On Mon, 2007-10-01 at 22:34 -0700, Erick Tryzelaar wrote:
> On 10/1/07, skaller <[EMAIL PROTECTED]> wrote:
> Yes I'm aware of that problem and it's great to hear you might have a
> solution to it.
Well, this works now:
/////////////////////////////////////////////
instance[T,U] Str[T * U] {
fun str (x:T, y:U)=> str x + ", " + str y;
}
instance Str[unit] {
fun str() => "";
}
println$ str (1,(2,("3",())));
////////////////////////////////////////////////
$ f s2
1, 2, 3,
//////////////////////////////////////////////////
Unfortunately this:
instance[T] Str[T*unit] {
fun str( x:T,y:unit) => str x;
}
gives:
Unimplemented: Multiple matching instances for typeclass virtual
instance
str<1898>[string<2133> * unit]
Function 4818 instance parent 4814
SYSTEM FAILURE
Woops can't find instance 4814
Haskell doesn't allow this either, although I think GHC does.
The algorithm of choice is the same one used for overloading:
allow overlapping instances and use the most specialised one.
--
John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net
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