uom-plugin lesson

gistfile1.hs

{-# OPTIONS_GHC -fplugin Data.UnitsOfMeasure.Plugin #-}
{-# LANGUAGE DataKinds, QuasiQuotes, TypeOperators #-}
{-# LANGUAGE TypeFamilies, UndecidableInstances #-}

import Data.UnitsOfMeasure

main :: IO ()
main = print ([u| 3 m  |] :: Quantity Int [u| m |])


{-

(7.10.1)nushio@nuwheezy:uom-plugin$ ghc learn.hs
[1 of 1] Compiling Main             ( learn.hs, learn.o )

learn.hs:8:8:
    No instance for (Data.UnitsOfMeasure.Singleton.KnownUnit
                       (Unpack (MkUnit "m")))
      arising from a use of ‘print’
    In the expression:
      print
        ((Data.UnitsOfMeasure.Internal.MkQuantity ::
            forall a_a4cE. a_a4cE -> Quantity a_a4cE (MkUnit "m")
          3) ::
           Quantity Int (MkUnit "m"))
    In an equation for ‘main’:
        main
          = print
              ((Data.UnitsOfMeasure.Internal.MkQuantity ::
                  forall a_a4cE. a_a4cE -> Quantity a_a4cE (MkUnit "m")
                3) ::
                 Quantity Int (MkUnit "m"))
(7.10.1)nushio@nuwheezy:uom-plugin$

-}