[Haskell-cafe] whine and solution about programmers not
daniel.is.fischer at web.de
Tue Jun 29 06:28:08 EDT 2010
On Tuesday 29 June 2010 11:46:47, Ketil Malde wrote:
> An important point of a powerful type system is to model your program so
> that only sensible code is legal.
That would be an awesomely powerful type system :)
> This makes me wonder why deleteBy is
> defined so loosely, instead of e.g.
> deleteBy :: (a -> Bool) -> [a] -> [a]
That would've been the (a) safer choice.
> I don't think there would be any doubt what 'deleteBy (<= 5) [1..10]'
> would do.
Well, if you don't know about filter, you could think it deletes all
elements satisfying the predicate, but apart from that, it's clear.
> And I just don't see what the requirement for an equivalence
> relation buys you.
For the type deleteBy has, predictability. Currently, you can't know
whether deleteBy pred x tests pred x y or pred y x without looking at the
source. For a symmetric relation, you needn't care.
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