{-# LANGUAGE AllowAmbiguousTypes #-}

module Literate.Accounting.Unit where

import Literate.Prelude
import Text.Show (ShowS, showParen, showString)

data Unit where
  UnitName :: Symbol -> Unit
  (:*:) :: Unit -> Unit -> Unit
  (:/:) :: Unit -> Unit -> Unit

class UnitShowS (u :: Unit) where
  unitShowS :: Int -> ShowS
instance KnownSymbol u => UnitShowS (UnitName u) where
  unitShowS _prec = showString (symbolVal (Proxy @u))
instance (UnitShowS x, UnitShowS y) => UnitShowS (x :*: y) where
  unitShowS p = showParen (7 <= p) $ unitShowS @x 7 . showString "\x202F*\x202F" . unitShowS @y 7
instance (UnitShowS x, UnitShowS y) => UnitShowS (x :/: y) where
  unitShowS p = showParen (7 <= p) $ unitShowS @x 7 . showString "\x202F/\x202F" . unitShowS @y 7

unitShow :: forall u. UnitShowS u => String
unitShow = unitShowS @u 0 ""