Rob,
Actually what I was trying to find was the bit that says that the
equality attribute in a type variable used as a datatype parameter
should be honoured where it isn't when used as a type parameter.
> type ''a t = ''a * ''a;
type 'a t = 'a * 'a
> (1.0, 2.0): real t;
val it = (1.0, 2.0): real t
> datatype ''a t = C of ''a;
datatype 'a t = C of ''b <<<< This prints wrongly
> C 1.0;
poly: : error: Type error in function application.
Function: C : ''a -> ''a t
Argument: 1.0 : real
Reason: Can't unify ''a to real (Requires equality type)
Found near C 1.0
Static Errors
I'm sure I looked into this a long time ago and a check with hamlet
agrees with Poly/ML so I'm confident it's right; I just haven't been
able to find the reference.
Regards,
David
On 16/09/2016 20:18, Rob Arthan wrote:
David,
On 16 Sep 2016, at 19:19, David Matthews <[email protected]> wrote:
I've checked hamlet and mlton and they both reject it so I think in this case
Poly/ML is right and SML/NJ is wrong. I can't point to the bit of the
definition that says that, though.
It's in Appendix C: "Of [the type names listed in the initial static basis] all
except exn and real admit equality".
Regards,
Rob.
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