throwing syntax sugar

[reactormonk]

Also added a test.

[natefaubion]

I think this can be formulated without expand:

class VariantInjTagged a b | a -> b where
  injTagged :: Record a -> Variant b

instance variantInjTagged ::
  ( RowToList r1 (RL.Cons sym a RL.Nil)
  , R.Cons sym a () r1
  , R.Cons sym a rx r2
  , IsSymbol sym
  ) =>
  VariantInjTagged r1 r2 where
  injTagged = inj (SProxy :: SProxy sym) <<< get (SProxy :: SProxy sym)

This would allow you to just write throw as:

throw :: forall m r1 r2 a.
  VariantInjTagged r1 r2 =>
  MonadThrow (Variant r2) m =>
  Record r1 ->
  m a
throw = throwError <<< injTagged

I know I originally said that I didn't really want this sugar in Variant core, but I might reconsider. It does seem a but weird to stick this here.

[safareli]

natefaubion/purescript-variant#44