Hello, First, you really need strong tyupe checking because your definition is actually incorrect.
Second, see polymorphic-recursion : http://alaska-kamtchatka.blogspot.com/2009/05/polymorphic-recursion.html Be sure to read the comments by bluestorm. There is also pa_polyrec, a syntax extension for polymorphic recursion in OCaml : http://www.mail-archive.com/caml-list@yquem.inria.fr/msg04795.html Finally, here is your (corrected) code using vanilla ocaml : type map = { map : 'a 'b. ('a -> 'b) -> 'a t -> 'b t } let map = let rec map = { map = fun f -> function | E -> E | D (t1, t2) -> D (map.map f t1, map.map f t2) | O a -> O (f a) | I tt -> I (map.map (map.map f) tt) } in map.map - damien Le 17/02/2010 à 17:34:24, "Stéphane Gimenez" <stephane.gime...@pps.jussieu.fr> à écrit : > >Hi, > >I just realized that ocaml generalizes the type of a recursively >defined function *only* for calls which are outside it's own >definition. Recursive calls cannot use a generalized type. > >In fact, I'm tring to work with such a data type: > >type 'a t = > | E > | D of 'a t * 'a t > | O of 'a > | I of 'a t t > >And, I'm forced to use some dark magic to define simple operations on >it: > >let rec map (f : 'a -> 'b) : 'a t -> 'b t = > begin function > | E -> E > | D (t1, t2) -> D (map f t1, map f t2) > | O a -> O (f a) > | I tt -> > I ((Obj.magic map : ('a t -> 'b t) -> 'a t t -> 'b t t) (map f) tt) > end > >Questions: > - Is it theoreticaly safe to generalize recursive calls ? > - Is there a syntactical trick to use generalized recursive calls ? > - Could such a generalization be added to the type checker ? > - Performance issues ? > - More obfusctated type checking errors ? > >In a related disscution I found, one asked about generalization >between mutualy recursive definitions (same problem). No answers, but >maybe I just lack pointers. > >Cheers, >Stéphane > >_______________________________________________ >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 > -- Mail created using EssentialPIM Free - www.essentialpim.com _______________________________________________ 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
