Ola! Currently we have:
type family If cond tru fls where
If True tru fls = tru
If False tru fls = fls
Unfortunately, this appears to turned into a monomorphicly kinded type family
by GHC, which means it’s impossible to do
foo :: If cond () (“Condition does not hold” ~ “”) => Foo -> Bar
or similar fancy constraints.
I hereby propose altering If to:
type family If (cond :: Bool) (tru :: k) (fls :: k) :: k where
If True tru fls = tru
If False tru fls = fls
Allowing it to work with kinds other than *.
Discussion period: 2 weeks? Seems like a minor change.
Cheers,
Merijn
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