/
functionalExpression.js
76 lines (61 loc) · 2.17 KB
/
functionalExpression.js
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"use strict";
let variables = {
"x": 0,
"y": 1,
"z": 2
};
let cnst = value => () => value;
let expressionVariable = variable => (...args) => args[variables[variable]];
let cachedVariables = {};
Object.keys(variables).forEach(v => cachedVariables[v] = expressionVariable(v));
let variable = v => cachedVariables[v];
let binOperation = op => (a, b) => (...args) => op(a(...args), b(...args));
let multiply = binOperation((a, b) => a * b);
let add = binOperation((a, b) => a + b);
let subtract = binOperation((a, b) => a - b);
let divide = binOperation((a, b) => a / b);
let pi = cnst(Math.PI);
let e = cnst(Math.E);
let avg5 = (...values) =>
(...args) => values.reduce((acc, value) => acc + value(...args), 0)/values.length;
let med3 = (...values) =>
(...args) => values.map(x => x(...args)).sort((a, b) => a - b)[Math.floor(values.length/2)];
let unaryOpeartion = op => a => (...args) => op(a(...args));
let negate = unaryOpeartion(a => -a);
// Parser
let tokens = {}
let addOperation = (token, arity, func) => tokens[token] = {"arity": arity, "func": func};
let addVariables = () => Object.keys(variables).forEach(v => addOperation(v, 0, () => variable(v)));
addOperation("negate", 1, negate);
addOperation("+", 2, add);
addOperation("-", 2, subtract);
addOperation("/", 2, divide);
addOperation("*", 2, multiply);
addOperation("med3", 3, med3);
addOperation("avg5", 5, avg5);
addOperation("pi", 0, () => pi);
addOperation("e", 0, () => e);
addVariables();
let processToken = function(token, stack) {
if(token in tokens) {
var oper = tokens[token];
// console.log(oper);
return oper.func(...stack.splice(stack.length - oper.arity));
} else if(!isNaN(token)) {
return cnst(+token);
} else {
throw new Error("Unkown token: " + token);
}
}
let parseArray = function(arr) {
var stack = [];
for(const token of arr) {
if(token.length == 0) continue;
stack.push(processToken(token, stack));
// console.log(stack);
}
return stack[0];
}
let parse = expressionString => parseArray(expressionString.split(' '));
// console.log(tokens);
console.log(parse("x x *")(2,0,0));