generic data type -> int function

[Hal Daume III <hdaume@ISI.EDU>]

Hi all --

Is there a straightforward way (or a built in function, or...) to 
automatically map an enumerated data type to integers (and back, if 
possible, but that's not strictly necessary).  In particular, I need 
something like:


type a = A | B | C | D
type b = E | F | G 
type c = H of a | I of b

and I would like to automatically have three functions:

let a_to_int = function
  A -> 0 | B -> 1 | C -> 2 | D -> 2

let b_to_int = function
  E -> 0 | F -> 1 | G -> 2

let c_to_int = function
   H a -> a_to_int a
 | I b -> 3 + b_to_int b

obviously in this case it's simple, but if now i add a "D2" to 'a', 
everything gets screwed up.

Is there a build in magic function that will do this, or some way to do 
this otherwis (like with camlp4 or something)?

Thanks in advance -- 

 - Hal


-- 
 Hal Daume III                                   | hdaume@isi.edu
 "Arrest this man, he talks in maths."           | www.isi.edu/~hdaume