after.hs

genDefunSymbols [''Leverage]
promoteOnly
  [d|
    validLeverageAmt :: Nat -> Symbol -> Symbol -> ()
    validLeverageAmt l b q =
      if l `elem` leverage b q
        then ()
        else
          typeError
            ( ShowType l
                :<>: Text " is not an available leverage multiplier for pair "
                :<>: Text b
                :<>: Text "/"
                :<>: Text q
            )
    |]

type ValidLeverage l b q =
  ( KnownNat l,
    MarginPair b q,
    ValidLeverageAmt l b q ~ '()
  )

before.hs

type family ValidLeverageAmt l b q s :: Constraint where
  ValidLeverageAmt l b q '[] =
    TypeError
      ( 'ShowType l
          ':<>: 'Text " is not an available leverage multiplier for pair "
          ':<>: 'Text b
          ':<>: 'Text "/"
          ':<>: 'Text q
      )
  ValidLeverageAmt l b q (l ': s) = ()

type ValidLeverage l b q =
  ( KnownNat l,
    MarginPair b q,
    ValidLeverageAmt l b q (Leverage b q)
  )