On Friday 01 April 2011 09:00:56, oleg@okmij.org wrote:
Daniel Fischer wrote:
If you have a strict function, you may evaluate its argument eagerly without changing the result^1, while eager evaluation of a non-strict function's argument may produce _|_ where deferred evaluation wouldn't.
Sadly, that is quite untrue. Strictness is observable, already in Haskell98. That distressing result has nothing to do with imprecise exceptions, seq, non-termination, lack of resources, or the use of unsafe features. Plainly, just by changing the strictness of a function one may cause the program to print different results, such as "strict" or "non-strict" in the code below.
John Meacham said it's not Haskell98, I can't be bothered to check the H98 report now, since that's a minor point anyway. So, mea culpa, I didn't consider catch at all, only thought of non-IO code and considered all _|_s equal. I should have made these restrictions explicit, but I wasn't even consciously aware of them.