Monkey/evaluator/builtins.go

package evaluator

import "github/runnignwater/monkey/object"

// 内建函数
var builtins = map[string]*object.Builtin{
	"len": {
		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.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", args[0].Type())
			}
		},
	},
	"first": {
		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.ArrayObj {
				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": {
		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.ArrayObj {
				return newError("argument to `first` 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
		},
	},
	// rest returns a new array containing all elements of the array passed as argument, except the first one
	// >> let a = [1, 2, 3, 4];
	// >> rest(a)
	// [2, 3, 4]
	// >> rest(rest(a))
	// [3, 4]
	// >> rest(rest(rest(a)))
	// [4]
	// >> rest(rest(rest(rest(a))))
	// []
	// >> rest(rest(rest(rest(rest(a)))))
	// null
	"rest": {
		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.ArrayObj {
				return newError("argument to `first` must be ARRAY, got %s", args[0].Type())
			}

			arr := args[0].(*object.Array)
			length := len(arr.Elements)
			if length > 0 {
				newElements := make([]object.Object, length-1, length-1)
				copy(newElements, arr.Elements[1:length])
				return &object.Array{Elements: newElements}
			}
			return NULL
		},
	},
	// It adds a new element to the end of the array. But, and here's the kicker, it doesn't modify the given array.
	// Instead, it allocates a new array with the same elements as the old one plus the new, pushed element.
	// >> let a = [1, 2, 3, 4];
	// >> let b = push(a, 5);
	// >> a
	//[1, 2, 3, 4]
	// >> b
	//[1, 2, 3, 4, 5]
	"push": {
		Fn: func(args ...object.Object) object.Object {
			if len(args) != 2 {
				return newError("wrong number of arguments. got=%d, want=1", len(args))
			}
			if args[0].Type() != object.ArrayObj {
				return newError("argument to `first` must be ARRAY, got %s", args[0].Type())
			}

			arr := args[0].(*object.Array)
			length := len(arr.Elements)

			newElements := make([]object.Object, length+1, length+1)
			copy(newElements, arr.Elements)
			newElements[length] = args[1]

			return &object.Array{Elements: newElements}
		},
	},
}