[Haskell-cafe] Point-free style in guards

Neil Mitchell ndmitchell at gmail.com
Tue Jul 22 13:27:07 EDT 2008


> 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

Although I suspect that outMessage crashes if isMessage returns False?
And perhaps outMessage is written as outMessage (Message a b) = ...

In which case, I'd write:

outStanza (Message a b) = ...

And then the code no longer looks ugly, uses pattern matching nicely,
requires no "is..." functions and won't crash if things like
outMessage are called incorrectly.

[Note, everything beyond the no need for brackets is a bit of a guess,
just possible ideas to think about]



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