Add function test

dust-lang/src/lexer.rs

@@ -125,6 +125,10 @@ impl<'src> Lexer<'src> {
                         self.position += 2;
 
                         (Token::MinusEqual, Span(self.position - 2, self.position))
+                    } else if let Some('>') = second_char {
+                        self.position += 2;
+
+                        (Token::ArrowThin, Span(self.position - 2, self.position))
                     } else if let Some('0'..='9') = second_char {
                         self.lex_numeric()?
                     } else if "-Infinity" == self.peek_chars(9) {

dust-lang/src/parser.rs

@@ -1111,6 +1111,20 @@ impl<'src> Parser<'src> {
         }
 
         function_parser.advance()?;
+
+        let return_type = if function_parser.allow(Token::ArrowThin)? {
+            let r#type = function_parser.parse_type_from(
+                function_parser.current_token,
+                function_parser.current_position,
+            )?;
+
+            function_parser.advance()?;
+
+            Some(Box::new(r#type))
+        } else {
+            None
+        };
+
         function_parser.expect(Token::LeftCurlyBrace)?;
 
         while function_parser.current_token != Token::RightCurlyBrace {
@@ -1131,7 +1145,6 @@ impl<'src> Parser<'src> {
         self.current_token = function_parser.current_token;
         self.current_position = function_parser.current_position;
 
-        let return_type = take(&mut self.latest_value_type).map(Box::new);
         let function_type = FunctionType {
             type_parameters: None,
             value_parameters,
@@ -1300,6 +1313,11 @@ struct ParseRule<'a> {
 impl From<&Token<'_>> for ParseRule<'_> {
     fn from(token: &Token) -> Self {
         match token {
+            Token::ArrowThin => ParseRule {
+                prefix: Some(Parser::expect_expression),
+                infix: None,
+                precedence: Precedence::None,
+            },
             Token::Async => todo!(),
             Token::Bang => ParseRule {
                 prefix: Some(Parser::parse_unary),

dust-lang/src/token.rs

@@ -38,6 +38,7 @@ pub enum Token<'src> {
     While,
 
     // Symbols
+    ArrowThin,
     BangEqual,
     Bang,
     Colon,
@@ -84,6 +85,7 @@ impl<'src> Token<'src> {
             Token::Integer(text) => text.len(),
             Token::String(text) => text.len() + 2,
             Token::Async => 5,
+            Token::ArrowThin => 2,
             Token::Bool => 4,
             Token::Break => 5,
             Token::Else => 4,
@@ -144,6 +146,7 @@ impl<'src> Token<'src> {
             Token::Integer(text) => text,
             Token::String(text) => text,
             Token::Async => "async",
+            Token::ArrowThin => "->",
             Token::Bool => "bool",
             Token::Break => "break",
             Token::Else => "else",
@@ -195,6 +198,7 @@ impl<'src> Token<'src> {
 
     pub fn to_owned(&self) -> TokenOwned {
         match self {
+            Token::ArrowThin => TokenOwned::ArrowThin,
             Token::Async => TokenOwned::Async,
             Token::BangEqual => TokenOwned::BangEqual,
             Token::Bang => TokenOwned::Bang,
@@ -255,6 +259,7 @@ impl<'src> Token<'src> {
 
     pub fn kind(&self) -> TokenKind {
         match self {
+            Token::ArrowThin => TokenKind::ArrowThin,
             Token::Async => TokenKind::Async,
             Token::BangEqual => TokenKind::BangEqual,
             Token::Bang => TokenKind::Bang,
@@ -359,6 +364,7 @@ impl<'src> Token<'src> {
 impl<'src> Display for Token<'src> {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
         match self {
+            Token::ArrowThin => write!(f, "->"),
             Token::Async => write!(f, "async"),
             Token::BangEqual => write!(f, "!="),
             Token::Bang => write!(f, "!"),
@@ -436,6 +442,7 @@ pub enum TokenOwned {
     String(String),
 
     // Keywords
+    Async,
     Bool,
     Break,
     Else,
@@ -452,7 +459,7 @@ pub enum TokenOwned {
     While,
 
     // Symbols
-    Async,
+    ArrowThin,
     Bang,
     BangEqual,
     Colon,
@@ -490,6 +497,7 @@ pub enum TokenOwned {
 impl Display for TokenOwned {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         match self {
+            TokenOwned::ArrowThin => Token::ArrowThin.fmt(f),
             TokenOwned::Async => Token::Async.fmt(f),
             TokenOwned::Bang => Token::Bang.fmt(f),
             TokenOwned::BangEqual => Token::BangEqual.fmt(f),
@@ -581,6 +589,7 @@ pub enum TokenKind {
     While,
 
     // Symbols
+    ArrowThin,
     BangEqual,
     Bang,
     Colon,
@@ -619,6 +628,7 @@ pub enum TokenKind {
 impl Display for TokenKind {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         match self {
+            TokenKind::ArrowThin => Token::ArrowThin.fmt(f),
             TokenKind::Async => Token::Async.fmt(f),
             TokenKind::Bang => Token::Bang.fmt(f),
             TokenKind::BangEqual => Token::BangEqual.fmt(f),

dust-lang/tests/expressions.rs

@@ -316,6 +316,36 @@ fn equality_assignment_short() {
     assert_eq!(run(source), Ok(Some(Value::boolean(true))));
 }
 
+#[test]
+fn function() {
+    let source = "fn(a: int, b: int) -> int { a + b }";
+
+    assert_eq!(
+        run(source),
+        Ok(Some(Value::function(
+            Chunk::with_data(
+                vec![
+                    (Instruction::add(2, 0, 1), Span(30, 31)),
+                    (Instruction::r#return(true), Span(34, 35)),
+                ],
+                vec![],
+                vec![
+                    Local::new(Identifier::new("a"), Some(Type::Integer), false, 0, 0),
+                    Local::new(Identifier::new("b"), Some(Type::Integer), false, 0, 1)
+                ]
+            ),
+            FunctionType {
+                type_parameters: None,
+                value_parameters: Some(vec![
+                    (Identifier::new("a"), Type::Integer),
+                    (Identifier::new("b"), Type::Integer)
+                ]),
+                return_type: Some(Box::new(Type::Integer)),
+            }
+        )))
+    );
+}
+
 #[test]
 fn greater() {
     let source = "1 > 2";