On 16 aug 2007, at 13.46, Bertram Felgenhauer wrote:
Duncan Coutts wrote:
On Wed, 2007-08-15 at 11:06 -0700, Stefan O'Rear wrote:
foo = getSomethingCPS $ \ arg ->
moreStuff
is now a syntax error (\ { varid -> } matches no productions).
I'm not sure I follow.
The patterns would have to match up in a column, so
foo = getSomethingCPS $ \ arg ->
moreStuff
should be fine, to add another alternative it'd have to be:
foo = getSomethingCPS $ \ Pat1 ->
moreStuff
Pat2 ->
evenMoreStuff
I don't like this - it's not in the spirit of the existing layout
rule at all. You should have to indent 'moreStuff' deeper than
Pat1 I think;
foo = getSomethingCPS $ \ Pat1 ->
moreStuff
Pat2 ->
evenMoreStuff
would be (visually) ok. But then Stefan's point is valid.
So there should be two productions, I think, one for non-case
lambdas and one for case-lambdas, like this:
non-case-lambda:
'\' apat+ '->' expr
case-lambda:
'\' '{' ( apat+ '->' expr ';' )* '}'
Unfortunately this naive approach would add another point of
arbitrarily large look-ahead to the grammar. The easiest way to
resolve this is to add some keyword before or after '\',
bringing is back to the previous proposals.
I like both
\of x y z -> ...
a b c -> ...
and
case \ of x y z -> ...
a b c -> ...
(I'd add the space here, viewing \ as a pseudo-expression)
In the spirit of the \\ proposal, while \\ itself is an operator,
\ \ x y z -> ...
a b c -> ...
is still available as a syntax, but may be confusing.
.\ x y z -> ...
a b c -> ...
or just require unicode \lambda ;)
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