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Regexp arity revisited

 
 
trans. (T. Onoma)
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      10-20-2004
Okay, I'm back to needing Regexp arity, and then some --I also need to know if
a particular subexpression if a zero-width positive lookahead. Why?

Have a look at this lovely interface:

class SplitToken < Token
def_attr :start_token, :end_token
def_attr :start_pattern, :end_pattern
def_attr :start_char, :end_char
def initialize( name, start_token, end_token, start_char=''..'',
end_char=''..'', opt=[] )
super( name, opt )
@start_token = start_token
@end_token = end_token
@start_char = start_char
@end_char = end_char
@start_pattern = /(#{start_char.first})(#{Regexp.escape(start_token) })
(#{'?=' if start_reuse?}#{start_char.last})/
@end_pattern = /(#{end_char.first})(#{Regexp.escape(end_token)})(# {'?='
if end_reuse?}#{end_char.last})/
end
# ...
end

class BlockToken < SplitToken
def initialize( name, start_pattern, opt=[] )
super( name, start_pattern, '', '\n\s*'..'', ''...'\n\ *\n' , opt |
[ :NEWLINE ] )
end
# ...
end

Notice the tricky way I use Ranges. #start_reuse? and #end_reuse? actually
just check @start_char.exclude_end? and @end_char.exclude_end? respectively.

I really don't want to do this. I'd rather just let the interface accept
Regexps directly, but then I would like to a) check for arity == 3 to make
sure they are valid and b) need to know if last subexpression is zero-width
lookahead.

I'll have to work around. But I think this represents the real use case --when
an interface accepts regexp and it wants to make sure they are valid.

T.


 
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