inits

[Chris Kuklewicz]

Aaron Denney wrote:
> On 2006-04-08, Nils Anders Danielsson <nad at cs.chalmers.se> wrote:
>> On Fri, 07 Apr 2006, "Spencer Janssen" <spencerjanssen at gmail.com> wrote:
>>
>>>> inits xs = [] : (zipWith take [1..] $ map (const xs) xs)
>>> As this version performs much better and will work as a drop in
>>> replacement, I suggest that it be included in the hierarchical
>>> libraries.
>> It is not a drop in replacement. The original inits is strict, this
>> one isn't.
>>
>> The specification of inits (from the Haskell 98 report):
>>
>>   inits                   :: [a] -> [[a]]
>>   inits []                =  [[]]
>>   inits (x:xs)            =  [[]] ++ map (x:) (inits xs)
> 
> Is that a property many programs depend on?  I'd actually call that a
> bug of the original.
> 

It may break some things:

head (Data.List.inits undefined) is an error

head (New.Spiffy.inits undefined) is []

-- 
Chris