On 2006-08-18 at 17:30+0200 "John Hughes" wrote:
From: Jon Fairbairn
A reasonable choice (forestalling the objection that using List.map, listMap or mapList would be too distracting for students) would be
lmap:: (t -> t') -> [t] -> [t'] map:: Functor f => (t -> t') -> f t -> f t'
I'd prefer mapList to lmap, to be honest--at least the connection between the name and the type is clear. But remember, this would at a stroke make Haskell' incompatible with all existing Haskell textbooks.
so publishers should love it! ;-)
Even if publishers brought out new editions, even if we told students to buy them, there are many, many second hand books in circulation, and it would be years before one could rely on students having Haskell' books. All that time, students would write map instead of mapList because that's what the book says, and get stuck with incomprehensible error messages. Is it really worth an incompatible change in the library functions used by all beginners, just to rename fmap to map? It seems to me that the gain from a change is very small, and the cost considerable.
It depends over how long a time you amortise the cost. I've heard that when people complained about the problems of having tab significant in makefiles, no correction was made because there were about a dozen users. We're farther on than that, but still at a stage where the population of users is not that large, and the users are flexible. So I think we should be reasonably bold about these things. To reinforce what Aaron said, if a programme works now, it'll still work if map suddenly means fmap. Jón -- Jón Fairbairn Jon.Fairbairn at cl.cam.ac.uk