if

src/lexer.rs

@@ -47,6 +47,8 @@ pub enum Token {
     Comma,
     Eol,
 
+    If,
+    Else,
     Return,
 
     Not,
@@ -68,6 +70,7 @@ pub enum Token {
 pub enum Precedence {
     Min,
     Return,
+    If,
     Assign,
     Logical,
     Equality,
@@ -86,6 +89,7 @@ impl Token {
     pub fn prefix_precedence(&self) -> Option<Precedence> {
         Some(match self {
             Token::Return => Precedence::Return,
+            Token::If => Precedence::If,
             Token::Minus | Token::Not => Precedence::NegateNot,
             _ => return None,
         })
@@ -192,6 +196,8 @@ where
 
         match word.as_str() {
             "return" => Token::Return,
+            "if" => Token::If,
+            "else" => Token::Else,
             "true" => Token::Literal(Literal::Boolean(true)),
             "false" => Token::Literal(Literal::Boolean(false)),
             "nil" => Token::Literal(Literal::Nil),

src/parser.rs

@@ -12,6 +12,7 @@ pub enum Expr {
     // Runtime datatypes
     Block(Block),
     // Control flow
+    If(Box<Expr>, Box<Expr>, Option<Box<Expr>>),
     Return(Box<Expr>),
     Call(Box<Expr>, Vec<Expr>),
     // Unary operations
@@ -137,6 +138,19 @@ where
                     Token::Minus => Expr::Negate(rhs),
                     Token::Not => Expr::Not(rhs),
                     Token::Return => Expr::Return(rhs),
+                    Token::If => {
+                        // parse the true case
+                        let true_case = self.parse_expr(Precedence::Min, false)?;
+                        // and maybe a false case
+                        let false_case = matches!(self.try_peek(), Ok(Token::Else))
+                            .then(|| {
+                                self.eat();
+                                self.parse_expr(Precedence::Min, false)
+                            })
+                            .transpose()?;
+                        // pack
+                        Expr::If(rhs, true_case, false_case)
+                    }
                     _ => unreachable!(),
                 })
             }
@@ -238,15 +252,14 @@ where
             match self.try_peek() {
                 // end (block)
                 Ok(Token::CurlyClose) if in_block => break,
-                // end (stream) lpwkey idk if this is a good way to check for error
-                // need to add error nodes anyway so whatever
+                // end (stream)
                 Err(ParseError::UnexpectedEnd) if !in_block => break,
 
                 // try to parse expr
                 Ok(_) => exprs.push(*self.parse_expr(Precedence::Min, false)?),
 
                 // invalid
-                Err(err) => return Err(err),
+                Err(_) => unreachable!(),
             }
         }
         Ok(Block { exprs })

src/parser/util.rs

@@ -31,6 +31,13 @@ fn fmt_expr(e: Expr, depth: usize) -> String {
             result.push(')');
             result
         }
+        Expr::If(c, t, f) => {
+            let mut result = format!("if ({}) ({})", fmt_expr(*c, depth), fmt_expr(*t, depth));
+            if let Some(f) = f {
+                result.push_str(&format!(" else ({})", fmt_expr(*f, depth)));
+            }
+            result
+        }
         Expr::Return(l) => format!("return {}", fmt_expr(*l, depth)),
         Expr::Block(b) => {
             let mut result = String::new();