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Re: regular expressions

• To: David Tolpin <dvd@d...>
• Subject: Re: regular expressions
• From: Bob Foster <bob@o...>
• Date: Thu, 29 Jan 2004 18:35:57 -0600
• Cc: xml-dev@l...
• In-reply-to: <200401292002.i0TK2kHX080757@a...>
• References: <200401292002.i0TK2kHX080757@a...>
• User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.5) Gecko/20031007

 > Why isn't it done?

Good question. It should be. Of course, the notation suggests to most 
compsci people that recursion will be permitted, i.e., that this is a 
context-free instead of regular grammar, and that's probably not what 
you intended.

Bob Foster
http://xmlbuddy.com/

David Tolpin wrote:
> Some schema languages use string regular expressions to check lexical space of 
> attributes and character data. The regex strings often become uncomprehensible,
> such as
> 
> (([a-zA-Z][0-9a-zA-Z+\-\.]*:)?/{0,2}[0-9a-zA-Z;/?:@&=+$\.\-_!~*'()%]+)?(#[0-9a-zA-Z;/?:@&=+$\.\-_!~*'()%]+)?
> 
> for any URI. 
> 
> Providing a structured syntax, similar to that for XML, would help reading and debugging
> them, for example,
> 
>     s-pattern="""
>       comment = "\(([^\(\)\\]|\\.)*\)"
>       atom = "[a-zA-Z0-9!#$%&'*+\-/=?\^_`{|}~]+"
>       atoms = atom "(\." atom ")*"
>       person = "\"([^\"\\]|\\.)*\""
>       location = "\[([^\[\]\\]|\\.)*\]"
>       local-part = "(" atoms "|" person ")"
>       domain = "(" atoms "|" location ")"
>       start = "(" comment " )?" local-part "@" domain "( " comment ")?"
>     """
> 
> instead of 
> 
>     pattern=
>       "(\(([^\(\)\\]|\\.)*\) )?"
>     ~ """([a-zA-Z0-9!#$%&'*+\-/=?\^_`{|}~]+(\.[a-zA-Z0-9!#$%&'*+\-/=?\^_`{|}~]+)*|"([^"\\]|\\.)*")"""
>     ~ "@" 
>     ~ "([a-zA-Z0-9!#$%&'*+\-/=?\^_`{|}~]+(\.[a-zA-Z0-9!#$%&'*+\-/=?\^_`{|}~]+)*|\[([^\[\]\\]|\\.)*\])"
>     ~ "( \(([^\(\)\\]|\\.)*\))?"
> 
> Why isn't it done?
> 
> David
> 
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