本文主要是介绍js实现一个粗略的四则运算解释器，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
这样的一个解释器几乎没用，不过只是为了学习一下解释器的知识，有空继续学习。
支持纯变量的解释，解释器第一个参数为纯变量的字符串，第二个参数为解释上下文，也就是变量的值。
支持四则运算，括号
function Context(map) {this.map = map;
}Context.prototype.getContext = function() {return this.map;
}var context;function AbstractExpression() {}
AbstractExpression.prototype.interpret = function() {}function TerminalExpression(val) {this.val = val;
}TerminalExpression.prototype = new AbstractExpression();
TerminalExpression.prototype.interpret = function(isRaw) {if (!isNaN(+this.val)) {return this.val;}var result = context.getContext()[this.val];if (!result) {throw new Error('');return;}return result;
}function NonTerminalExpression(left, right) {this.left = left;this.right = right;
}NonTerminalExpression.prototype = new AbstractExpression();
NonTerminalExpression.prototype.interpret = function() {
}function AddExpression(left, right) {NonTerminalExpression.call(this, left, right);
}AddExpression.prototype = new NonTerminalExpression();
AddExpression.prototype.interpret = function() {return this.left.interpret() + this.right.interpret();
}function SubExpression(left, right) {NonTerminalExpression.call(this, left, right);
}SubExpression.prototype = new NonTerminalExpression();
SubExpression.prototype.interpret = function() {return this.left.interpret() - this.right.interpret();
}function MulExpression(left, right) {NonTerminalExpression.call(this, left, right);
}MulExpression.prototype = new NonTerminalExpression();
MulExpression.prototype.interpret = function() {return this.left.interpret() * this.right.interpret();
}function DivExpression(left, right) {NonTerminalExpression.call(this, left, right);
}DivExpression.prototype = new NonTerminalExpression();
DivExpression.prototype.interpret = function() {return this.left.interpret() / this.right.interpret();
}function BracketExpression(val) {this.val = val;
}BracketExpression.prototype = new NonTerminalExpression();
BracketExpression.prototype.interpret = function() {var val = this.val.replace(/^\((.+)\)$/, '$1');var parser = new Parser();var root = parser.parse(val);if (!root) {return;}return root.interpret();
}function Interpreter(expression, contextEnv) {this.parser = new Parser();this.expression = expression;context = new Context(contextEnv);this.root = null;
}Interpreter.prototype.run = function() {this.root = this.parser.parse(this.expression);if (!this.root) {return;}var result = this.interpret();console.log(result);
}Interpreter.prototype.interpret = function() {return this.root.interpret();
}function Parser() {}
Parser.prototype.parse = function(expression) {var iterator = new Iterator(expression);var root = null;var i = 0;var len = expression.length;var next, left, right;var current;var tmp = '';var stack = [];var map = {'+': AddExpression,'-': SubExpression,'*': MulExpression,'/': DivExpression};while(iterator.hasNext()) {current = iterator.nextToken(/[^\s]/);if (current === false) {return root;}switch(current) {case '(': tmp = '(';stack.push('(');while(iterator.hasNext()) {current = iterator.nextToken(/[^\s]/);if (current === false) {throw new Error('');return;}if (current === '(') {stack.push('(');}if (current === ')') {stack.pop();tmp += current;if (stack.length === 0) {break;} else {continue;}}tmp += current;}if (root === null) {root = new BracketExpression(tmp);} else {root.right = new BracketExpression(tmp);}break;case '+':case '-':case '*':case '/':left = root;if (left === null) {left = new TerminalExpression(0);}next = iterator.nextToken(/[^\s]/);if (next === false) {throw new Error('');return;}if (next === '(') {iterator.rollback();right = new TerminalExpression(null);} else if (/[0-9]/.test(next)){throw new Error('');} else {right = next;while(next = iterator.nextToken(/[^\s]/)) {if (/[a-zA-Z0-9]/.test(next)) {right += next;} else {iterator.rollback();break;}}right = new TerminalExpression(right);}if ( (current === '*' || current === '/') && (left instanceof AddExpression || left instanceof SubExpression)) {left.right = new map[current](left.right, right);root = left;break;}root = new map[current](left, right);break;default: root = new TerminalExpression(current);}i++;}return root;
}function Iterator(val) {this.val = val;this.postion = 0;this.length = val.length;
}
Iterator.prototype.next = function() {return this.val[this.postion++];
}Iterator.prototype.hasNext = function() {return this.postion < this.length;
}Iterator.prototype.rollback = function() {return this.postion--;
}Iterator.prototype.nextToken = function(regexp) {while(this.hasNext()) {var current = this.next();if (regexp.test(current)) {return current;}}return false;
}new Interpreter('( ((a +b) + (c * a + (a* cc- bx )))) ',{a:1,b:2,c:3,bx:1,cc:2}).run();这篇关于js实现一个粗略的四则运算解释器的文章就介绍到这儿，希望我们推荐的文章对编程师们有所帮助！
