prim_mutators.go

// Copyright 2014 SteelSeries ApS.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// This package implements a basic LISP interpretor for embedding in a go program for scripting.
// This file contains the mutator primitive functions.

package golisp

import ()

func RegisterMutatorPrimitives() {
	MakeSpecialForm("set!", "2", SetVarImpl)
	MakeSpecialForm("set-car!", "2", SetCarImpl)
	MakeSpecialForm("set-cdr!", "2", SetCdrImpl)
	MakeSpecialForm("set-nth!", "3", SetNthImpl)
}

func SetVarImpl(args *Data, env *SymbolTableFrame) (result *Data, err error) {
	symbol := Car(args)
	if !SymbolP(symbol) {
		err = ProcessError("set! requires a raw (unevaluated) symbol as it's first argument.", env)
	}
	value, err := Eval(Cadr(args), env)
	if err != nil {
		return
	}
	return env.SetTo(symbol, value)
}

func SetCarImpl(args *Data, env *SymbolTableFrame) (result *Data, err error) {
	pair, err := Eval(Car(args), env)
	if !PairP(pair) {
		err = ProcessError("set-car! requires a pair as it's first argument.", env)
	}
	value, err := Eval(Cadr(args), env)
	if err != nil {
		return
	}
	ConsValue(pair).Car = value
	return value, nil
}

func SetCdrImpl(args *Data, env *SymbolTableFrame) (result *Data, err error) {
	pair, err := Eval(Car(args), env)
	if !PairP(pair) {
		err = ProcessError("set-cdr! requires a pair as it's first argument.", env)
	}
	value, err := Eval(Cadr(args), env)
	if err != nil {
		return
	}
	ConsValue(pair).Cdr = value

	return value, nil
}

func SetNthImpl(args *Data, env *SymbolTableFrame) (result *Data, err error) {
	l, err := Eval(First(args), env)
	if !ListP(l) {
		err = ProcessError("set-nth! requires a list as it's first argument.", env)
	}
	index, err := Eval(Second(args), env)
	if err != nil {
		return
	}
	value, err := Eval(Third(args), env)
	if err != nil {
		return
	}

	return SetNth(l, int(IntegerValue(index)), value), nil
}