Format text with javascript from right to left using regular expressions

Question

I have specific built in functions where admins can execute through a website. For simplicity let's pretend there are only 2 functions which are:

1) func1 "requires 2 paramters"

2) func2 "requires 3 paramters"

so I have a textbox where users can enter stuff like: I use ';' to separate the parameters

func1 x; y;  //  func1(x,y) is more understandable. func1 takes two parameters

or

func2 1; 2+2; 4;  // note that func2 takes 3 parameters...

or even more complicated nested functions such as;

func2  x; func1 a; b; ; z ; // for example in this example 1st parameter  = x
                                                           2nd parameter = func1 a; b; // note this is a function
                                                           3rd parameter = z

with the help of jquery I can take advantage of it's intellecence/autocomplete functions to make sure I type the name of the functions correctly.

now here is where I am stuck

I will like to inform to the user if he is missing to pass parameters on each function.

for example if the user types:

  func2 x; y;

then I will like to inform him that func2 is missing a parameter.

I know that will be eassy the problem is if the user types something like:

 func2  x; func1 a; b; ; z ;

I have managed to solve this with c#. It is very eassy. the way I do it is by start looking for functions from right to left. so if I do so the first function that I will find is func1 right? then I will more right until I find two ;'s if I replace that then I will have: func2 x; <temp> ; z ; note I replaced func1 a; b; with then I can continue doing the same thing and I will then find func2 and select until the 3rd ;'s

the problem is that if I create a regular expresion I don't know how to start looking from right to left. If I were to start looking from left to right like it is the default then func2 will have it's first paramter = x, it's second paramter = func1 a, and it's 3rd parameter = b. and that is not the case. If on the other hand I start doing the same thing from right to left everything works out.

Ivan Castellanos · Accepted Answer · 2012-01-11 05:26:34Z

1

So the hard part is going right to left? Use split regex and then reverse

var valid_functions = ["func1","func2"]
var valid_params = [4,1]

var f_regex = new RegExp("\\b("+valid_functions.join("|")+")\\b");
var f_data = "func2  x; func1 a; b; ; z ;".split(f_regex).reverse();
for(var i=0;i<f_data.length;i+=2){   
    if(f_data[i] === ""){continue}  
    var f_name = f_data[i+1],
        f_params = f_data[i];    
    var pos = valid_functions.indexOf(f_name);
    if( f_params.split(";").length-1 !== valid_params[pos]){
        alert("Wrong number of arguments for " + f_name)
    }
}

Example of function with incorrect number of parameters: http://jsfiddle.net/tHcYM/1/

edited Jan 11, 2012 at 5:26

answered Jan 11, 2012 at 4:47

Ivan Castellanos

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2 Comments

Tono Nam Over a year ago

what browser did you used. when I type func2 x; func1 a b; ; z ; it does not say that the function is invalid. recall that func1 requires 2 parameters and func2 requires 3. Thanks for the help!

Ivan Castellanos Over a year ago

Fixed, in the "valid functions" you write the names of the valid functions; and in valid params the number of correct arguments for each one (In this example, func1 accepts 4 params). If you want this code to work in old browsers you have to implement Array.indexOf, copy it from here: soledadpenades.com/2007/05/17/arrayindexof-in-internet-explorer

aaronblohowiak · Accepted Answer · 2012-01-11 04:41:04Z

0

You cannot use regular expressions for this in a reliable way. Regular expressions are regular languages. You have introduced context-dependence, which means that your language is no longer "regular" in the strictest sense.

You should be able to port your c# code to javascript. What string manipulation functions are "missing" from JS that you use in c# that made you think you should use regex in js?

answered Jan 11, 2012 at 4:41

aaronblohowiak

641 bronze badge

2 Comments

Tono Nam Over a year ago

I know I can use the c# code. But I don't want to make an ajax request every time the user types a character. It will be nice if I could validate it with javascript on the client side instead of having the server do it. There are not to many functions and I think it should be not to complicated to implement...

aaronblohowiak Over a year ago

Right, I'm not suggesting that you use the c# code directly, but I am suggesting that you don't need to use regexes to do this task. Why dont you implement the same algorithm in js as you used in c# ?

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