On Monday 04 September 2006 16:21, Audrey Tang wrote: > 2006/9/4, Ph. Marek <[EMAIL PROTECTED]>: > > Excuse me for getting into this thread with only minor knowledge about > > perl6, but will there be MMD based on the *value* of parameters? Like > > Haskell has. > > Why, yes, see the various Unpacking sections in S06, as well as "where" > type constraints. We're st^H^Hadapting as much as we can. :-) Hello Audrey!
I now had a look at http://dev.perl.org/perl6/doc/design/syn/S06.html but didn't find what I meant. Sorry if I'm just dumb and don't understand you (or S06); I'll try to explain what I mean. In Haskell you can eg. write: SomeThing :: Int -> Int -> Int SomeThing a b | a = 4 : b+2 | b = 3 : a+1 | otherwise : a*b or AnotherThing :: Int -> Int -> Int AnotherThing 4 b = b+2 AnotherThing b 3 = a+1 AnotherThing a b = a*b In Perl5 this looks like sub SomeThing { my($a, $b)[EMAIL PROTECTED]; return b+2 if ($a == 4); return a+1 if ($b == 3); return a*b; } Which is a bit wrong IMO, because the condition should be first. But sub SomeThing { my($a, $b)[EMAIL PROTECTED]; if ($a == 4) { return b+2 } if ($b == 3) { return a+1 } return a*b; } is a bit of a hazzle with the {} and repeated if()s. What I am asking is whether there will be some multimethod dispatch depending on the *value*, not the *type*, of parameters. Perl6 could possibly do something with "given"; but matching on multiple variables seems to be verbose, too. I'm looking for something in the way of sub SomeThing(Num $a, Num $b) where $a==4 is $b+2; sub SomeThing(Num $a, Num $b) where $b==3 is $a+1; sub SomeThing(Num $a, Num $b) { return $a * $b } but without specifying the signature multiple times (or maybe we should, since it's MMD). Now sub SomeThing(Num $a, Num $b) { if $a==4 { return $b+2; } if $b==3 { return $a+1; } return $a * $b; } would almost do what I want, but I don't know if the compiler would optimize that in the way it could for direct MMD depending on types. Regards, Phil
