[Haskell-cafe] Re: Type question in instance of a class
lemming at henning-thielemann.de
Sat Nov 22 16:36:28 EST 2008
On Sat, 22 Nov 2008, Janis Voigtlaender wrote:
> Definitely. And that surfaces even in quite innocently looking programs
> and statements about them. The introductory example of the following
> technical report may be amusing in that respect:
In example 1, I don't see on the one hand, why 'takeWhile (null.tail)'
could fail with "tail: empty list", since all lists in '[[i] | i <-
[1..(div 1 0)]]' are non-empty (namely singletons). On the other hand,
aren't those imprecise error problems not just proofs that mixing up
errors and exceptions (here treating errors as exceptions) is a bad thing?
'error' is only a candy version of 'undefined' for simplifying debugging.
If all 'error's are replaced by 'undefined' (plain bottom) then 'takeWhile
p (map h l)' and 'map h (takeWhile (p.h) l)' behave also visually
identical, don't they?
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