On 06/07/2010 09:48 PM, David Allsopp wrote: > Török Edwin wrote: >> What is the recommended way to convert a variant that has only constant >> constructors to an integer? (an integer that is unique for each constant >> constructor, preferably sequential in the order in which they are >> declared). > > type foo = A | B;; > external int_of_foo : foo -> int = "%identity";; > > Which is another way of saying Obj.magic - but %identity is an OCaml > primitive, where Obj.magic is part of a restricted module so there is a > small semantic difference in terms of future support. The internal > representation of variants won't change until at least OCaml 4.0.0 - > there're simply far too many C bindings out there! foo_of_int obviously > can't be done quite so trivially written although having checked that the > int represents a valid constructor you can then use %identity in the same > way.
Thanks, that "%identity" looks exactly what I wanted. I don't need a foo_of_int right now. On 06/07/2010 09:45 PM, bluestorm wrote: > 2010/6/7 W Dan Meyer <wojciech.me...@googlemail.com > <mailto:wojciech.me...@googlemail.com>> >> I can imagine you could use an association list, function with pattern >> matching, code generation tool (based on CamlP4), etc. > > I wrote a type-conv ( > http://www.ocaml.info/home/ocaml_sources.html#type-conv ) generator for > just that a few years ago : > http://bluestorm.info/camlp4/ty_enum_to_int.ml.html > > Example use : > > type test = | A | B | C | D of bool with to_int > > > Generated functions : > > let test_to_int = function | A -> 0 | B -> 1 | C -> 2 | D _ -> 3 > > let test_of_int = function > | 0 -> A > | 1 -> B > | 2 -> C > | 3 -> failwith "can't convert to a constructor with parameters: D" > | _ -> invalid_argument "test_of_int" > If I'll need a foo_of_int this sounds like a good solution, thanks. Best regards, --Edwin _______________________________________________ Caml-list mailing list. Subscription management: http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list Archives: http://caml.inria.fr Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs
