Evaluates well-formed reverse polish notation expressions (http://en.wikipedia.org/wiki/Reverse_Polish_notation).
Strings with tokens separated by single spaces. Tokens are operators or operands. Operators are +, -, * or /. Operands are integers or floats (e.g. 7, 3.23, -1e9).
The value of the evaluated expression.
"1 1 +" -> 2
"5 8 -" -> -3
"2 3 7 + -" -> -8
"5 3 * 5 +" -> 20
| function(a, // The input string | |
| b) { // Placeholder var that will become the stack | |
| return (b = [])[ // Create an empty stack, and later return its 0th element (*) | |
| a.replace(/\S+/g, // For each token (everything that does not | |
| // contain spaces) in the string, | |
| function(c) { // inspect and act on it: | |
| b.push( // Something will always be pushed to the stack: | |
| +c || // If it is a number (an operand), push the number itself. | |
| eval( // Else it is an operator. | |
| b.pop(a = b.pop()) + // Pop the topmost element and save it in a. | |
| // Then pop the next element and | |
| c + // apply the operator together with the | |
| a)) // previously saved element. | |
| }), | |
| 0] // (*) After going through all tokens, index the 0th element | |
| // of the stack. This is the result of the expression. | |
| } |
| function(a,b){return(b=[])[a.replace(/\S+/g,function(c){b.push(+c==c?c:eval(b.pop(a=b.pop())+c+a))}),0]} |
| DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE | |
| Version 2, December 2004 | |
| Copyright (C) 2011 YOUR_NAME_HERE <YOUR_URL_HERE> | |
| Everyone is permitted to copy and distribute verbatim or modified | |
| copies of this license document, and changing it is allowed as long | |
| as the name is changed. | |
| DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE | |
| TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION | |
| 0. You just DO WHAT THE FUCK YOU WANT TO. |
| { | |
| "name": "rpn", | |
| "description": "Reverse Polish Notation expression evaluator", | |
| "keywords": [ | |
| "expression", | |
| "parser", | |
| "rpn", | |
| "evaluator" | |
| ] | |
| } |
| <!DOCTYPE html> | |
| <title>RPN</title> | |
| <div>Expected value: <b>3, -4, -8, 14</b></div> | |
| <div>Actual value: <b id="ret"></b></div> | |
| <script> | |
| // write a small example that shows off the API for your example | |
| // and tests it in one fell swoop. | |
| var myFunction = function(a,b){return(b=[])[a.replace(/\S+/g,function(c){b.push(+c==c?c:eval(b.pop(a=b.pop())+c+a))}),0]} | |
| document.getElementById( "ret" ).innerHTML = [myFunction('1 2 +'), myFunction('2 6 -'), myFunction('2 3 7 + -'), myFunction('5 1 2 + 4 * + 3 -')].join(', '); | |
| </script> |
Maybe start with removing useless parenthesis, semi-colons and apply other common tricks...
Please do! I honestly thought I had to keep those semi-colons at least...
Edit: Ah, there's was one at the end.
But I see I left a space by mistake. I'll remove that one.
In each case you pop 2 values from the stack. I guess you could cut some bits doing it only once at the beginning of the loop. A while(j--) loop could be shorter (but reversed). There's a lot of extra parenthesis and some semi-colons. The ternary operator (?:) is shorter than &&||.
Have fun!
function(i,s,t,j,e){i=i.split(' ');t=[];t.o=t.pop;t.u=t.push;for(j=0;e=i[j++];)+e==e?t.u(e*1):eval('s=t.o(),t.u(t.o()'+e+'s)');return t[0]}
function(a,b){b=[];a.replace(/\S+/g,function(c){b.push(+c==c?c:eval((a=b.pop(),b.pop())+c+a))});return b[0]}
That's more like it. Well done :)
Yay! @tobeytailor got it to just under tweet-size! Then @subzey cut it down/reimplemented it to 108 bytes! I'll be updating.
Save some bytes.
function(a,b){return(b=[])[a.replace(/\S+/g,function(c){b.push(+c==c?c:eval(b.pop(a=b.pop())+c+a))}),0]}
Great! I will update later. (Edit: done)
If 0 wasn't allowed as an operand, we could shorten it to
function(a,b){return(b=[])[a.replace(/\S+/g,function(c){b.push(+c||eval(b.pop(a=b.pop())+c+a))}),0]}
But it is...
Using the ideas outlined above, the eval-less version now is under 140 bytes too (138 bytes):
function(a,b){return(b=[])[a.replace(/\S+/g,function(c,d){b.push(+c==c?+c:(d=b.pop(a=b.pop()),c=='+'?d+a:c=='-'?d-a:c=='*'?d*a:d/a))}),0]}
Thanks everyone.
Save 2 bytes.
function(a,b){return(b=[])[a.replace(/\S+/g,function(c,d){b.push(+c==c?+c:{'+':(d=b.pop(a=b.pop()))+a,'-':d-a,'*':d*a,'/':d/a}[c])}),0]}
or this
function(a,b){return(b=[])[a.replace(/\S+/g,function(c,d){b.push(+c==c?+c:[(d=b.pop(a=b.pop()))+a,d-a,d*a,d/a]['+-*/'.indexOf(c)])}),0]}
I'm learning something in every comment. Great work, @tsaniel!
With ES6 you can
d variable to the top so you can ignore one (, )=> function you can also remove all return and make one liner by omitting {} that makes it return the first thing(a,b,d)=>(b=[])[a.replace(/\S+/g,c=>b.push(+c==c?+c:{'+':(d=b.pop(a=b.pop()))+a,'-':d-a,'*':d*a,'/':d/a}[c])),0]
Current size is 240 bytes. If we use eval, we can cut it down to 164 bytes:
function(i,s,t,j,e){i=i.split(' ');t=[];t.o=t.pop;t.u=t.push;for(j=0;j<i.length;j++){e=i[j];/[\d]+/.test(e)?t.u(e*1):eval('s=t.o(),t.u(t.o()'+e+'s)')};return t[0];}
I'll quote @140bytes on eval: "avoid it if you can, but sometimes ya gotta do what ya gotta do."
Is it possible to remove 100 bytes, or should we aim for the extra 24 bytes in the eval version?