Built-in functions:
len() added git-svn-id: https://svn.tlawal.org/svn/monkey@59 f6afcba9-9ef1-4bdd-9b72-7484f5705bac
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19
evaluator/builtins.go
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19
evaluator/builtins.go
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@ -0,0 +1,19 @@
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package evaluator
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import "monkey/object"
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var builtins = map[string]*object.Builtin{
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"len": &object.Builtin{
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Fn: func(args ...object.Object) object.Object {
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if len(args) != 1 {
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return new_error("wrong number of arguments, got=%d, want=1", len(args))
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}
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switch arg := args[0].(type) {
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case *object.String:
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return &object.Integer{Value: int64(len(arg.Value))}
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default:
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return new_error("argument to `len` not supported, got %s", args[0].Type())
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}
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},
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},
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}
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@ -111,14 +111,18 @@ func eval_program(program *ast.Program, env *object.Environment) object.Object {
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}
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func apply_function(fn object.Object, args []object.Object) object.Object {
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function, ok := fn.(*object.Function)
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if !ok {
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switch fn := fn.(type) {
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case *object.Function:
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extended_env := extend_function_env(fn, args)
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evaluated := Eval(fn.Body, extended_env)
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return unwrap_return_value(evaluated)
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case *object.Builtin:
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return fn.Fn(args...)
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default:
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return new_error("not a function: %s", fn.Type())
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}
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extended_env := extend_function_env(function, args)
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evaluated := Eval(function.Body, extended_env)
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return unwrap_return_value(evaluated)
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}
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func extend_function_env(fn *object.Function, args []object.Object) *object.Environment {
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@ -151,11 +155,14 @@ func eval_expression(expressions []ast.Expression, env *object.Environment) []ob
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}
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func eval_identifier(node *ast.Identifier, env *object.Environment) object.Object {
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val, ok := env.Get(node.Value)
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if !ok {
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return new_error("identifier not found: " + node.Value)
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if val, ok := env.Get(node.Value); ok {
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return val
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}
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return val
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if builtin, ok := builtins[node.Value]; ok {
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return builtin
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}
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return new_error("identifier not found: " + node.Value)
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}
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func eval_block_statement(block *ast.BlockStatement, env *object.Environment) object.Object {
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@ -267,8 +274,8 @@ func eval_integer_infix_expression(operator string, left object.Object, right ob
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}
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/*
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FEATURES TODO:
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- Add support for string comparision '==' and '!='.
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FEATURES TODO:
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- Add support for string comparision '==' and '!='.
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*/
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func eval_string_infix_expression(operator string, left object.Object, right object.Object) object.Object {
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if operator != "+" {
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@ -268,6 +268,37 @@ func TestStringConcatenation(l_test *testing.T) {
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}
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}
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func TestBuiltinFunctions(l_test *testing.T) {
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tests := []struct {
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input string
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expected interface{}
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}{
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{`len("")`, 0},
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{`len("four")`, 4},
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{`len("hello world")`, 11},
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{`len(1)`, "argument to `len` not supported, got INTEGER"},
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{`len("one", "two")`, "wrong number of arguments, got=2, want=1"},
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}
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for _, tt := range tests {
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evaluated := test_eval(tt.input)
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switch expected := tt.expected.(type) {
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case int:
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test_integer_object(l_test, evaluated, int64(expected))
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case string:
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error_object, ok := evaluated.(*object.Error)
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if !ok {
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l_test.Errorf("object is not Error, got=%T (%+v)", evaluated, evaluated)
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continue
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}
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if error_object.Message != expected {
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l_test.Errorf("wrong error message, expected=%q, got=%q", expected, error_object.Message)
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}
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}
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}
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}
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// Helpers
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func test_eval(input string) object.Object {
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l_lexer := lexer.New(input)
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@ -139,9 +139,9 @@ func is_digit(ch byte) bool {
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}
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/*
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Read the current character until it encounters a closing '"' or end of input.
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TODO: some additional thing that can be done at the lexer level with strings is to report an error when it
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reaches the end of input without proper termination. Support for character escaping would be really neat.
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Read the current character until it encounters a closing '"' or end of input.
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TODO: some additional thing that can be done at the lexer level with strings is to report an error when it
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reaches the end of input without proper termination. Support for character escaping would be really neat.
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*/
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func (l_lexer *Lexer) read_string() string {
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position := l_lexer.position + 1
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@ -18,30 +18,30 @@ func NewEnvironment() *Environment {
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}
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/*
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Enclosing Environments
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Enclosing Environments
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Here is a problem case, lets say in monkey I would want to type this:
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Here is a problem case, lets say in monkey I would want to type this:
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```
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let i = 5;
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let print_num = fn(i) {
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puts(i);
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}
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```
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let i = 5;
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let print_num = fn(i) {
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puts(i);
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}
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print_num(10);
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puts(i);
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```
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print_num(10);
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puts(i);
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```
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The ideal result of the above code in the monkey programming language is for 10 and 5 to be the outputs respectively.
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In a situation where enclosed environment does not exists, both outputs will be 10 because the current value of i
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would be overwritten. The ideal situation would be to preserve the previous binding to 'i' while also making a a new
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one.
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The ideal result of the above code in the monkey programming language is for 10 and 5 to be the outputs respectively.
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In a situation where enclosed environment does not exists, both outputs will be 10 because the current value of i
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would be overwritten. The ideal situation would be to preserve the previous binding to 'i' while also making a a new
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one.
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This works be creating a new instance of object.Environment with a pointer to the environment it should extend, doing this
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encloses a fresh and empty environment with an existing one. When the Get method is called and it itself doesn't have the value
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associated with the given name, it calls the Get of the enclosing environment. That's the environment it's extending. If that
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enclosing environment can't find the value, it calls its own enclosing environment and so on until there is no enclosing environment
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anymore and it will error out to an unknown identifier.
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This works be creating a new instance of object.Environment with a pointer to the environment it should extend, doing this
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encloses a fresh and empty environment with an existing one. When the Get method is called and it itself doesn't have the value
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associated with the given name, it calls the Get of the enclosing environment. That's the environment it's extending. If that
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enclosing environment can't find the value, it calls its own enclosing environment and so on until there is no enclosing environment
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anymore and it will error out to an unknown identifier.
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*/
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func NewEnclosedEnvironment(outer *Environment) *Environment {
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env := NewEnvironment()
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@ -17,6 +17,7 @@ const (
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ERROR_OBJECT = "ERROR"
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FUNCTION_OBJECT = "FUNCTION"
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STRING_OBJECT = "STRING"
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BUILTIN_OBJ = "BUILTIN"
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)
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type Object interface {
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@ -110,3 +111,18 @@ type String struct {
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func (s *String) Type() ObjectType { return STRING_OBJECT }
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func (s *String) Inspect() string { return s.Value }
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// Builtin Functions
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type BuiltinFunction func(args ...Object) Object
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type Builtin struct {
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Fn BuiltinFunction
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}
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func (b *Builtin) Type() ObjectType {
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return BUILTIN_OBJ
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}
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func (b *Builtin) Inspect() string {
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return "Builtin Function"
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}
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