apfelmus:
Hello,
inits [] = [[]] inits (x:xs) = [[]] ++ map (x:) (inits xs)
as specified in Data.List has a "semantic bug", namely it's too strict:
inits (1:_|_) = []:_|_
as opposed to the expected
inits (1:_|_) = []:[1]:_|_
A correct version would be
inits xs = []:case xs of [] -> [] (x:xs) -> map (x:) (inits xs)
The Haskell report specifies how inits has to behave, so this is a problem in the report, not in a concrete implementation. Where can I report a bug report for the report? ;)
Regards, apfelmus
Well, right here. There are other strictness issues either differing from the spec, or not clearly defined (foldl', for example). A useful tool for checking these is the StrictCheck/ChasingBottoms library, QuickCheck for partial values, by the way. -- Don