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992 B
992 B
Tests an improvement to type checking related to abilities.
foo
below typechecks fine as long as all the branches are checked
against their expected type. However, it's annoying to have to
annotate them. The old code was checking a match by just synthesizing
and subtyping, but we can instead check a match by pushing the
expected type into each case, allowing top-level annotations to act
like annotations on each case.
scratch/main> builtins.merge
ability X a where yield : {X a} ()
ability Y where y : ()
type Foo b a = One a
type Bar a
= Leaf a
| Branch (Bar a) (Bar a)
f : (a -> ()) -> '{g, X a} () -> '{g, X a} () -> '{g, X a} ()
f _ x y = y
abra : a -> '{Y, X z} r
abra = bug ""
cadabra : (y -> z) -> '{g, X y} r -> '{g, X z} r
cadabra = bug ""
foo : Bar (Optional b) -> '{Y, X (Foo z ('{Y} r))} ()
foo = cases
Leaf a -> match a with
None -> abra a
Some _ -> cadabra One (abra a)
Branch l r ->
f (_ -> ()) (foo l) (foo r)