Monkey

A go implementation of the Monkey Language

Following both books, it implements the interpreter and the compiler

My code is shorter as I used high order functions in some places to reduce code duplication, i.e.:

Original

var builtins = map[string]*object.Builtin{
    "len": &object.Builtin{Fn: func(args ...object.Object) object.Object {
        if len(args) != 1 {
            return newError("wrong number of arguments. got=%d, want=1",
                len(args))
        }
        switch arg := args[0].(type) {
        case *object.Array:
            return &object.Integer{Value: int64(len(arg.Elements))}
        case *object.String:
            return &object.Integer{Value: int64(len(arg.Value))}
        default:
            return newError("argument to `len` not supported, got %s",
                args[0].Type())
        }
    },
    },
    "first": &object.Builtin{
        Fn: func(args ...object.Object) object.Object {
            if len(args) != 1 {
                return newError("wrong number of arguments. got=%d, want=1",
                    len(args))
            }
            if args[0].Type() != object.ARRAY_OBJ {
                return newError("argument to `first` must be ARRAY, got %s",
                    args[0].Type())
            }
            arr := args[0].(*object.Array)
            if len(arr.Elements) > 0 {
                return arr.Elements[0]
            }
            return NULL
        },
    },
    "last": &object.Builtin{
        Fn: func(args ...object.Object) object.Object {
            if len(args) != 1 {
                return newError("wrong number of arguments. got=%d, want=1",
                    len(args))
            }
            if args[0].Type() != object.ARRAY_OBJ {
                return newError("argument to `last` must be ARRAY, got %s",
                    args[0].Type())
            }
            arr := args[0].(*object.Array)
            length := len(arr.Elements)
            if length > 0 {
                return arr.Elements[length-1]
            }
            return NULL
        },
    },

Refactored

func argSizeCheck(expectedSize int, args []object.Object, body func([]object.Object) object.Object) object.Object {
    argsLength := len(args)
    if argsLength != expectedSize {
        return newError("wrong number of arguments. got=%d, want=1", argsLength)
    }
    return body(args)
}
func arrayCheck(builtinName string, args []object.Object, body func(*object.Array, int) object.Object) object.Object {
    if args[0].Type() != object.ArrayObj {
        return newError("argument to `%s` must be ARRAY, got %s", builtinName, args[0].Type())
    }
    arr := args[0].(*object.Array)
    return body(arr, len(arr.Elements))
}
var builtins = map[string]*object.Builtin{
    "len": {
        Fn: func(args ...object.Object) object.Object {
            return argSizeCheck(1, args, func(args []object.Object) object.Object {
                switch arg := args[0].(type) {
                case *object.String:
                    return &object.Integer{Value: int64(len(arg.Value))}
                case *object.Array:
                    return &object.Integer{Value: int64(len(arg.Elements))}
                default:
                    return newError("argument to `len` not supported, got %s", arg.Type())
                }
            })
        }},
    "first": {
        Fn: func(args ...object.Object) object.Object {
            return argSizeCheck(1, args, func(args []object.Object) object.Object {
                return arrayCheck("first", args, func(arr *object.Array, length int) object.Object {
                    if length > 0 {
                        return arr.Elements[0]
                    }
                    return NULL
                })
            })
        },
    },
    "last": {
        Fn: func(args ...object.Object) object.Object {
            return argSizeCheck(1, args, func(args []object.Object) object.Object {
                return arrayCheck("last", args, func(arr *object.Array, length int) object.Object {
                    if length > 0 {
                        return arr.Elements[length-1]
                    }
                    return NULL
                })
            })
        },
    },

Running

Build the executable with:

$ go build -o monkey .

And run it with:

$ ./monkey

Benchmarks

Build the benchmark with:

$ go build -o fibonacci ./benchmark

And run it with:

$ ./fibonacci

You can pass two additional parameters:

• engine with two possible values: vm and eval.
• algo with two possible values: slow and fast.

$ ./fibonacci --engine=eval

Tests

Run the tests with:

$ go test ./...