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path: root/ops.go
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package main

import (
	"container/list"
	"fmt"
	"log"
)

type (
	List    struct{ *list.List }
	Element struct{ *list.Element }
)

var (
	alphabet  List
	zero, one Element
)

func init() {
	alphabet = List{list.New()}
	for i := 0; i <= maxValue; i++ {
		alphabet.PushBack(i)
	}
	zero = Element{alphabet.Front()}
	one = Element{zero.Next()}
}

// next returns next char in alphabet
func (n Element) next() Element {
	if nxt := n.Next(); nxt != nil {
		return Element{nxt}
	}
	log.Fatal("out of range", n.Value)
	return Element{}
}

// prev returns previous char in alphabet
func (n Element) prev() Element {
	if prv := n.Prev(); prv != nil {
		return Element{prv}
	}
	return zero
}

// add defines addition
func add(m, n Element) Element {
	if m == zero {
		return n
	}
	return add(m.prev(), n).next()
}

// times defines mutiplication
func times(m, n Element) Element {
	if m == zero {
		return zero
	}
	return add(times(m.prev(), n), n)
}

// pot defines power function
func pot(m, n Element) Element {
	if n == zero {
		return one
	}
	return times(pot(m, n.prev()), m)
}

// sub defines substraction
func sub(m, n Element) Element {
	if n == zero {
		return m
	}
	return sub(m, n.prev()).prev()
}

// scan lookups n-th element representation
func scan(n int) Element {
	if n > alphabet.Len() {
		log.Fatal("out of range")
		return Element{}
	}
	e := alphabet.Front()
	for i := 0; i < n; i++ {
		e = e.Next()
	}
	return Element{e}
}

// String pretty-prints value
func (n Element) String() string {
	return fmt.Sprint(n.Value)
}