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Polymorphic map and OO syntax extension
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Date: -- (:)
From: Jacques Garrigue <garrigue@m...>
Subject: Polymorphic map and OO syntax extension
Hello camlers,

I've just put together some code bits I thought my be interesting for
others.

You can find them at
  http://www.math.nagoya-u.ac.jp/~garrigue/code/ocaml.html

OO syntax extension
    Some camlp4 syntax extensions to write more compact code using
    objects. The new syntaxes are
        * val [mutable] x = expr with (reader|writer|accessor)
          generates code for an x and a set_x method, like in ruby.
        * obj#x <- expr
          generates a call to the set_x method.
        * {| [mutable] f1 = expr1; ...; [mutable] fn = exprn |}
          generates an immediate object with the above fields and the
          corresponding accessor methods. You may also include inherit
          declarations.  

Polymap
    This is a tiny module combined with a camlp4 extension, which
    allows you to define polymorphic mappings, where the type of the
    data depends on the key. (The syntax is strange, but I had no
    better idea.)
        $ ocaml camlp4o.cma pa_polymap.cmo polymap.cmo
        # let m = `{x=1; y=true};;
        val   m : [> `x of int | `y of bool ] Polymap.t = 
        # let m = `{m with z = "hello"};;
        val m : [> `x of int | `y of bool | `z of string ] Polymap.t = 
        # m.`y;;
        - : bool = true
        # `{m with x = "a"};;
            ^
        Types for tag `x are incompatible
        # m.`u;;
        Exception: Not_found.

---------------------------------------------------------------------------
Jacques Garrigue      Nagoya University     garrigue at math.nagoya-u.ac.jp
		   <A HREF=http://www.math.nagoya-u.ac.jp/~garrigue/>JG</A>