Add else to if

src/engine.rs

@@ -120,6 +120,7 @@ impl Engine {
                                     let result3 = self.call_fn("clone", Some(a3), None, None, None, None, None);
                                     let result4 = self.call_fn("clone", Some(a4), None, None, None, None, None);
                                     let result5 = self.call_fn("clone", Some(a5), None, None, None, None, None);
+
                                     match (result1, result2, result3, result4, result5) {
                                         (Ok(r1), Ok(r2), Ok(r3), Ok(r4), Ok(r5)) => {
                                             new_scope.push((f.params[0].clone(), r1));
@@ -480,6 +481,20 @@ impl Engine {
                     Err(_) => Err(EvalError::IfGuardMismatch)
                 }
             }
+            Stmt::IfElse(ref guard, ref body, ref else_body) => {
+                let guard_result = try!(self.eval_expr(scope, guard));
+                match guard_result.downcast::<bool>() {
+                    Ok(g) => {
+                        if *g {
+                            self.eval_stmt(scope, body)
+                        }
+                        else {
+                            self.eval_stmt(scope, else_body)
+                        }
+                    }
+                    Err(_) => Err(EvalError::IfGuardMismatch)
+                }
+            }
             Stmt::While(ref guard, ref body) => {
                 loop {
                     let guard_result = try!(self.eval_expr(scope, guard));
@@ -684,6 +699,20 @@ fn test_if() {
     else {
         assert!(false);
     }
+
+    if let Ok(result) = engine.eval("if false { 55 } else { 44 }".to_string()).unwrap().downcast::<i32>() {
+        assert_eq!(*result, 44);
+    }
+    else {
+        assert!(false);
+    }
+
+    if let Ok(result) = engine.eval("if true { 55 } else { 44 }".to_string()).unwrap().downcast::<i32>() {
+        assert_eq!(*result, 55);
+    }
+    else {
+        assert!(false);
+    }
 }
 
 #[test]

src/main.rs

@@ -13,13 +13,13 @@ mod parser;
 
 // Todo (in no particular order):
 // * Doc some examples
-// *   Hello world
-// *   Functions and methods
-// *   Registering types
 // *   Maintaining state
 // *   Overloading
 // *   How it works
 // * Vectors
+// * Return
+// * Break
+// * Tighten parser?
 // * Errors with positions?
 // * Remove empty box values?
 

src/parser.rs

@@ -84,8 +84,8 @@ pub struct FnDef {
 }
 
 #[derive(Debug, Clone)]
-pub enum Stmt { If(Box<Expr>, Box<Stmt>), While(Box<Expr>, Box<Stmt>), Var(String, Option<Box<Expr>>),
+pub enum Stmt { If(Box<Expr>, Box<Stmt>), IfElse(Box<Expr>, Box<Stmt>, Box<Stmt>), While(Box<Expr>, Box<Stmt>), 
-    Block(Box<Vec<Stmt>>), Expr(Box<Expr>) }
+    Var(String, Option<Box<Expr>>), Block(Box<Vec<Stmt>>), Expr(Box<Expr>) }
 
 #[derive(Debug, Clone)]
 pub enum Expr { IntConst(i32), Identifier(String), StringConst(String), FnCall(String, Box<Vec<Expr>>), 
@@ -93,7 +93,7 @@ pub enum Expr { IntConst(i32), Identifier(String), StringConst(String), FnCall(S
 
 #[derive(Debug)]
 pub enum Token { IntConst(i32), Identifier(String), StringConst(String), LCurly, RCurly, LParen, RParen, LSquare, RSquare,
-    Plus, Minus, Multiply, Divide, Semicolon, Colon, Comma, Period, Equals, True, False, Var, If, While,
+    Plus, Minus, Multiply, Divide, Semicolon, Colon, Comma, Period, Equals, True, False, Var, If, Else, While,
     LessThan, GreaterThan, Bang, LessThanEqual, GreaterThanEqual, EqualTo, NotEqualTo, Pipe, Or, Ampersand, And, Fn,
     LexErr(LexError) }
 
@@ -151,6 +151,9 @@ impl<'a> Iterator for TokenIterator<'a> {
                     else if out == "if" {
                         return Some(Token::If);
                     }
+                    else if out == "else" {
+                        return Some(Token::Else);
+                    }
                     else if out == "while" {
                         return Some(Token::While);
                     }
@@ -482,7 +485,16 @@ fn parse_if<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, ParseEr
     let guard = try!(parse_expr(input));
     let body = try!(parse_block(input));
 
-    Ok(Stmt::If(Box::new(guard), Box::new(body)))
+    match input.peek() {
+        Some(& Token::Else) => {
+            input.next();
+            let else_body = try!(parse_block(input));
+            Ok(Stmt::IfElse(Box::new(guard), Box::new(body), Box::new(else_body)))
+        }
+        _ => {
+            Ok(Stmt::If(Box::new(guard), Box::new(body)))
+        }
+    }
 }
 
 fn parse_while<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, ParseError> {