evaluator

src/ast/mod.rs

@@ -3,6 +3,7 @@ use crate::token::Token;
 pub trait NodeTrait {
     fn token_literal(&self) -> String;
     fn string(&self) -> String;
+    fn as_any(&self) -> &dyn std::any::Any;
 }
 
 #[allow(dead_code)]
@@ -47,6 +48,10 @@ impl NodeTrait for Expression {
             Expression::CallExpression(i) => i.string(),
         }
     }
+
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
 }
 
 pub struct Program {
@@ -69,6 +74,10 @@ impl NodeTrait for Program {
         }
         out
     }
+
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
 }
 
 pub struct LetStatement {
@@ -102,6 +111,10 @@ impl NodeTrait for LetStatement {
         out.push_str(";");
         out
     }
+
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
 }
 
 impl StatementTrait for LetStatement {
@@ -121,6 +134,10 @@ impl NodeTrait for ReturnStatement {
         out.push_str(";");
         out
     }
+
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
 }
 
 impl StatementTrait for ReturnStatement {
@@ -135,6 +152,10 @@ impl NodeTrait for ExpressionStatement {
     fn string(&self) -> String {
         self.expression.string()
     }
+
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
 }
 
 impl StatementTrait for ExpressionStatement {
@@ -155,6 +176,10 @@ impl NodeTrait for Identifier {
     fn string(&self) -> String {
         self.value.clone()
     }
+
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
 }
 
 #[derive(Debug)]
@@ -171,6 +196,10 @@ impl NodeTrait for IntegerLiteral {
     fn string(&self) -> String {
         self.value.to_string()
     }
+
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
 }
 
 pub struct PrefixExpression {
@@ -190,6 +219,10 @@ impl NodeTrait for PrefixExpression {
         out.push_str(&self.right.string());
         out
     }
+
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
 }
 
 pub struct InfixExpression {
@@ -215,6 +248,10 @@ impl NodeTrait for InfixExpression {
         out.push_str(")");
         out
     }
+
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
 }
 
 pub struct Boolean {
@@ -230,6 +267,10 @@ impl NodeTrait for Boolean {
     fn string(&self) -> String {
         self.value.to_string()
     }
+
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
 }
 
 pub struct IfExpression {
@@ -256,6 +297,10 @@ impl NodeTrait for IfExpression {
         }
         out
     }
+
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
 }
 
 pub struct BlockStatement {
@@ -275,6 +320,10 @@ impl NodeTrait for BlockStatement {
         }
         out
     }
+
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
 }
 
 pub struct FunctionLiteral {
@@ -298,6 +347,10 @@ impl NodeTrait for FunctionLiteral {
         out.push_str(&self.body.string());
         out
     }
+
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
 }
 
 pub struct CallExpression {
@@ -320,4 +373,8 @@ impl NodeTrait for CallExpression {
         out.push_str(")");
         out
     }
+
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
 }

