Re: [Caml-list] elegant subtyping?

[Pietro Abate <Pietro.Abate@pps.jussieu.fr>]

hello,
using polymorphic variants maybe ?

# module Cfg =  struct type statement = [ `Assign | `Guard ] end;;
module Cfg : sig type statement = [ `Assign | `Guard ] end

# module Ast =  struct type statement = [ Cfg.statement | `Goto | `Label ] end;;
module Ast : sig type statement = [ `Assign | `Goto | `Guard | `Label ] end

p

On Fri, Nov 04, 2011 at 02:06:23PM +0100, Markus Weißmann wrote:
> 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
> 
> -- 
> Markus Weißmann, M.Sc.
> Institut für Informatik
> Technische Universität München
> Raum 03.07.054, Boltzmannstr. 3, 85748 Garching
> 
> Tel. +49 (89) 2 89-1 81 05
> Fax +49 (89) 2 89-1 81 07
> 
> mailto:markus.weissmann@in.tum.de
> 
> 
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