On Thu, Mar 17, 2011 at 3:25 PM, Bas van Dijk <v.dijk.bas@gmail.com> wrote:

Hello,

I would like to propose making inits and tails less strict:

inits :: [a] -> [[a]]
-inits [] = [[]]
-inits (x:xs) = [[]] ++ map (x:) (inits xs)
+inits xs = [] : case xs of
+ [] -> []
+ x:xs -> map (x:) (inits xs)

tails :: [a] -> [[a]]
-tails [] = [[]]
-tails xxs@(_:xs) = xxs : tails xs
+tails xxs = xxs : case xxs of
+ [] -> []
+ _:xs -> tails xs

Having a lazier inits allows the elegant:
nats = map length (inits nats)
which loops for the current definition. This definition was due to John Tromp:
http://www.mail-archive.com/haskell@haskell.org/msg21044.html

Discussion deadline: 2 weeks.

Regards,

Bas

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