Record subset

SubsetRecord.purs

class RowSubset (row :: # Type) (xs :: RowList) (subrow :: # Type) | xs -> subrow where
  subsetImpl :: RLProxy xs -> {|row} -> {|subrow}

instance nilRowSubset :: RowSubset row Nil () where subsetImpl _ _ = {}

instance consRowSubset
  ::
  ( IsSymbol sym
  , Cons sym a subrowWithoutSym subrowWithSym
  , Cons sym a srcWithoutSym src
  , Lacks sym subrowWithoutSym
  , RowSubset src rl subrowWithoutSym
  ) => RowSubset src (Cons sym a rl) subrowWithSym where
  subsetImpl _ src = insert (SProxy :: SProxy sym) (get (SProxy :: SProxy sym) src) (subsetImpl (RLProxy :: RLProxy rl) src)

subsetRow
  :: ∀ rl subR src
  . ListToRow rl subR
  => RowToList subR rl
  => RowSubset src rl subR
  => {|src}
  -> RProxy subR
  -> {|subR}
subsetRow src _ = subsetImpl (RLProxy :: RLProxy rl) src