src/Literate/Accounting/Unit.hs

   1 {-# LANGUAGE AllowAmbiguousTypes #-}
   2
   3 module Literate.Accounting.Unit where
   4
   5 import Literate.Prelude
   6 import Text.Show (ShowS, showParen, showString)
   7
   8 data Unit where
   9   UnitName :: Symbol -> Unit
  10   (:*:) :: Unit -> Unit -> Unit
  11   (:/:) :: Unit -> Unit -> Unit
  12
  13 class UnitShowS (u :: Unit) where
  14   unitShowS :: Int -> ShowS
  15 instance KnownSymbol u => UnitShowS (UnitName u) where
  16   unitShowS _prec = showString (symbolVal (Proxy @u))
  17 instance (UnitShowS x, UnitShowS y) => UnitShowS (x :*: y) where
  18   unitShowS p = showParen (7 <= p) $ unitShowS @x 7 . showString "\x202F*\x202F" . unitShowS @y 7
  19 instance (UnitShowS x, UnitShowS y) => UnitShowS (x :/: y) where
  20   unitShowS p = showParen (7 <= p) $ unitShowS @x 7 . showString "\x202F/\x202F" . unitShowS @y 7
  21
  22 unitShow :: forall u. UnitShowS u => String
  23 unitShow = unitShowS @u 0 ""