Added If and IfElse parser

1. Added If and IfElse expression parsers.
2. Also, Added asserts to ensure there are 0 errors in parser object

src/parser/ast/mod.rs

@@ -32,6 +32,7 @@ pub enum Statement {
     Let(LetStatement),
     Return(ReturnStatement),
     ExpressionStatement(ExpressionStatement),
+    BlockStatement(BlockStatement),
 }
 
 impl<'a> Statement {
@@ -46,12 +47,13 @@ impl<'a> Statement {
     }
 }
 
-impl Display for Statement {
+impl ToString for Statement {
-    fn fmt(&self, f: &mut Formatter) -> Result<(), FmtError> {
+    fn to_string(&self) -> String {
         match self {
-            Statement::Let(v) => write!(f, "{}", v.to_string()),
+            Statement::Let(v) => v.to_string(),
-            Statement::Return(v) => write!(f, "{}", v.to_string()),
+            Statement::Return(v) => v.to_string(),
-            Statement::ExpressionStatement(v) => write!(f, "{}", v.to_string()),
+            Statement::ExpressionStatement(v) => v.to_string(),
+            Statement::BlockStatement(v) => v.to_string(),
         }
     }
 }
@@ -160,9 +162,9 @@ impl ExpressionStatement {
     }
 }
 
-impl Display for ExpressionStatement {
+impl ToString for ExpressionStatement {
-    fn fmt(&self, f: &mut Formatter) -> Result<(), FmtError> {
+    fn to_string(&self) -> String {
-        write!(f, "{}", self.expression.to_string())
+        String::from(self.expression.to_string())
     }
 }
 
@@ -184,6 +186,7 @@ pub enum Expression {
     PrefixExpression(PrefixExpression),
     InfixExpression(InfixExpression),
     BooleanExpression(BooleanExpression),
+    IfExpression(IfExpression),
     // TODO: Temporary placeholder value. Should be removed once this section is done
     None,
 }
@@ -241,6 +244,58 @@ impl Expression {
         Some(Self::BooleanExpression(BooleanExpression::new(token.name)))
     }
 
+    pub fn parse_grouped_expression(parser: &mut Parser, _token: Token) -> Option<Self> {
+        let next_token = parser.lexer.next()?;
+        let expr = Expression::parse(parser, next_token, ExpressionPriority::Lowest);
+
+        if parser.expect_peek(TokenType::RParen).is_none() {
+            None
+        } else {
+            expr
+        }
+    }
+
+    pub fn parse_if_expression(parser: &mut Parser, ctoken: Token) -> Option<Self> {
+        if parser.expect_peek(TokenType::LParen).is_none() {
+            return None;
+        }
+        let next_token = parser.lexer.next()?;
+        let condition = Expression::parse(parser, next_token.clone(), ExpressionPriority::Lowest)?;
+
+        if parser.expect_peek(TokenType::RParen).is_none() {
+            return None;
+        }
+        if parser.expect_peek(TokenType::LBrace).is_none() {
+            return None;
+        }
+
+        let consequence = BlockStatement::parse(parser, next_token)?;
+
+        if parser.peek_token_is(TokenType::Else) {
+            let token = parser.lexer.next()?;
+
+            if parser.expect_peek(TokenType::LBrace).is_none() {
+                return None;
+            }
+
+            let alternative = BlockStatement::parse(parser, token);
+
+            Some(Expression::IfExpression(IfExpression::new(
+                ctoken.name,
+                condition,
+                consequence,
+                alternative,
+            )))
+        } else {
+            Some(Expression::IfExpression(IfExpression::new(
+                ctoken.name,
+                condition,
+                consequence,
+                None,
+            )))
+        }
+    }
+
     pub fn parse_prefix_expression(parser: &mut Parser, ctoken: Token) -> Option<Self> {
         let next_token = parser.lexer.next()?;
         let right_expr = Expression::parse(parser, next_token.clone(), ExpressionPriority::Prefix)?;
@@ -279,6 +334,7 @@ impl Display for Expression {
                 Expression::PrefixExpression(v) => v.to_string(),
                 Expression::InfixExpression(v) => v.to_string(),
                 Expression::BooleanExpression(v) => v.to_string(),
+                Expression::IfExpression(v) => v.to_string(),
                 Expression::None => "None".into(),
             }
         )
@@ -405,6 +461,90 @@ impl Display for BooleanExpression {
     }
 }
 
+#[derive(Debug, PartialEq)]
+pub struct IfExpression {
+    token: TokenType,
+    condition: Box<Expression>,
+    consequence: BlockStatement,
+    alternative: Option<BlockStatement>,
+}
+
+impl IfExpression {
+    pub fn new(
+        token: TokenType,
+        condition: Expression,
+        consequence: BlockStatement,
+        alternative: Option<BlockStatement>,
+    ) -> Self {
+        Self {
+            token,
+            condition: Box::new(condition),
+            consequence,
+            alternative,
+        }
+    }
+}
+
+impl ToString for IfExpression {
+    fn to_string(&self) -> String {
+        let mut out = format!(
+            "if {} {{ {} }} ",
+            self.condition.to_string(),
+            self.consequence.to_string()
+        );
+        if let Some(alternative) = &self.alternative {
+            out += &format!("else {{ {} }}", alternative.to_string());
+        }
+        out
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub struct BlockStatement {
+    token: Token,
+    statements: Vec<Statement>,
+}
+
+impl BlockStatement {
+    pub fn new(token: Token, stmt: Vec<Statement>) -> Self {
+        Self {
+            token,
+            statements: stmt,
+        }
+    }
+
+    pub fn parse(parser: &mut Parser, ogtoken: Token) -> Option<Self> {
+        let mut stmts = vec![];
+
+        let mut ctoken = parser.lexer.next();
+
+        while let Some(token) = ctoken {
+            if token.name == TokenType::RBrace {
+                break;
+            }
+
+            let stmt = Statement::parse(parser, token);
+            if stmt.is_some() {
+                stmts.push(stmt.unwrap());
+            }
+            ctoken = parser.lexer.next();
+        }
+
+        Some(BlockStatement::new(ogtoken, stmts))
+    }
+}
+
+impl ToString for BlockStatement {
+    fn to_string(&self) -> String {
+        let mut out = String::new();
+
+        for stmt in &self.statements {
+            out.push_str(&stmt.to_string());
+        }
+        out
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::{

src/parser/mod.rs

@@ -53,6 +53,8 @@ impl<'a> Parser<'a> {
         parser.register_prefix(TokenType::Minus, Expression::parse_prefix_expression);
         parser.register_prefix(TokenType::True, Expression::parse_boolean);
         parser.register_prefix(TokenType::False, Expression::parse_boolean);
+        parser.register_prefix(TokenType::LParen, Expression::parse_grouped_expression);
+        parser.register_prefix(TokenType::If, Expression::parse_if_expression);
 
         parser.register_infix(TokenType::Plus, Expression::parse_infix_expression);
         parser.register_infix(TokenType::Minus, Expression::parse_infix_expression);
@@ -182,6 +184,7 @@ mod tests {
         let mut parser = Parser::new(lexer);
         let program = parser.parse_program();
         check_parser_errors(&parser);
+        assert_eq!(parser.errors.len(), 0);
         assert!(program.is_some());
         let program = program.unwrap();
         assert_eq!(program.statements.len(), 3);
@@ -219,6 +222,7 @@ mod tests {
         let program = parser.parse_program();
 
         check_parser_errors(&parser);
+        assert_eq!(parser.errors.len(), 0);
         assert!(program.is_some());
         let program = program.unwrap();
         assert_eq!(program.statements.len(), 3);
@@ -232,6 +236,7 @@ mod tests {
         let program = parser.parse_program();
 
         check_parser_errors(&parser);
+        assert_eq!(parser.errors.len(), 0);
         assert!(program.is_some());
         let program = program.unwrap();
         assert_eq!(program.statements.len(), 1);
@@ -250,6 +255,7 @@ mod tests {
         let mut parser = Parser::new(lexer);
         let program = parser.parse_program();
         check_parser_errors(&parser);
+        assert_eq!(parser.errors.len(), 0);
         assert!(program.is_some());
 
         assert_eq!(
@@ -340,6 +346,7 @@ mod tests {
             let mut parser = Parser::new(lexer);
             let program = parser.parse_program();
             check_parser_errors(&parser);
+            assert_eq!(parser.errors.len(), 0);
             assert!(program.is_some());
             assert_eq!(program.unwrap().statements, test.1);
         }
@@ -467,6 +474,7 @@ mod tests {
             let mut parser = Parser::new(lexer);
             let program = parser.parse_program();
             check_parser_errors(&parser);
+            assert_eq!(parser.errors.len(), 0);
             assert!(program.is_some());
             assert_eq!(program.unwrap().statements, test.1);
         }
@@ -498,6 +506,11 @@ mod tests {
             ("false", "false"),
             ("3 > 5 == false", "((3 > 5) == false)"),
             ("3 < 5 == true", "((3 < 5) == true)"),
+            ("1 + (2 + 3) + 4", "((1 + (2 + 3)) + 4)"),
+            ("(5 + 5) * 2", "((5 + 5) * 2)"),
+            ("2 / (5 + 5)", "(2 / (5 + 5))"),
+            ("-(5 + 5)", "(-(5 + 5))"),
+            ("!(true == true)", "(!(true == true))"),
         ];
 
