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890 B
This tests an issue where ability variables were being defaulted over eagerly. In general, we want to avoid collecting up variables from the use of definitions with types like:
T ->{e} U
Since this type works for every e
, it is, 'pure;' and we might as
well have e = {}
, since {}
is a subrow of every other row.
However, if e
isn't just a quantified variable, but one involved in
ongoing inference, it's undesirable to default it. Previously there
was a check to see if e
occurred in the context. However, the wanted
abilities being collected aren't in the context, so types like:
T ->{S e} U ->{e} V
were a corner case. We would add S e
to the wanted abilities, then
not realize that e
shouldn't be defaulted.
unique ability Storage d g where
save.impl : a ->{Storage d g} ('{g} (d a))
save : a ->{Storage d g, g} (d a)
save a = !(save.impl a)