[Caml-list] elegant subtyping?

["Markus Weißmann" <markus.weissmann@in.tum.de>]

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