Re: My scripting language - any suggestions?

On Wed, Sep 3, 2008 at 12:22 AM, Dmitry A. Kazakov
<mailbox@dmitry-kazakov.de> wrote:
> On Tue, 2 Sep 2008 00:54:12 +0700, Aleksey Demakov wrote:
>> Suppose we have a method that simply returns the sum of two args:
>>
>> m(a, b) { return a + b; }
>
> First of all, this is not a specification of the method. The types of the
> arguments and of the result are unspecified, as well as the covariance of.
> So one cannot tell which combinations of arguments and result types are
> involved.
>


We were talking in the context of a scripting language. If you notice
the variables in this language are declared as "var a = 5;". No type
tag whatsoever. I don't see a reason why for such a language
parameters are to be declared with the type tag. But if you wish I
could write the method definition like this:


Float m(Float a, Float b) { return a + b; }


> As for multimethods, yes there are six combinations of 3 (2 arguments + 1
> result) x 2 types. The semantics of m shall unambiguously define all six.
> But again it is not the language business, except for the predefined
> operations of course. The language shall merely allow an implementation of
> the desired semantics for all combinations in question.
>


What do multimethods have to do with this? You say that a language
"with an elaborated types system" should make integer a subtype
of float. My understanding of subtyping is that a subtype might go
anywhere the supertype could go. I conclude that there is no need for
any 6 combinations. The method defined for float arguments should
somehow handle int arguments too.


> The result is involved, provided that m is covariant, or else when Float is
> the ancestor of Integer and the result is contravariant. As for the
> semantics (numerical value of the result), see above.
>


I don't get what "covariant" or "contravariant" mean. I asked a simple
question. Please tell me what a language "with an elaborated types
system" will do for m(1, 2000000000,0) .


Regards,
Aleksey

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