HaloO Autrijus,
you wrote:
On Fri, May 13, 2005 at 07:13:53PM +0200, "TSa (Thomas Sandlaß)" wrote:
Larry Wall wrote:
: Void context still exists and is not a form of singular or plural : context. Perhaps this should be called nullar context, although void : context works equally well for me and is not confusing because we have : no Void type.
Nice, without Void we don't need the double headed pseudo type lattice needed if we were to distinguish subs that return no usefull---that is Any---value from the ones that return no value at all.
Hrm. So if I have a sub that does nothing:
sub Foo { }
I don't know what the empty body does. But it might just return an undef value.
Is it illegal to say this?
sub Foo returns Void { }
Well, $Larry said that there's no Void type. Thus it's illegal unless of course some non-standard class bears that name which would be a bit odd.
What about:
sub Foo returns :() { }
Ups, looks quite void to me. So, this might prevent e.g.
$x = Foo();
by giving a static type error. OTOH, @Larry might argue that it's one way to write :(Any).
Or do I really need to convert it to this?
sub Foo returns Any { }
The only reason to distinguish the topmost type from Void is that it can't be used as a value e.g. in an assignment.
OTOH such a Code subtype should be easily subtypable, and the return type is covariant like the invocants, but the non-invocants are contra-variant. So, assuming Bit <: Int <: Num <: Any, and <: beeing the subtype relation, and using the --> for function types, this means e.g.
:( Bit,Int : Int,Num --> Int ) <: :( Int,Int : Bit,Int --> Num )
In words: 1) :(Bit,Int) is more specific than :(Int,Int) for MMD 2) :(Int,Num) is more general than :(Bit,Int) for type safety on call 3) :(Int) can go were a :(Num) is expected as return type
Subtyping :(: Any --> ) 'sub with param type Any returning void' wouldn't work if Void is the bottommost type or outside the type system.
Actually I still wonder if the type system will work as indicated above at all. P6l might find that too B&D-ish. -- TSa (Thomas Sandlaß)
