pugs-comm...@feather.perl6.nl wrote:
> Author: masak
> Date: 2009-03-14 13:34:42 +0100 (Sat, 14 Mar 2009)
> New Revision: 25821
>
> Modified:
> docs/Perl6/Spec/S12-objects.pod
> Log:
> specced syntactic 'where' sugar in param lists
>
> Modified: docs/Perl6/Spec/S12-objects.pod
> ===================================================================
> --- docs/Perl6/Spec/S12-objects.pod 2009-03-13 15:44:50 UTC (rev 25820)
> +++ docs/Perl6/Spec/S12-objects.pod 2009-03-14 12:34:42 UTC (rev 25821)
> @@ -12,9 +12,9 @@
>
> Maintainer: Larry Wall <la...@wall.org>
> Date: 27 Oct 2004
> - Last Modified: 12 Mar 2009
> + Last Modified: 14 Mar 2009
> Number: 12
> - Version: 76
> + Version: 77
>
> =head1 Overview
>
> @@ -1305,6 +1305,18 @@
> since all the type constraints in a signature parameter are just
> anded together anyway.
>
> +You can leave out the block when matching against a literal value of some
> +kind:
> +
> + multi sub fib ($n where 0|1) { return $n }
> + multi sub fib (Int $n) { return fib($n-1) + fib($n-2) }
> +
> +In fact, you can leave out the 'where' declaration altogether:
> +
> + multi sub fib (0) { return 0 }
> + multi sub fib (1) { return 1 }
> + multi sub fib (Int $n) { return fib($n-1) + fib($n-2) }
As much as I like this new syntax, it's not as useful as it looks.
multi sub fib (0) desugars to (Any $ where 0), which is just a type
constraint in terms of multi dispatch. Which (Int $n) is also, so you
actually get an "ambiguous dispatch" error in your example.
Any thoughts on how that could be improved in a dwimmy way?
Cheers,
Moritz