src/evaluator/mod.rs

@@ -0,0 +1,75 @@
+use crate::ast::Program;
+use crate::ast::{self};
+use crate::object::{self, Null, Object};
+
+const NULL: Null = Null;
+const BOOL_TRUE: object::Boolean = object::Boolean { value: true };
+const BOOL_FALSE: object::Boolean = object::Boolean { value: false };
+
+fn eval(node: Box<dyn ast::NodeTrait>) -> Option<Box<dyn object::Object>> {
+    let node = node.as_ref();
+    if let Some(stmt) = node.as_any().downcast_ref::<ast::ExpressionStatement>() {
+        return eval_expression(&stmt.expression);
+    }
+    if let Some(stmt) = node.as_any().downcast_ref::<ast::LetStatement>() {
+        return None;
+    }
+    if let Some(stmt) = node.as_any().downcast_ref::<ast::ReturnStatement>() {
+        return eval_expression(&stmt.return_value);
+    }
+    if let Some(expr) = node.as_any().downcast_ref::<ast::Expression>() {
+        return eval_expression(expr);
+    }
+    if let Some(expr) = node.as_any().downcast_ref::<ast::PrefixExpression>() {
+        let right = &eval(expr.right);
+        return eval_prefix_expression(expr.operator, right);
+    }
+    None
+}
+
+pub fn eval_program(program: Program) -> Option<Box<dyn object::Object>> {
+    let mut res: Option<Box<dyn object::Object>> = None;
+    for stmt in program.statements {
+        res = eval(stmt)
+    }
+    res
+}
+
+fn eval_expression(expression: &ast::Expression) -> Option<Box<dyn object::Object>> {
+    match expression {
+        ast::Expression::IntegerLiteral(int) => {
+            Some(Box::new(object::Integer { value: int.value }))
+        }
+        ast::Expression::Boolean(b) => Some(Box::new(native_bool_to_bool_object(b.value))),
+        _ => None,
+    }
+}
+
+fn eval_prefix_expression(
+    operator: String,
+    right: &Option<Box<dyn object::Object>>,
+) -> Option<Box<dyn object::Object>> {
+    match operator.as_str() {
+        "!" => eval_bang_operator_expression(right),
+        _ => Some(Box::new(NULL)),
+    }
+}
+
+fn eval_bang_operator_expression(
+    right: &Option<Box<dyn object::Object>>,
+) -> Option<Box<dyn object::Object>> {
+    let bool_true = Box::new(BOOL_TRUE);
+    let bool_false = Box::new(BOOL_FALSE);
+    let null = Box::new(NULL);
+
+    match right..unwrap() {
+        bool_true => Some(bool_false),
+        bool_false => Some(bool_true),
+        null => Some(bool_true),
+        _ => Some(bool_false),
+    }
+}
+
+fn native_bool_to_bool_object(input: bool) -> object::Boolean {
+    if input { BOOL_TRUE } else { BOOL_FALSE }
+}

src/main.rs

@@ -1,5 +1,7 @@
 mod ast;
+mod evaluator;
 mod lexer;
+mod object;
 mod parser;
 mod repl;
 mod token;

src/object/mod.rs

@@ -0,0 +1,50 @@
+pub enum ObjectType {
+    INTEGER,
+    BOOLEAN,
+    NULL,
+}
+
+pub trait Object {
+    fn object_type(&self) -> ObjectType;
+    fn inspect(&self) -> String;
+}
+
+pub struct Integer {
+    pub value: i64,
+}
+
+impl Object for Integer {
+    fn object_type(&self) -> ObjectType {
+        ObjectType::INTEGER
+    }
+
+    fn inspect(&self) -> String {
+        self.value.to_string()
+    }
+}
+
+pub struct Boolean {
+    pub value: bool,
+}
+
+impl Object for Boolean {
+    fn object_type(&self) -> ObjectType {
+        ObjectType::BOOLEAN
+    }
+
+    fn inspect(&self) -> String {
+        self.value.to_string()
+    }
+}
+
+pub struct Null;
+
+impl Object for Null {
+    fn object_type(&self) -> ObjectType {
+        ObjectType::NULL
+    }
+
+    fn inspect(&self) -> String {
+        "null".to_string()
+    }
+}

src/repl/mod.rs

@@ -1,4 +1,4 @@
-use crate::ast::NodeTrait;
+use crate::evaluator;
 use crate::lexer::new;
 use crate::parser::Parser;
 use crate::parser::new_parser;
@@ -20,11 +20,13 @@ pub fn start_repl() {
         let lexer = new(input.to_string());
         let mut parser: Parser = new_parser(lexer);
         let program = parser.parse_program();
+        let evaluated = evaluator::eval_program(program);
 
         for err in parser.errors() {
             eprintln!("ERROR: {}", err);
         }
-
-        println!("{}", program.string());
+        if !evaluated.is_none() {
+            println!("{}", evaluated.unwrap().inspect());
+        }
     }
 }