monkey/object/builtins.go

package object

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"unicode/utf8"
)

var Builtins = []struct {
	Name    string
	Builtin *Builtin
}{
	{
		"len",
		&Builtin{Fn: func(args ...Object) Object {
			if len(args) != 1 {
				return newError("wrong number of arguments. got=%d, want=1",
					len(args))
			}

			switch arg := args[0].(type) {
			case *Array:
				return &Integer{Value: int64(len(arg.Elements))}
			case *String:
				return &Integer{Value: int64(utf8.RuneCountInString(arg.Value))}
			default:
				return newError("argument to `len` not supported, got %s",
					args[0].Type())
			}
		},
		},
	},
	{
		"input",
		&Builtin{Fn: func(args ...Object) Object {
			if len(args) > 0 {
				obj, ok := args[0].(*String)
				if !ok {
					return newError(
						"argument to `input` not supported, got %s",
						args[0].Type(),
					)
				}
				fmt.Fprintf(os.Stdout, obj.Value)
			}

			buffer := bufio.NewReader(os.Stdin)

			line, _, err := buffer.ReadLine()
			if err != nil && err != io.EOF {
				return newError(fmt.Sprintf("error reading input from stdin: %s", err))
			}
			return &String{Value: string(line)}
		}},
	},
	{
		"print",
		&Builtin{Fn: func(args ...Object) Object {
			for _, arg := range args {
				fmt.Println(arg.Inspect())
			}

			return nil
		},
		},
	},
	{
		"first",
		&Builtin{Fn: func(args ...Object) Object {
			if len(args) != 1 {
				return newError("wrong number of arguments. got=%d, want=1", len(args))
			}
			if args[0].Type() != ARRAY_OBJ {
				return newError("argument to `first` must be ARRAY, got %s", args[0].Type())
			}

			arr := args[0].(*Array)
			if len(arr.Elements) > 0 {
				return arr.Elements[0]
			}

			return nil
		},
		},
	},
	{
		"last",
		&Builtin{Fn: func(args ...Object) Object {
			if len(args) != 1 {
				return newError("wrong number of arguments. got=%d, want=1", len(args))
			}
			if args[0].Type() != ARRAY_OBJ {
				return newError("argument to `last` must be ARRAY, got %s", args[0].Type())
			}

			arr := args[0].(*Array)
			length := len(arr.Elements)
			if length > 0 {
				return arr.Elements[length-1]
			}

			return nil
		},
		},
	},
	{
		"rest",
		&Builtin{Fn: func(args ...Object) Object {
			if len(args) != 1 {
				return newError("wrong number of arguments. got=%d, want=1",
					len(args))
			}
			if args[0].Type() != ARRAY_OBJ {
				return newError("argument to `rest` must be ARRAY, got %s",
					args[0].Type())
			}

			arr := args[0].(*Array)
			length := len(arr.Elements)
			if length > 0 {
				newElements := make([]Object, length-1, length-1)
				copy(newElements, arr.Elements[1:length])
				return &Array{Elements: newElements}
			}

			return nil
		},
		},
	},
	{
		"push",
		&Builtin{Fn: func(args ...Object) Object {
			if len(args) != 2 {
				return newError("wrong number of arguments. got=%d, want=2",
					len(args))
			}
			if args[0].Type() != ARRAY_OBJ {
				return newError("argument to `push` must be ARRAY, got %s",
					args[0].Type())
			}

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

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

			return &Array{Elements: newElements}
		},
		},
	},
	{
		"pop",
		&Builtin{Fn: func(args ...Object) Object {
			if len(args) != 1 {
				return newError("wrong number of arguments. got=%d, want=1",
					len(args))
			}
			if args[0].Type() != ARRAY_OBJ {
				return newError("argument to `pop` must be ARRAY, got %s",
					args[0].Type())
			}

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

			if length == 0 {
				return newError("cannot pop from an empty array")
			}

			element := arr.Elements[length-1]
			arr.Elements = arr.Elements[:length-1]

			return element
		},
		},
	},
	{
		"exit",
		&Builtin{Fn: func(args ...Object) Object {
			if len(args) == 1 {
				if args[0].Type() != INTEGER_OBJ {
					return newError("argument to `exit` must be INTEGER, got %s",
						args[0].Type())
				}
				os.Exit(int(args[0].(*Integer).Value))
			} else {
				os.Exit(0)
			}
			return nil
		},
		},
	},
}

func newError(format string, a ...interface{}) *Error {
	return &Error{Message: fmt.Sprintf(format, a...)}
}

func GetBuiltinByName(name string) *Builtin {
	for _, def := range Builtins {
		if def.Name == name {
			return def.Builtin
		}
	}
	return nil
}