--

"use strict"
// I rewrote this task. Notes copied form prev.
// :NOTE: operands should be referred to prototype of BinExp
// :NOTE: copy-paste code for prototype assignment

function Const(val){
    this.val = val;
}
Const.prototype.evaluate = function(x, y, z){
    return this.val;
};
Const.prototype.toString = function(){
    return this.val + "";
};

function Variable(val){
    this.val = val;
}
Variable.prototype.evaluate = function(x, y, z){
            let a = {"x" : x, "y" : y, "z" : z};
            return a[this.val];
        };
Variable.prototype.toString = function(){
    return this.val;
}

let AbstractExpression = {
    evaluate : function(x, y, z){return this.operation(...this.operands.map((currentValue) => {
        return currentValue.evaluate(x, y, z);
    }))},
    "toString" : function(){
        let result = "";
        for(let i of this.operands){
            result += i.toString() + " ";
        }
        return result + this.sign;
    }
}

function Operation(operation, sign){
    let op = function(...operands) {
        this.operands = operands;
    }
    op.prototype = Object.create(AbstractExpression);
    op.prototype.operation = operation;
    op.prototype.sign = sign;
    return op;
}
//===============base==============
let Add = Operation((a, b) => (a+b), "+");
let Subtract = Operation((a,b) => (a-b), "-");
let Multiply = Operation((a,b) => a*b, "*");
let Divide = Operation((a, b) => a/b, "/")p;
let Negate = Operation((a) => -a, "negate");
//==============easy============
let Sinh = Operation((a) => Math.sinh(a), "sinh");
let Cosh = Operation((a) => Math.cosh(a), "cosh");