[Haskell-cafe] Re: Lambda-case / lambda-if
Dean Herington
heringtonlacey at mindspring.com
Wed Oct 6 19:45:42 EDT 2010
At 4:43 PM -0400 10/6/10, Sterling Clover wrote:
>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._______________________________________________
I would also very much like to have multi-argument pattern matching, but in
\case a b -> ...
...
it sure suggests to me that `a` should be applied to `b` before casing.
Dean
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