inits is too strict

[Donald Bruce Stewart]

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