From 0321e9ba89a29886df1f72b3f4a727b4aae80bfe Mon Sep 17 00:00:00 2001
From: Devon Tingley <dtingley@twilit.io>
Date: Mon, 6 Mar 2023 18:05:40 -0500
Subject: [PATCH] Chapter 2 (finished)

---
 src/lexer/tokens.rs      |  4 ++++
 src/parser/ast.rs        | 17 ++++++++++++++-
 src/parser/mod.rs        | 47 ++++++++++++++++++++++++++++++++++++++++
 src/parser/precedence.rs |  4 +++-
 4 files changed, 70 insertions(+), 2 deletions(-)

diff --git a/src/lexer/tokens.rs b/src/lexer/tokens.rs
index ce6dc34..598c64d 100644
--- a/src/lexer/tokens.rs
+++ b/src/lexer/tokens.rs
@@ -132,6 +132,8 @@ pub enum InfixOperator {
     GreaterThan,
     LessThanEqual,
     GreaterThanEqual,
+
+    Call,
 }
 
 impl InfixOperator {
@@ -157,6 +159,8 @@ impl TryFrom<&Token> for InfixOperator {
             Token::GreaterThan => Self::GreaterThan,
             Token::GreaterThanEqual => Self::GreaterThanEqual,
 
+            Token::LeftParenthesis => Self::Call,
+
             _ => return Err(LexerError::InvalidToken),
         };
 
diff --git a/src/parser/ast.rs b/src/parser/ast.rs
index 6cfc6c0..b92e82b 100644
--- a/src/parser/ast.rs
+++ b/src/parser/ast.rs
@@ -85,7 +85,12 @@ pub enum Expression {
 
     Function {
         parameters: Vec<String>,
-        body: Box<Node>,
+        body: Box<Node>, // block statement
+    },
+
+    Call {
+        function: Box<Expression>, // ident or function
+        args: Vec<Expression>,
     },
 }
 
@@ -159,6 +164,16 @@ impl Display for Expression {
             Expression::Function { parameters, body } => {
                 write!(f, "fn({}) {}", parameters.join(", "), body)
             }
+
+            Expression::Call { function, args } => write!(
+                f,
+                "{}({})",
+                function,
+                args.iter()
+                    .map(|expr| expr.to_string())
+                    .collect::<Vec<String>>()
+                    .join(", ")
+            ),
         }
     }
 }
diff --git a/src/parser/mod.rs b/src/parser/mod.rs
index 5fcea26..8e94fd1 100644
--- a/src/parser/mod.rs
+++ b/src/parser/mod.rs
@@ -161,6 +161,7 @@ fn parse_expression(
             None
             | Some(Token::RightParenthesis)
             | Some(Token::Semicolon)
+            | Some(Token::Comma) // Break used when parsing function arguments
             | Some(Token::LeftBrace) // Break used for if statements
             | Some(Token::RightBrace) => break,
             _ => (),
@@ -315,6 +316,39 @@ fn parse_infix_operator(
     lhs: Expression,
 ) -> Result<Expression, ParserError> {
     let lhs = Box::new(lhs);
+
+    // Call operators are parsed weirdly
+    if InfixOperator::Call == operator {
+        let mut args = Vec::new();
+        loop {
+            match tokens.peek() {
+                Some(Token::Comma) => {
+                    tokens.next();
+                    continue;
+                }
+                Some(Token::RightParenthesis) => {
+                    tokens.next();
+                    break;
+                }
+
+                // Parse expressions
+                Some(_) => {
+                    let arg = parse_expression(tokens, Precedence::Lowest)?;
+                    args.push(arg);
+                    continue;
+                }
+
+                // Unexpected EOF
+                None => return Err(ParserError::EOF),
+            };
+        }
+
+        return Ok(Expression::Call {
+            function: lhs,
+            args,
+        });
+    };
+
     let rhs = Box::new(parse_expression(tokens, get_prescedence(&operator))?);
 
     let expr = match operator {
@@ -331,6 +365,8 @@ fn parse_infix_operator(
         InfixOperator::LessThan => Expression::LessThan(lhs, rhs),
         InfixOperator::GreaterThanEqual => Expression::GreaterThanEqual(lhs, rhs),
         InfixOperator::LessThanEqual => Expression::LessThanEqual(lhs, rhs),
+
+        InfixOperator::Call => panic!("unreachable"),
     };
 
     Ok(expr)
@@ -424,4 +460,15 @@ mod tests {
         let res = parse_expression(&mut tokens, Precedence::Lowest).unwrap();
         assert_eq!(&res.to_string(), expected);
     }
+
+    #[rstest]
+    #[case("add(2, 3)", "add(2, 3)")]
+    #[case("add(1 + 2, 3)", "add((1 + 2), 3)")]
+    #[case("add(x, y)", "add(x, y)")]
+    #[case("fn(x,y) { x + y }(1,2)", "fn(x, y) { (x + y) }(1, 2)")]
+    fn test_call_expression(#[case] input: &str, #[case] expected: &str) {
+        let mut tokens = lexer::tokenize(input).unwrap();
+        let res = parse_expression(&mut tokens, Precedence::Lowest).unwrap();
+        assert_eq!(&res.to_string(), expected);
+    }
 }
diff --git a/src/parser/precedence.rs b/src/parser/precedence.rs
index 202e872..c313c44 100644
--- a/src/parser/precedence.rs
+++ b/src/parser/precedence.rs
@@ -8,7 +8,7 @@ pub enum Precedence {
     Sum,
     Product,
     Prefix,
-    // Call,
+    Call,
 }
 
 pub(super) fn get_prescedence(tok: &InfixOperator) -> Precedence {
@@ -26,5 +26,7 @@ pub(super) fn get_prescedence(tok: &InfixOperator) -> Precedence {
 
         InfixOperator::Asterisk => Precedence::Product,
         InfixOperator::ForwardSlash => Precedence::Product,
+
+        InfixOperator::Call => Precedence::Call,
     }
 }