Comments on: Balanced parenthesis

By: A PROGRAMMING JOB INTERVIEW CHALLENGE #14 - 2D GEOMETRY | Dev102.com

A PROGRAMMING JOB INTERVIEW CHALLENGE #14 - 2D GEOMETRY | Dev102.com — Tue, 05 Aug 2008 09:59:27 +0000

[...] http://www.fsharp.it/2008/07/22/balanced-parenthesis/ by Claudio Cherubino. [...]

By: Validating use of Parenthesis • OJ’s rants

Validating use of Parenthesis • OJ’s rants — Wed, 23 Jul 2008 23:10:21 +0000

[...] surprisingly similar to this solution over at Fsharp.it. It is different in that it allows non-bracket characters to be entered into the [...]

By: Mat/Tia

Mat/Tia — Wed, 23 Jul 2008 08:40:41 +0000

Just to be theoretical , remember that “pure” regular expressions (I mean: something that can be translated into finite automatons) aren’t expressive enough to solve the balanced-parenthesis problem.
It is also true that most regular expressions implementations are expanded so to fit also this as a special case.

By: claudio

claudio — Wed, 23 Jul 2008 06:51:22 +0000

The trick to return true is hidden in this line:

| [] -> stack = List.Empty

remember that = is the comparison operator, as the == operator in other languages.

This line says: when char_array is empty, if the stack is empty return true, otherwise return false.

Actually, I didn’t use the is_closing function and I assumed that every character that is not an opening bracket will be a closing one.

To be safe, I’d add another line to the first pattern matching and check if the examined character is a closing parenthesis.
Any other character should warn the user that the input string is not valid.

By: Ben

Ben — Wed, 23 Jul 2008 06:34:59 +0000

When does this return true?
And when do you use is_closing?