john.tromp:

The standard definition of inits:

inits [] = [[]] inits (x:xs) = [[]] ++ map (x:) (inits xs)

is unnecessarily strict, evaluating its argument before yielding the initial [] of the result. An improved version is:

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

This allows one to define for instance nats = map length (inits nats) which loops for the standard definition.

Can you forward this to the libraries@haskell.org list, and file a proposal to replace the current definition? http://haskell.org/haskellwiki/Library_submissions We noticed this while implementing lazy bytestrings, which had a similar issue, and fixing it is cheap enough. -- Don