inits

[Josef Svenningsson]

On 4/9/06, Aaron Denney <wnoise at ofb.net> wrote:
> inits xs = zipWith take [0..] $ map (const xs) (undefined:xs)
>
Nicest version so far!

> (I still think letting head $ inits undefined be [] rather than
> undefined is better than the current def.)
>
Yes, from a termination point of view it surely seems better with the
lazy version. But I believe that this is the wrong way of seeing it.
These termination issues are hardly any problem in every-day
programming. But what few people here seem to realize is that a change
in the strictness of a function will change the space behaviour of a
program. I use that as a rule of thumb when inspecting Haskell code:
whenever the strictness changes that will lead to a change in memory
consumption. So changing inits to a lazier version will  not affect a
lot of program termination-wise but it will have effects on the space
consumption. Whether these effects will be good of bad depends on the
program, but the fact remains, there will be a change. I think this is
unwelcome and that's why I think that the strictness properties of the
Prelude functions should be preserved.

Cheers,

/Josef