postfix.js
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var Mexp=require('./lexer.js');
Mexp.prototype.toPostfix = function () {
'use strict';
var post=[],elem,popped,prep,pre,ele;
var stack=[{value:"(",type:4,pre:0}];
var arr=this.value;
for (var i=1; i < arr.length; i++) {
if(arr[i].type===1||arr[i].type===3||arr[i].type===13){ //if token is number,constant,or n(which is also a special constant in our case)
if(arr[i].type===1)
arr[i].value=Number(arr[i].value);
post.push(arr[i]);
}
else if(arr[i].type===4){
stack.push(arr[i]);
}
else if(arr[i].type===5){
while((popped=stack.pop()).type!==4){
post.push(popped);
}
}
else if(arr[i].type===11){
while((popped=stack.pop()).type!==4){
post.push(popped);
}
stack.push(popped);
}
else {
elem=arr[i];
pre=elem.pre;
ele=stack[stack.length-1];
prep=ele.pre;
var flag=ele.value=='Math.pow'&&elem.value=='Math.pow';
if(pre>prep)stack.push(elem);
else {
while(prep>=pre&&!flag||flag&&pre<prep){
popped=stack.pop();
ele=stack[stack.length-1];
post.push(popped);
prep=ele.pre;
flag=elem.value=='Math.pow'&&ele.value=='Math.pow';
}
stack.push(elem);
}
}
}
return new Mexp(post);
};
module.exports=Mexp;