package evaluator import ( "fmt" "monkey/ast" "monkey/object" ) var ( NULL = &object.Null{} TRUE = &object.Boolean{Value: true} FALSE = &object.Boolean{Value: false} ) func Eval(node ast.Node, env *object.Environment) object.Object { switch node := node.(type) { // Statements case *ast.Program: return evalProgram(node, env) case *ast.BlockStatement: return evalBlockStatement(node, env) case *ast.ExpressionStatement: return Eval(node.Expression, env) case *ast.ReturnStatement: val := Eval(node.ReturnValue, env) if isError(val) { return val } return &object.ReturnValue{Value: val} case *ast.LetStatement: val := Eval(node.Value, env) if isError(val) { return val } env.Set(node.Name.Value, val) // Expressions case *ast.IntegerLiteral: return &object.Integer{Value: node.Value} case *ast.Boolean: return nativeBoolToBooleanObject(node.Value) case *ast.PrefixExpression: right := Eval(node.Right, env) if isError(right) { return right } return evalPrefixExpression(node.Operator, right) case *ast.InfixExpression: left := Eval(node.Left, env) if isError(left) { return left } right := Eval(node.Right, env) if isError(right) { return right } return evalInfixExpression(node.Operator, left, right) case *ast.IfExpression: return evalIfExpression(node, env) case *ast.Identifier: return evalIdentifier(node, env) case *ast.FunctionLiteral: params := node.Parameters body := node.Body return &object.Function{Parameters: params, Env: env, Body: body} case *ast.CallExpression: function := Eval(node.Function, env) if isError(function) { return function } args := evalExpressions(node.Arguments, env) if len(args) == 1 && isError(args[0]) { return args[0] } return applyFunction(function, args) } return nil } func evalProgram(program *ast.Program, env *object.Environment) object.Object { var result object.Object for _, statement := range program.Statements { result = Eval(statement, env) switch result := result.(type) { case *object.ReturnValue: return result.Value case *object.Error: return result } } return result } func evalBlockStatement( block *ast.BlockStatement, env *object.Environment, ) object.Object { var result object.Object for _, statement := range block.Statements { result = Eval(statement, env) if result != nil { rt := result.Type() if rt == object.RETURN_VALUE_OBJ || rt == object.ERROR_OBJ { return result } } } return result } func nativeBoolToBooleanObject(input bool) *object.Boolean { if input { return TRUE } return FALSE } func evalPrefixExpression(operator string, right object.Object) object.Object { switch operator { case "!": return evalBangOperatorExpression(right) case "-": return evalMinusPrefixOperatorExpression(right) default: return newError("unknown operator: %s%s", operator, right.Type()) } } func evalInfixExpression( operator string, left, right object.Object, ) object.Object { switch { case left.Type() == object.INTEGER_OBJ && right.Type() == object.INTEGER_OBJ: return evalIntegerInfixExpression(operator, left, right) case operator == "==": return nativeBoolToBooleanObject(left == right) case operator == "!=": return nativeBoolToBooleanObject(left != right) case left.Type() != right.Type(): return newError("type mismatch: %s %s %s", left.Type(), operator, right.Type()) default: return newError("unknown operator: %s %s %s", left.Type(), operator, right.Type()) } } func evalBangOperatorExpression(right object.Object) object.Object { switch right { case TRUE: return FALSE case FALSE: return TRUE case NULL: return TRUE default: return FALSE } } func evalMinusPrefixOperatorExpression(right object.Object) object.Object { if right.Type() != object.INTEGER_OBJ { return newError("unknown operator: -%s", right.Type()) } value := right.(*object.Integer).Value return &object.Integer{Value: -value} } func evalIntegerInfixExpression( operator string, left, right object.Object, ) object.Object { leftVal := left.(*object.Integer).Value rightVal := right.(*object.Integer).Value switch operator { case "+": return &object.Integer{Value: leftVal + rightVal} case "-": return &object.Integer{Value: leftVal - rightVal} case "*": return &object.Integer{Value: leftVal * rightVal} case "/": return &object.Integer{Value: leftVal / rightVal} case "<": return nativeBoolToBooleanObject(leftVal < rightVal) case ">": return nativeBoolToBooleanObject(leftVal > rightVal) case "==": return nativeBoolToBooleanObject(leftVal == rightVal) case "!=": return nativeBoolToBooleanObject(leftVal != rightVal) default: return newError("unknown operator: %s %s %s", left.Type(), operator, right.Type()) } } func evalIfExpression( ie *ast.IfExpression, env *object.Environment, ) object.Object { condition := Eval(ie.Condition, env) if isError(condition) { return condition } if isTruthy(condition) { return Eval(ie.Consequence, env) } else if ie.Alternative != nil { return Eval(ie.Alternative, env) } else { return NULL } } func evalIdentifier( node *ast.Identifier, env *object.Environment, ) object.Object { val, ok := env.Get(node.Value) if !ok { return newError("identifier not found: " + node.Value) } return val } func isTruthy(obj object.Object) bool { switch obj { case NULL: return false case TRUE: return true case FALSE: return false default: return true } } func newError(format string, a ...interface{}) *object.Error { return &object.Error{Message: fmt.Sprintf(format, a...)} } func isError(obj object.Object) bool { if obj != nil { return obj.Type() == object.ERROR_OBJ } return false } func evalExpressions( exps []ast.Expression, env *object.Environment, ) []object.Object { var result []object.Object for _, e := range exps { evaluated := Eval(e, env) if isError(evaluated) { return []object.Object{evaluated} } result = append(result, evaluated) } return result } func applyFunction(fn object.Object, args []object.Object) object.Object { function, ok := fn.(*object.Function) if !ok { return newError("not a function: %s", fn.Type()) } extendedEnv := extendFunctionEnv(function, args) evaluated := Eval(function.Body, extendedEnv) return unwrapReturnValue(evaluated) } func extendFunctionEnv( fn *object.Function, args []object.Object, ) *object.Environment { env := object.NewEnclosedEnvironment(fn.Env) for paramIdx, param := range fn.Parameters { env.Set(param.Value, args[paramIdx]) } return env } func unwrapReturnValue(obj object.Object) object.Object { if returnValue, ok := obj.(*object.ReturnValue); ok { return returnValue.Value } return obj }