On Thursday, January 27, 2000 2:08 PM, Frank A. Christoph
[SMTP:[EMAIL PROTECTED]] wrote:
>> My preference is still (B). (A) is not *very* bad, but should really
>> replicate (-7) "foo" be []?
>
>I could say: Sure, why not? replicate suffers from the same domain problem
>as take/drop.
This was not the point of introducing replicate to the discussion.
The Prelude says, in a comment,
-- replicate n x is a list of length n with x the value of every element
and then defines replicate in terms of take.
replicate :: Int -> a -> [a]
replicate n x = take n (repeat x)
There is a clear assumption on the part of the Prelude authors that take behaves in a
particular
way, corresponding to the law
length (take n xs ) === n
but it doesn't. So even the authors of the Prelude got caught by take's inconsistency.
While I dislike functions with a simple, obvious intended semantics being extended in
non-obvious,
non-simple ways, because it creates just this kind of error, I understand that many
people are less concerned
about it. I can live with any of the proposed definitions, but do suggest that
incorrect statements are corrected.
So, if negative values are to be allowed in take, the comment re replicate should say,
-- if n >=0 replicate n x is a list of length n with x the value of every element
Or, if negative values are *not* to be allowed in take, then fix the present code so
that they are
not allowed for any list, including [].
--brian
