Added If/Else Evaluator

1. Added If Else evaluator
2. Added tests to support expression evaluator
3. Fixed issues reported by clippy

src/evaluator/mod.rs

@@ -29,7 +29,7 @@ impl Object {
 #[cfg(test)]
 mod tests {
     use crate::{
-        evaluator::{tree_walker::TreeWalker, Evaluator, Object},
+        evaluator::{tree_walker::TreeWalker, Evaluator, Object, FALSE, NULL, TRUE},
         lexer::Lexer,
         parser::{ast::Node, Parser},
     };
@@ -56,16 +56,16 @@ mod tests {
     #[test]
     fn eval_boolean_expression() {
         let test_cases = [
-            ("true", Some(Object::Boolean(true))),
+            ("true", Some(TRUE)),
-            ("false", Some(Object::Boolean(false))),
+            ("false", Some(FALSE)),
-            ("3 < 4", Some(Object::Boolean(true))),
+            ("3 < 4", Some(TRUE)),
-            ("3 > 4", Some(Object::Boolean(false))),
+            ("3 > 4", Some(FALSE)),
-            ("3 == 4", Some(Object::Boolean(false))),
+            ("3 == 4", Some(FALSE)),
-            ("3 != 4", Some(Object::Boolean(true))),
+            ("3 != 4", Some(TRUE)),
-            ("(1 < 2 ) == true", Some(Object::Boolean(true))),
+            ("(1 < 2 ) == true", Some(TRUE)),
-            ("(1 < 2 ) == false", Some(Object::Boolean(false))),
+            ("(1 < 2 ) == false", Some(FALSE)),
-            ("(1 > 2 ) == true", Some(Object::Boolean(false))),
+            ("(1 > 2 ) == true", Some(FALSE)),
-            ("(1 > 2 ) == false", Some(Object::Boolean(true))),
+            ("(1 > 2 ) == false", Some(TRUE)),
         ];
 
         for test in test_cases.iter() {
@@ -83,12 +83,12 @@ mod tests {
     #[test]
     fn eval_bang_operator() {
         let test_cases = [
-            ("!5", Some(Object::Boolean(false))),
+            ("!5", Some(FALSE)),
-            ("!!true", Some(Object::Boolean(true))),
+            ("!!true", Some(TRUE)),
-            ("!!false", Some(Object::Boolean(false))),
+            ("!!false", Some(FALSE)),
-            ("!!5", Some(Object::Boolean(true))),
+            ("!!5", Some(TRUE)),
-            ("!true", Some(Object::Boolean(false))),
+            ("!true", Some(FALSE)),
-            ("!false", Some(Object::Boolean(true))),
+            ("!false", Some(TRUE)),
         ];
         for test in test_cases.iter() {
             let lexer = Lexer::new(test.0);
@@ -132,4 +132,37 @@ mod tests {
             assert_eq!(eval, test.1);
         }
     }
+
+    #[test]
+    fn eval_if_else_expression() {
+        let test_cases = [
+            // (
+            //     "if (x > 10) {
+            //         puts(\"everything okay\");
+            //     } else {
+            //         puts(\"x is too low!\");
+            //         potato();
+            //     }",
+            //     Object::Null,
+            // ),
+            ("if(true) {10}", Some(Object::Integer(10))),
+            ("if(false) {10}", Some(NULL)),
+            ("if (1) {10}", Some(Object::Integer(10))),
+            ("if(1 < 2) {10}", Some(Object::Integer(10))),
+            ("if (1 > 2) {10}", Some(NULL)),
+            ("if(1 > 2) {10} else {20}", Some(Object::Integer(20))),
+            ("if (1 < 2) {10} else {20}", Some(Object::Integer(10))),
+        ];
+
+        for test in test_cases.iter() {
+            let lexer = Lexer::new(test.0);
+            let mut parser = Parser::new(lexer);
+            let program = parser.parse_program();
+            assert!(program.is_some());
+            let program = program.unwrap();
+            let evaluator = TreeWalker::new();
+            let eval = evaluator.eval(Node::Program(program));
+            assert_eq!(eval, test.1);
+        }
+    }
 }

src/evaluator/tree_walker/mod.rs

@@ -20,6 +20,7 @@ impl Evaluator for TreeWalker {
                 Statement::ExpressionStatement(ExpressionStatement { expression, .. }) => {
                     self.eval(Node::Expression(expression))
                 }
+                Statement::BlockStatement(bs) => self.eval_statements(bs.statements),
                 _ => None,
             },
             Node::Expression(expr) => match expr {
@@ -32,9 +33,19 @@ impl Evaluator for TreeWalker {
                 Expression::InfixExpression(ie) => {
                     let left = self.eval(Node::Expression(*ie.left))?;
                     let right = self.eval(Node::Expression(*ie.right))?;
-
                     self.eval_infix_expression(left, ie.operator, right)
                 }
+                Expression::IfExpression(ie) => {
+                    let condition = self.eval(Node::Expression(*ie.condition))?;
+
+                    if self.is_truthy(&condition) {
+                        self.eval(Node::Statement(Statement::BlockStatement(ie.consequence)))
+                    } else if let Some(alternative) = ie.alternative {
+                        self.eval(Node::Statement(Statement::BlockStatement(alternative)))
+                    } else {
+                        Some(NULL)
+                    }
+                }
                 _ => None,
             },
         }
@@ -99,4 +110,13 @@ impl TreeWalker {
             _ => NULL,
         }
     }
+
+    fn is_truthy(&self, obj: &Object) -> bool {
+        match *obj {
+            NULL => false,
+            TRUE => true,
+            FALSE => false,
+            _ => true,
+        }
+    }
 }

src/parser/ast/mod.rs

@@ -413,9 +413,9 @@ impl Display for BooleanExpression {
 
 #[derive(Debug, PartialEq)]
 pub struct IfExpression {
-    condition: Box<Expression>,
+    pub condition: Box<Expression>,
-    consequence: BlockStatement,
+    pub consequence: BlockStatement,
-    alternative: Option<BlockStatement>,
+    pub alternative: Option<BlockStatement>,
 }
 
 impl IfExpression {
@@ -465,7 +465,7 @@ impl Display for IfExpression {
 
 #[derive(Debug, PartialEq)]
 pub struct BlockStatement {
-    statements: Vec<Statement>,
+    pub statements: Vec<Statement>,
 }
 
 impl BlockStatement {

src/parser/mod.rs

@@ -171,9 +171,7 @@ mod tests {
     };
 
     fn check_parser_errors(p: &Parser) {
-        if p.errors.is_empty() {
+        if !p.errors.is_empty() {
-            return;
-        } else {
             let mut out = String::new();
             out.push_str(&format!("parser has {} errors\n", p.errors.len()));
             for error in &p.errors {