Proposal: making inits and tails less strict

[Bas van Dijk]

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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