On Sun, 2009-01-18 at 12:02 +0100, Marcus D. Gabriel wrote:
Brent Yorgey wrote:
P2. There should be no information loss, that is, keep the delimiters, keep the separators, keep the parts of the original list xs that satisfy a predicate p, do not lose information about the beginning and the end of the list relative to the first and last elements of the list respectively. The user of the function decides what to discard.
P3. A split list should be unsplittable so as to recover the original list xs. (I made up the word unsplittable.) (P2 implies P3, but let us state this anyway.)
I'm not sure I agree with this.
Thanks for stating this. Dropping P3 would change my thinking about this topic, that is, if we drop P3, then I would prefer that no splitter functions are added to Data.List and that it is left as is.
The problem is that much (most?) of the time, people looking for a split function want to discard delimiters; for example, if you have a string like "foo;bar;baz" and you want to split it into ["foo","bar","baz"].
I agree with this comment when thinking about strings and what I would do most of the time and from a pragmatic point of view.
Indeed, the existing Data.List.words is certainly lossy and deliberately so. It's also useful and widely used. On the other hand it is a widely held view that Data.List.lines should not be lossy, ie that Data.List.unlines . Data.List.lines should be the identity. In the current implementation of lines . unlines it is not the case because of the way it handles a trailing newline. Duncan