Quoting "Wolfgang Jeltsch" <g9ks1...@acme.softbase.org>:
Am Mittwoch, den 28.12.2011, 12:48 +0000 schrieb Simon Peyton-Jones:
Only that BOX is a sort (currently the one and only sort), whereas
Constraint is a kind. I'm not sure that BOX should ever be displayed
to users.
Okay, this makes sense then. However, note that the GHC User’s manual
mixes the terminology (“kind” vs. “sort”) at one point:
Note that List, for instance, does not get kind BOX -> BOX, because
we do not further classify kinds; all kinds have sort BOX.
I think, it should say “sort BOX -> BOX”.
I don't think that would be quite correct. Sorts are typically
constants, and there are usually a finite amount of them, each
presenting a "level" of the type system. For instance, * and BOX are
both sorts, even though we also have * :: BOX. In a system where BOX
-> BOX would be well-formed, it should probably be called something
else, maybe "kind-classifying term" (whose sort would be something
new, maybe TRIANGLE).
But it seems a bit funny to spend a lot of time thinking about what to
call things that don't exist in GHC. Maybe it'd be easiest to just
drop that awkward hypothetical "BOX -> BOX" altogether from the manual.
Lauri
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