On Wed, 16 Sep 2009, David Matthews wrote:
To be honest, when I think of an abstract type I think of the abstype
construction rather than opaque signature matching.
In fact, we are more used to SML90-style signature matching anyway. Some
opaque matches were introduced only recently to ensure that certain types
loose equality status.
At an intermediate state, I've also tried abstype, but discontinued it
again at the point where a structure definition within its body was
required. This appears to be illegal, probably because abstype is much
older than the structure/signature/functor layer in ML.
Interestingly, opaque signature matching also causes problems in SML/NJ
pretty printing. I consider to make another attempt at abstype within a
non-opaque structure, trying to avoid the nested structure within the
abstract type.
Makarius
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