
On Oct 6, 2010, at 5:39 AM, Simon Marlow wrote:
A slightly different suggestion from Simon PJ and myself (we agreed on something syntax-related :-) is the following:
\case 1 -> f 2 -> g
where the two-token sequence '\ case' introduces a new optional layout context, the body of which is exactly the same as in a case expression. So you could also write
\case { 1 -> f; 2 -> g }
if you want. Guards are allowed of course.
* a bit more noisy than just \: I'm not sure what the ramifications of having \ introduce a layout context on its own would be, but I suspect there would be difficulties. Certainly some existing code would fail to parse, e.g.
(case e of [] -> \x -> x+1; (x:xs) -> \x -> x+2)
\ introducing a layout context is a no-go because, as in the example given, it breaks too much code. However, \case as described is somewhat less powerful. In particular, \ with a layout context lets us have multi-argument pattern matching, while both \case and "case of" give only single argument pattern matching. I don't know if the extra functionality is that important, but I don't see why we can't provide for it anyway, as in: \case (x:xs) n -> go xs; _ n -> n; Cheers, Sterl.