On 2006-10-27 at 17:56+0200 "Josef Svenningsson" wrote:
My argument for intercalate builds on the fact that intersperse seems to be the wrong abstraction. Recall that I supplied some evidence that intersperse is only used together with concat: http://www.google.com/codesearch?q=file%3A%5C.hs+intersperse&btnG=Search+Code
Mostly, not only.
For me this suggests that intersperse is the wrong abstraction. The right one is intercalate.
I don't agree with the methodology... Firstly, while extant code tells you how things have been used, it doesn't tell you how they /should/ be used. Second, I suspect that the majority of current Haskell code was written by novices -- I don't mean anyone any disrespect, it's just that it takes quite a long time to become an expert, the number of new novices has been increasing rapidly and the people who have known Haskell long enough to be experts probably nolonger write so much code: they get their students to do it :-). [How many of the cases you found should have been foldr (.) id etc?]
I know that many people will argue that intersperse is somehow more primitive or more natural than intercalate.
I don't know about natural. Looking back at the 25 year old Ponder list_ops library, I find that I defined join_with filler l1 [] = l1 join_with filler l1 l2 = l1 ++ filler ++ l2 and then flatten_with filler = foldr (join_with filler) [] which is another way of writing intercalate.
As for being more primitive, that's not true. Both functions are interdefinable.
Right. So your motive is more complicated than it appeared to me. I missed that first time round, sorry. The problem we have is that intersperse x == intercalate [x] . map (:[]) and intercalate x = concat . intersperse x While it seems easier to me to work out the second than the first, I don't know if that is simply due to habituation. I can add that the second /looks/ simpler. So I /suspect/ (unprovably) that were intercalate the preferred form, people would write intersperse in several different ways, in contrast to the present state of affairs where “concat . intersperse splod” seems already to have become idiomatic. What would convince me of your case would be someone saying that intercalate is the <oojit> of the <weeble> category while intersperse enjoys no such property... ... or maybe I was right back then, and the natural primitive is something like join_with -- an operation to use with foldr? -- Jón Fairbairn Jon.Fairbairn at cl.cam.ac.uk