[m-dev.] dummy types with user-defined equality/comparison

[Ralph Becket]

Julien Fischer, Monday, 29 May 2006:
> 
> Currently the compiler will abort when confronted with a dummy type that has
> user-defined equality or comparison.  Below are two proposals for fixing
> this.  Which do people prefer?
> 
> (1) Change the reference manual to say that discriminated union types
>     whose body consists of a single zero-arity constructor may not have
>     user-defined equality or comparison defined upon them.  (Plus change
>     the compiler to emit the appropriate error mesages.)
> 
> (2) Change the compiler so that it does not treat discriminated union types
>     whose body consists of a single zero-arity constructor as dummy types.

I'd argue for (1): dummy-types is a useful optimization and this
situation is so rare that I can't see the restriction affecting anyone.
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