[Haskell-cafe] Foldable for BNFC generated tree

[Johan Jeuring]

Hi Deniz,

>> Deniz Dogan wrote:
>>>
>>> So, basically I'd like some sort of folding functionality for these
>>> data types, without having to hack the lexer/parser myself
>>> (parameterising the data types), because as I said they're being
>>> generated by BNFC.
>>
>> What exactly do you mean by folding functionality? Folding as in the
>> Foldable type class applies to containers, which your data type  
>> isn't.
>> Perhaps you're looking for generic programming?
>>
>> There are several good GP libraries out there:
>>
>> * EMGM: http://www.cs.uu.nl/wiki/GenericProgramming/EMGM
>> * Uniplate: http://community.haskell.org/~ndm/uniplate/
>> * SYB: http://www.cs.vu.nl/boilerplate/
>>
>> See also Neil Mitchell's blog for some examples:
>> http://neilmitchell.blogspot.com/2009/03/concise-generic-queries.html
>
> You're right, what I was asking for didn't make much sense... I was
> really looking for GP.

If I interpret your question correctly, you want a fold for a set of
mutually recursive datatypes without type parameters. This function is
available in the generic programming library multirec:

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/multirec

Kind reagrds,

Johan Jeuring