Re: [q-lang-users] Types and multiple inheritance

[Albert G. <Dr....@t-...>]

Hi, John,

John.Cowan wrote:
> As I understand it, variable references with a type guard T match only
> expressions whose operators are declared in the type declaration for T
> or inherited from T's supertype, if any.

s/operators/constructors/

Nope, it's just the other way round. A variable of type T matches the 
constructor patterns of T itself, as well as those of all its 
_subtypes_. So that effectively makes the supertype the union of all of 
its subtypes.

Conversely, with multiple inheritance you'd have that a certain 
constructor pattern would match different supertypes (i.e., the common 
subtype belongs to the intersection of its supertypes). That does make 
perfect sense. (It won't buy you much, though, unless you design all 
involved datatypes as ADTs, but I take this for granted when you're 
programming the OOP way.)

At least the pattern matching automaton generator algorithm in the 
bytecode compiler and the runtime symbol table would have to be changed 
to accommodate for this. That should be doable, but, as it won't be a 
walk in the park to implement this in an efficient manner, please 
understand that it's not very high on my priority list, until someone 
comes up with a good usage scenario. ;-)

Cheers,
Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikwissenschaft.uni-mainz.de/~ag