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Question

Regex to parse functions with arbitrary depth

Answer 1

A:

You might want to look at this link: http://www.xtremevbtalk.com/archive/index.php/t-177848.html

Matt Caldwell 2010-10-27 00:27:19

@Matt Caldwell - looked at the link but it doesn't resolve my issue. I'm not trying to use Excel to evaluate a function, I'm trying to breakdown larger functions in code. This should be possibly without loading Excel.

SFun28 2010-10-27 01:12:16

Answer 2

+1 A:

This is well within the capabilities of .NET regexes. Here's a working demo:

using System;
using System.Text.RegularExpressions;

namespace Test
{
  class Test
  {
    public static void Main()
    {
      Regex r = new Regex(@"
        (?<name>[a-z][a-z0-9]*\()
          (?<body>
            (?>
               \((?<DEPTH>)
             |
               \)(?<-DEPTH>)
             |
               [^()]+
            )*
            (?(DEPTH)(?!))
          )
        \)", RegexOptions.IgnoreCase | RegexOptions.IgnorePatternWhitespace);

      string formula = @"=Date(Year(A$5),Month(A$5),1)-(Weekday(Date(Year((A$5+1)),Month(A$5),1))-1)+{0;1;2;3;4;5}*7+{1,2,3,4,5,6,7}-1";

      foreach (Match m in r.Matches(formula))
      {
        Console.WriteLine("{0}\n", m.Value);
      }
    }
  }
}

output:

Date(Year(A$5),Month(A$5),1)

Weekday(Date(Year((A$5+1)),Month(A$5),1))

The main problem with your regex was that you were including the function name as part of the recursive match--for example:

Name1(...Name2(...)...)

Any open-paren that wasn't preceded by name was not counted, because it was matched by the final alternative, |.?), and that threw off the balance with the close-parens. That also meant that you couldn't match formulas like =MyFunc((1+1)), which you mentioned in the text but didn't include in the example. (I threw in an extra set of parens to demonstrate.)

EDIT: Here's the version with support for non-significant, quoted parens:

  Regex r = new Regex(@"
    (?<name>[a-z][a-z0-9]*\()
      (?<body>
        (?>
           \((?<DEPTH>)
         |
           \)(?<-DEPTH>)
         |
           ""[^""]+""
         |
           [^()""]+
        )*
        (?(DEPTH)(?!))
      )
    \)", RegexOptions.IgnoreCase | RegexOptions.IgnorePatternWhitespace);

Alan Moore 2010-10-27 03:00:01

@Alan Moore - Ah! Thanks! I would not have figured that out myself. This is the right solution. Thank you for believing me that this could be done with Regex =) Ok...I'll throw this out there purely as extra-credit/absolutely not needed/still grateful that you unblocked me: is there a way to ignore parens within quotes?

SFun28 2010-10-27 03:51:55

@Alan Moore - last comment submitted before complete. So the idea is that =Func("Hel(o") parses fine. I'm throwing this out there because I have a feeling that someone will be asking this very question in the future. For my purposes, I can guarantee that no strings will have unbalanced parens.

SFun28 2010-10-27 03:54:42

@SFun28: All you need to do is add another alternative to match complete, quoted sections, and then exclude quotes as well as parens in the final, *everything else* alternative: `(?>\\((?<DEPTH>)|\\)(?<-DEPTH>)|""[^""]+""|[^()""]+)*`

Alan Moore 2010-10-27 06:04:42

As such? @"(?<name>[a-z][a-z0-9]*\()(?<body>(?>\((?<DEPTH>)|\)(?<-DEPTH>)|""[^""]+""|[^()""]+)*(?(DEPTH)(?!)))\)"

SFun28 2010-10-27 14:08:02

That seems to break some tests (man, i can't press enter for newline in this textbox)

SFun28 2010-10-27 14:08:53

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Regex to parse functions with arbitrary depth

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