[Haskell-cafe] Re: type class question
jules at jellybean.co.uk
Mon Dec 10 06:34:32 EST 2007
Try again without missing out the list...
Peter Padawitz wrote:
> Jules Bean wrote:
>> Incidentally, I question why the "compFoo" are methods. Why not just
make them polymorphic functions? They don't look like you expect
instances to change them. The code continues to compile if I make them
functions and amend their signatures as required.
> I put compFoo into the class for the same reason why /= is part of
the class Eq: both functions are unique as soon as the others have been
I believe you misunderstand the reason.
/= is part of Eq in case a particular instance has a particularly
efficient way to implement /=, rather than using not and (==).
"Being unique as soon as the others are implemented" is not a reason not
to make it a method.
compBlock :: (Java block command intE boolE) => Block -> block
compBlock = block_ . map compCommand
still retains that property.
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