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Compute a mapped type family's image at the use site - #61
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typeFamiliesToMapToTypeScript only handled a single-argument family with a concrete image, so
a mode-indexed family whose result is one of its own arguments was rejected outright:
type family IsHydrated (f :: Type -> Type) x y where
IsHydrated Dry x y = x
IsHydrated Wet x y = y
The use site fixes those arguments, and then the image is concrete. Substituting them before
tabulating turns such a record into one generic declaration indexed on the mode, rather than
one specialized declaration per instantiation sharing a name.
A variable that keys a mapped family is now an eligible generic variable whatever its kind,
tables are named per use site so two sites of one family don't collide, and the placeholder
each table generates is memoized per module.
Still out of reach: a family whose choice type mentions another of the record's variables, and
one whose keys aren't plain constructors (beam's Columnar).
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typeFamiliesToMapToTypeScript only handled a single-argument family with a concrete image, so a mode-indexed family whose result is one of its own arguments was rejected outright:
type family IsHydrated (f :: Type -> Type) x y where
IsHydrated Dry x y = x
IsHydrated Wet x y = y
The use site fixes those arguments, and then the image is concrete. Substituting them before tabulating turns such a record into one generic declaration indexed on the mode, rather than one specialized declaration per instantiation sharing a name.
A variable that keys a mapped family is now an eligible generic variable whatever its kind, tables are named per use site so two sites of one family don't collide, and the placeholder each table generates is memoized per module.
Still out of reach: a family whose choice type mentions another of the record's variables, and one whose keys aren't plain constructors (beam's Columnar).