Luca Pascali wrote:
> # let a = `Hi;;
> val a : [> `Hi ] = `Hi
> -------------------^    I'd like to have this string
> 
> I tried using the Obj module, but I got only segmentation faults.
> I know that the Obj module has not to be used, but what I want to write
> will be placed into a library with a signature like this:
> 
> val string_of_polymorphic : [> `Dummy ] -> string

Ciao Luca,

I have a solution to the problem: it requires Camlp4. It is possible to 
build a syntax extension such that

type poly = [ `Pizza | `Pie ]

actually compiles down to

type poly = [ `Pizza | `Pie ]
let string_of_poly = function
   | `Pizza -> "Pizza"
   | `Pie -> "Pie"


Let me refer you to the relevant documentation:
http://caml.inria.fr/camlp4/manual/manual005.html#toc11

A similar job is done by IoXml. Take a look at it: you probably want to 
start out by modifying Daniel's code rather than starting from scratch.
http://pauillac.inria.fr/~ddr/IoXML/

Have fun!
Alex

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