         for test in test_cases.iter() {
@@ -505,6 +518,7 @@ mod tests {
             let mut parser = Parser::new(lexer);
             let program = parser.parse_program();
             check_parser_errors(&parser);
+            assert_eq!(parser.errors.len(), 0);
             assert!(program.is_some());
             assert_eq!(program.unwrap().to_string(), test.1);
         }
@@ -547,6 +561,98 @@ mod tests {
             let mut parser = Parser::new(lexer);
             let program = parser.parse_program();
             check_parser_errors(&parser);
+            assert_eq!(parser.errors.len(), 0);
+            assert!(program.is_some());
+            assert_eq!(program.unwrap(), test.1);
+        }
+    }
+    #[test]
+    fn if_expression() {
+        let test_cases = [(
+            "if (x > y) { x };",
+            Program {
+                statements: vec![Statement::ExpressionStatement(ExpressionStatement::new(
+                    Token::new(TokenType::If),
+                    Expression::IfExpression(IfExpression::new(
+                        TokenType::If,
+                        Expression::InfixExpression(InfixExpression::new(
+                            Token::new(TokenType::GreaterThan),
+                            Expression::Identifier(Identifier::new(TokenType::Ident, "x")),
+                            ">",
+                            Expression::Identifier(Identifier::new(TokenType::Ident, "y")),
+                        )),
+                        BlockStatement::new(
+                            Token::with_value(TokenType::Ident, "x"),
+                            vec![Statement::ExpressionStatement(ExpressionStatement {
+                                token: Token::with_value(TokenType::Ident, "x"),
+                                expression: Expression::Identifier(Identifier::new(
+                                    TokenType::Ident,
+                                    "x",
+                                )),
+                            })],
+                        ),
+                        None,
+                    )),
+                ))],
+            },
+        )];
+
+        for test in test_cases.iter() {
+            let lexer = Lexer::new(test.0);
+            let mut parser = Parser::new(lexer);
+            let program = parser.parse_program();
+            check_parser_errors(&parser);
+            assert_eq!(parser.errors.len(), 0);
+            assert!(program.is_some());
+            assert_eq!(program.unwrap(), test.1);
+        }
+    }
+    #[test]
+    fn if_else_expression() {
+        let test_cases = [(
+            "if (x > y) { x } else { y };",
+            Program {
+                statements: vec![Statement::ExpressionStatement(ExpressionStatement::new(
+                    Token::new(TokenType::If),
+                    Expression::IfExpression(IfExpression::new(
+                        TokenType::If,
+                        Expression::InfixExpression(InfixExpression::new(
+                            Token::new(TokenType::GreaterThan),
+                            Expression::Identifier(Identifier::new(TokenType::Ident, "x")),
+                            ">",
+                            Expression::Identifier(Identifier::new(TokenType::Ident, "y")),
+                        )),
+                        BlockStatement::new(
+                            Token::with_value(TokenType::Ident, "x"),
+                            vec![Statement::ExpressionStatement(ExpressionStatement {
+                                token: Token::with_value(TokenType::Ident, "x"),
+                                expression: Expression::Identifier(Identifier::new(
+                                    TokenType::Ident,
+                                    "x",
+                                )),
+                            })],
+                        ),
+                        Some(BlockStatement::new(
+                            Token::new(TokenType::Else),
+                            vec![Statement::ExpressionStatement(ExpressionStatement {
+                                token: Token::with_value(TokenType::Ident, "y"),
+                                expression: Expression::Identifier(Identifier::new(
+                                    TokenType::Ident,
+                                    "y",
+                                )),
+                            })],
+                        )),
+                    )),
+                ))],
+            },
+        )];
+
+        for test in test_cases.iter() {
+            let lexer = Lexer::new(test.0);
+            let mut parser = Parser::new(lexer);
+            let program = parser.parse_program();
+            check_parser_errors(&parser);
+            assert_eq!(parser.errors.len(), 0);
             assert!(program.is_some());
             assert_eq!(program.unwrap(), test.1);
         }