[Haskell-cafe] Point-free style in guards

Evan Laforge qdunkan at gmail.com
Tue Jul 22 13:33:54 EDT 2008

On Tue, Jul 22, 2008 at 10:27 AM, Neil Mitchell <ndmitchell at gmail.com> wrote:
> Hi
>> Why such a style doesn't work, so I must write ugly code like that:
>> outStanza a | (isMessage a) = outMessage a
>>              | (isPresence a) = outPresence a
>>             | (isIQ a) = outIQ a
> You can make it slightly prettier, since the brackets are not necessary:
> outStanza a | isMessage a = outMessage a
>             | isPresence a = outPresence a
>            | isIQ a = outIQ a

Also, if it really is in that format, maybe you can write something like:

switch v pairs = maybe (error "no match") ($v) (lookupWith ($v) pairs)

And then you can write the list point-free, though you don't get the
nice guard syntax.  I guess lookupWith must be one of my local
functions, but it's easy to write too.

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