Modifying a for loop in a string

Question

I have string it contains some code. I want to make some changes on it. There is a for loop I want to modify with js. The loop:

"for i in 0..10 loop"

I want it to be:

"for (var i=0; i<10; i++)"

It sounds me very complicated. What should be the easiest approach?

Not really complicated, assuming the pattern is fixed - for [name of variable] in [start index] .. [end index] loop - bolded are the fixed words. If this is the case just split by space and take the stuff you need. — user447356
– user447356, Commented Dec 29, 2011 at 8:00
Wouldn't 0..10 need i<=10 in JS? (Or am I misinterpreting the starting language?) — nnnnnn
– nnnnnn, Commented Dec 29, 2011 at 8:27
That's how I read it too, and how my initial answer was written, but to each his own I guess. — Interrobang
– Interrobang, Commented Dec 29, 2011 at 8:37

user447356 · Accepted Answer · 2011-12-29 08:13:42Z

Based on my comment here is simple implementation:

var before = "for i in 0..10 loop";
var after = Translate(before);

function Translate(command) {
    var tokens = command.split(" ");
    if (tokens.length != 5)
        return "ERROR: invalid command (wrong number of tokens)";
    if (tokens[0] != "for" || tokens[2] != "in" || tokens[4] != "loop")
        return "ERROR: invalid command (syntax error)";
    var indices = tokens[3].split("..");
    if (indices.length != 2)
        return "ERROR: invalid command (invalid indices format)";
    var startIndex = parseInt(indices[0], 10);
    var endIndex = parseInt(indices[1], 10);
    if (isNaN(startIndex) || isNaN(endIndex))
        return "ERROR: invalid command (illegal indices)";
    var varName = tokens[1];
    return "for (var " + varName + "=" + startIndex + "; " + varName + "<" + endIndex + "; " + varName + "++)";
}

Live test case.

It's not perfect, for example you can further check the variable name is legal i.e. start with English letter, not a reserved word etc.

Interrobang · Accepted Answer · 2011-12-29 08:14:54Z

2

You can use regex matching to pull out the parts you are interested in.

var string_to_match = 'for i in 0..10 loop',
    re = /for ([A-z]*) in (\d*)\.\.(\d*) loop/,
    data = re.exec(string_to_match);

// data contains:
// ["for i in 0..10 loop", "i", "0", "10"]

for(i = data[2]; i < data[3]; i++) {
    console.log(i);
}

answered Dec 29, 2011 at 8:14

Interrobang

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Comments

Purag · Accepted Answer · 2011-12-29 08:16:04Z

1

Here's a way to do it, but probably not the best:

var str = "for i in 0..10 loop",
    str = str.replace("i in ", "(var i="),
    str = str.replace("..", "; i<"),
    str = str.replace(" loop", "; i++)");
console.log(str);

Example.

answered Dec 29, 2011 at 8:16

Purag

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Comments

Francois · Accepted Answer · 2011-12-29 08:50:44Z

0

You can try to match this regular expression ^for (.+) in (\d+)\.\.(\d+) loop$ and replace with for (var \1=\2; \1 < \3; \1++).

Try it on http://www.solmetra.com/scripts/regex/ for example...

answered Dec 29, 2011 at 8:50

Francois

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