Re: inits

8 Apr 2006


      On 2006-04-08, Nils Anders Danielsson  wrote:
...
On Fri, 07 Apr 2006, "Spencer Janssen"  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.

-- 
Aaron Denney
-><-