区間加算
(functional/range_add_and_range_sum.hpp)

#pragma once
#include"../alga/maybe.hpp"

/**
 * @brief 区間加算
 */

template<typename T,typename E>
struct range_add_and_range_sum{
    T operator()(const maybe<T>& s,const E& t,int l,int r){
        return s.unwrap_or(T())+t*(r-l);
    }
};

#line 2 "alga/maybe.hpp"
#include<cassert>

/**
 * @brief Maybe
 * @see https://ja.wikipedia.org/wiki/%E3%83%A2%E3%83%8A%E3%83%89_(%E3%83%97%E3%83%AD%E3%82%B0%E3%83%A9%E3%83%9F%E3%83%B3%E3%82%B0)#Maybe%E3%83%A2%E3%83%8A%E3%83%89
 */

template<typename T>
struct maybe{
    bool _is_none;
    T val;
    maybe():_is_none(true){}
    maybe(T val):_is_none(false),val(val){}
    T unwrap()const{
        assert(!_is_none);
        return val;
    }
    T unwrap_or(T e)const{
        return _is_none?e:val;
    }
    bool is_none()const{return _is_none;}
    bool is_some()const{return !_is_none;}
};

template<typename T,typename F>
auto expand(F op){
    return [&op](const maybe<T>& s,const maybe<T>& t){
        if(s.is_none())return t;
        if(t.is_none())return s;
        return maybe<T>(op(s.unwrap(),t.unwrap()));
    };
}
#line 3 "functional/range_add_and_range_sum.hpp"

/**
 * @brief 区間加算
 */

template<typename T,typename E>
struct range_add_and_range_sum{
    T operator()(const maybe<T>& s,const E& t,int l,int r){
        return s.unwrap_or(T())+t*(r-l);
    }
};