[wg-camlp4] Changes to the parsetree

[Leo White]

> Do you know if it would be difficult to adapt the type-checker to support arbitrary types in place of parameters (with
> the same semantics as constraints, I guess)?  If this fits nicely in the current type-checker, it would be a good
> argument to support arbitrary types in the Parsetree and the concrete syntax.

I don't think that it is difficult for the type-checker to support it,
but it is awkward for the parser. I'm also not sure that it is a
desirable change. I think that

  type 'a t constraint 'a = 'b list

is probably more readable than

  type 'a list t