Twan, The 0-ary version you proposed actually works even nicer with \of. foo'' = case () of () | quux -> ... | quaffle -> ... | otherwise -> ... Starting from the above legal haskell multi-way if, we can, switch to foo' = case of | quux -> ... | quaffle -> ... | otherwise -> ... using the 0-ary form of case as a multi-way if, but since the motivation was to allow the min \of, we get the very terse foo = \of | quux -> ... | quaffle -> ... | otherwise -> ... and you get wind up with layout starting on the |'s so they line up per-force. baz = \of Just x -> Just (x + 1) Nothing -> Nothing avoids an ugly temporary for baz' mx = case mx of Just x -> Just (x + 1) Nothing -> Nothing and in the multi-argument case, the resulting syntax is actually comparably noisy to the direct declaration syntax. One , as opposed to two pairs of parentheses in bar''' below. bar = \of Just x, Just y -> Just (x + y) _ , _ -> Nothing bar' mx my = case mx, my of Just x, Just y -> Just (x + y) _ , _ -> Nothing bar'' mx my = case (# mx, my #) of (# Just x, Just y #) -> Just (x + y) (# _ , _ #) -> Nothing bar''' (Just x) (Just y) = Just (x + y) bar''' _ _ = Nothing -Edward On Fri, Jul 6, 2012 at 3:12 AM, Edward Kmett <ekmett@gmail.com> wrote:
Oh, neat. I guess it does. :) I'll hack that into my grammar when I get into work tomorrow.
My main point with that observation is it cleanly allows for multiple argument \of without breaking the intuition you get from how of already works/looks or requiring you to refactor subsequent lines, to cram parens or other odd bits of syntax in, but still lets the multi-argument crowd have a way to make multi-argument lambdas with all of the expected appropriate backtracking, if they want them. I definitely prefer \of to \case given its almost shocking brevity and the fact that the fact that it introduces a layout rule doesn't change any of the rules for when layout is introduced.
On Jul 5, 2012, at 5:33 PM, Twan van Laarhoven <twanvl@gmail.com> wrote:
On 2012-07-05 23:04, Edward Kmett wrote:
A similar generalization can be applied to the expression between case and of to permit a , separated list of expressions so this becomes applicable to the usual case construct. A naked unparenthesized , is illegal there currently as well. That would effectively be constructing then matching on an unboxed tuple without the (#, #) noise, but that can be viewed as a separate proposal' then the above is just the elision of the case component of:
Should that also generalize to nullarry 'case of'? As in
foo = case of | guard1 -> bar | guard2 -> baz
instead of
foo = case () of () | guard1 -> bar | guard2 -> baz
I realize this is getting off-topic, and has become orthogonal to the single argument λcase proposal.
Twan
_______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users