On 11/19/2011 12:03 AM, Johan Tibell wrote:
Hi all,
[--snip--] Let me just preface this by saying that I'm definitely no expert on laziness/strictness in Haskell-land. Having followed the mailing lists for a few years, I definitely agree that this area is something which desperately needs attention from a practical point of view. (It seems there's a Monad.State.Strict thread every few months, etc.) So, FWIW:
More than one person said the distinction between (1) and (2) isn't clear
Does it really matter? AFAICT, the most important thing is that the use of the API doesn't lead to surprising behavior, aka. the principle of least astonishment (POLA). [--snip--]
Without the extra strictness there are degenerate cases that can catch people off guard. For example,
insertWith (\ old new -> if old == maxValue then old else new + 1) k v m
is lazy in 'v' because there's a rare case (old == maxValue) where 'new' isn't evaluated.
For me, this behavior would really violate the POLA. If I'm passing something to an API which "is strict" (as indicated by Data.Map.Strict), then I'd certainly expect everything I pass in to be evaluated. [--snip--] Are there any specific and serious disadvantes to including (1)? It might be useful to have a concise list for reference. (Sorry, I didn't follow the other thread closely.) -- Bardur Arantsson