On Tue, Feb 26, 2019 at 03:39:24PM +0900, Jacques Garrigue wrote:

2019/02/26 15:23, Hendrik Boom <hendrik@topoi.pooq.com>:

I have a (broken) function definition starting:

let mixfix : 'token1 'phrase1.
('token1, 'phrase1, ('token1, 'phrase1) Phrasestream.phrasestream) grammar
      -> ('token1, 'phrase1) parser
 =  fun gram -> (
...

It goes o for a hundred-odd lines.
The type-parameterized types Phrasestream.phrasestream, grammar, and parser   
have been previously defined, and there are also operations defined on these
types.

The problem I'm having is that the OCaml type-checker ends up identifying
the type parameters 'token1 an 'phrase1 because of type errors I've made in
the body of the mixfix function.  Somewhere I ended up using an
operator that's supposed to work on values of type 'token1
on a value of type 'phrase1 instead, and identification of 'token1 and 
'phrase1 is the natural result.

Is there some way of forcing the type checker to treat 'token1 and 
'phrase1 as different types so that I can get meaningful type errors
at the point were they occur?

You can use locally abstract types, which are often used with GADTs but are not
restricted to them:
 let mixfix : type token1 phrase1.
   (token1, phrase1, (token1, phrase1) Phrasestream.phrasestream) grammar
      -> (token1, phrase1) parser
 =  fun gram -> (

Thus *with* the type keyword, but *without* the apostrophes on token1 
and phrase1?