Re: [Caml-list] elegant subtyping?

[Matthias Puech <puech@cs.unibo.it>]

Isn't that exactly what polymorphic variants are for?
http://caml.inria.fr/pub/docs/manual-ocaml/manual006.html#toc36
Cheers,
     -m

Le 11/04/2011 02:06 PM, Markus Weißmann a écrit :
> Hello everyone,
>
> I'm writing on a compiler and want to subtype the "statements" that can
> occur in my code:
> At first I have an abstract syntax tree that can hold any statement of the
> language. From that I create a control flow graph that will only have
> non-control-flow statements (a true subset of the Ast-statements).
> Whats the best way to realize that?
>
> Basically I have:
>
> module Ast: type statement = Assign | Guard | Goto | Label
> module Cfg: type statement = Assign | Guard
>
>
> I see three -- not so elegant -- solutions to this:
>
> 1.) type-safe but imho quite ugly code:
> module Cfg: type statement = Assign | Guard
> module Ast: type statement = Base of Cfg.statement | Goto | Label
>
> 2.) use the same type for both and give up the safety that wrong types
> cannot show up in the Cfg
>
> 3.) use objects
>
> Did I miss the type-safe, elegant, module-based solution somehow? Or is
> 1.) as good as it gets?
>
>
> Best regards
>
> -Markus
>