[q-lang-users] Multiple supertypes for Q?

[John C. <co...@cc...>]

Multiple supertypes would seem to be fairly cheap and easy to add to Q.
Declaring "type Bar : Foo" just means that the constructors of Bar will
match a variable with a Foo type guard.  If we further declare "type Baz :
Foo", that further adds the constructors of Baz to what X:Foo will match.
So there seems to be no obvious reason why "type Toto : Tata, Titi, Tutu"
shouldn't add Toto's constructors to the constructors matching X:Tata,
X:Titi, and X:Tutu.

This may be very expensive in the implementation for reasons I don't know
about, but if experience with Java interfaces and C abstract classes
is correct, it will not be used often but will be indispensable in
some cases.

Here are a few ideas for new built-in types assuming #1 is adopted,
borrowed from built-in Haskell type classes:

	Eq: for types on which = is defined;
	Ord: for types (including enums) on which < etc. are defined;
	Ix: for types on which ! is defined.

-- 
John Cowan   co...@cc...    http://ccil.org/~cowan
Original line from The Warrior's Apprentice by Lois McMaster Bujold:
"Only on Barrayar would pulling a loaded needler start a stampede toward one."
English-to-Russian-to-English mangling thereof: "Only on Barrayar you risk to
lose support instead of finding it when you threat with the charged weapon."