8f95ca9 100644
--- a/rust/src/parser.rs
+++ b/rust/src/parser.rs
@@ -8,8 +8,27 @@ enum Token {
 }
 
 pub fn parse(arg: &str) -> Value {
-    let tokens = tokenize(arg);
-    parse_value(&tokens[0]).unwrap()
+    let mut tokens = tokenize(arg);
+    let mut state = Vec::new();
+    parse_tokens(&mut tokens, &mut state).unwrap()
+}
+
+fn parse_tokens(tokens: &mut [Token], state: &mut Vec<Value>) -> Result<Value, String> {
+    match tokens {
+        [] => state.pop().ok_or("Empty expression".to_string()),
+        [Token::LParen, rest @ ..] => parse_tokens(rest, state),
+        [Token::RParen, rest @ ..] => {
+            let right = state.pop().ok_or("Unbalanced parentheses".to_string())?;
+            let left = state.pop().ok_or("Unbalanced parentheses".to_string())?;
+            state.push(Value::App(Box::new(left), Box::new(right)));
+            parse_tokens(rest, state)
+        }
+        [Token::Word(s), rest @ ..] => {
+            let value = parse_value(&Token::Word(s.clone()))?;
+            state.push(value);
+            parse_tokens(rest, state)
+        }
+    }
 }
 
 fn parse_value(token: &Token) -> Result<Value, String> {
@@ -133,6 +152,13 @@ mod tests {
             tokenize("(   \r() 42)  \ntrue(  ")
         );
     }
+
+    #[test]
+    fn parse_application_of_two_values() {
+        assert_eq!(
+            App(Box::new(Sym("foo".to_string())), Box::new(Num(42))),
+            parse("(foo 42)")
+        );
     }
 
     impl Arbitrary for Value {
-- 
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