Re: [SimpleParse] Graceful failure ?

[Mike C. F. <mcf...@ro...>]

H. T. Hind wrote:
...

>>column_specs := '<s>',ws,('<c>'?,ws)+,'\n'
>>    
>>
...

>Is there another way to define the above that avoids the loop ?
>We might not be able to anticipate all the data that we might
>encounter, hence it is essential to have the ability to fail with
>an error such that a human can intervene and fix the data. 
>  
>
This doesn't have anything to do with the data, the grammar itself is 
saying "if you match nothing here, go ahead and try to match it again".  
That is; to say the *exact* same thing with an engine such as 
mxTextTools, you can't spell it without defining a recursion, however, 
you probably don't want to anyway:
   
    column_specs := '<s>',ws,('<c>',ws)*,'\n'

is probably what you are looking for.  That is, to match the group 
within the brackets, you *must* find at least one '<c>', and optionally 
some whitespace, but if you don't find that, ignore the whole group, 
while allowing for repetition of the group.

>>It's possible to catch it, yes, but it would require some considerable 
>>work to modify the engine to be able to support the feature.
>>
>>    
>>
>
>Would you recommend then something like PLY ?
>  
>

If you feel like it would meet your needs.  You haven't yet outlined 
what you're actually trying to parse that would be a problem for 
SimpleParse (given a proper grammar).  Other parser-generators may use 
Earley or similar parsing mechanisms, which are more general than 
SimpleParse, but your parsing task here doesn't seem particularly to 
require such generality.

Anyway, good luck,
Mike

 
_______________________________________
  Mike C. Fletcher
  Designer, VR Plumber, Coder
  http://members.rogers.com/mcfletch/