Tom Pledger <[EMAIL PROTECTED]> writes
> [..]
> lazinessTest = head $ fst $ partition (==1) [0..]
> lazinessTest' = head $ fst $ partition' (==1) [0..]
>
> Main> lazinessTest
>
> (35927 reductions, 63879 cells)
> ERROR: Control stack overflow
> Main> lazinessTest'
> 1
> (36 reductions, 73 cells)
>
> Any ideas about why this happens, please?
By the way, the List.partition definition
\p xs -> (filter p xs, filter (not .p) xs)
is not it the simplest and the best implementation?
It looks like the existing implementations do not use it.
Correctness question
--------------------
The implementations optimize the standard functions in various ways.
But what about correctness, what the standard says?
For example, the definition from the List.partition _document_
implies that
head $ fst $ partition (==1) [0..] = 1
And some implementations get into infinite loop at this
(may this loop be called `undefined', is it equivalent ?).
What freedom the language and library description allows with this
respect?
------------------
Sergey Mechveliani
[EMAIL PROTECTED]
