errors.go

/* errors.go - Go wrapper for Emacs module API.

Copyright (C) 2016 Yann Hodique <yann.hodique@gmail.com>.

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at
your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

package emacs

import "errors"

type nonLocalExit interface {
	error
	Symbol() Symbol
	Value() Value
}

type signal interface {
	nonLocalExit
	isSignal() bool
}

type throw interface {
	nonLocalExit
	isThrow() bool
}

type nonLocalExitImpl struct {
	symbol Symbol
	value  Value
}

func (e *nonLocalExitImpl) Error() string {
	return "emacs non-local exit"
}

func (e *nonLocalExitImpl) Symbol() Symbol {
	return e.symbol
}

func (e *nonLocalExitImpl) Value() Value {
	return e.value
}

var _ nonLocalExit = (*nonLocalExitImpl)(nil)

type signalImpl struct {
	nonLocalExitImpl
}

func (s *signalImpl) isSignal() bool { return true }

var _ signal = (*signalImpl)(nil)

type throwImpl struct {
	nonLocalExitImpl
}

func (s *throwImpl) isThrow() bool { return true }

var _ throw = (*throwImpl)(nil)

func isSignal(err error) bool {
	_, ok := err.(signal)
	return ok
}

func isThrow(err error) bool {
	_, ok := err.(throw)
	return ok
}

// Signal performs a signaled non-local exit
func Signal(sym Symbol, val Value) (Value, error) {
	return nil, &signalImpl{
		nonLocalExitImpl{
			symbol: sym,
			value:  val,
		},
	}
}

// Throw performs a thrown non-local exit
func Throw(sym Symbol, val Value) (Value, error) {
	return nil, &throwImpl{
		nonLocalExitImpl{
			symbol: sym,
			value:  val,
		},
	}
}

// Error provides shortcut for common error pattern
func Error(msg string) (Value, error) {
	return nil, errors.New(msg)
}