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.