good fixed witch instances

Author: functora

pub/functora-witch/source/library/Functora/Witch/Instances.hs

@@ -11,6 +11,7 @@ module Functora.Witch.Instances where
 
 import qualified Control.Exception as Exception
 import qualified Control.Monad as Monad
+import qualified Data.Bifunctor as Bifunctor
 import qualified Data.Bits as Bits
 import qualified Data.ByteString as ByteString
 import qualified Data.ByteString.Char8 as Char8
@@ -936,24 +937,31 @@ instance (Fixed.HasResolution a) => TryFrom.TryFrom Rational (Fixed.Fixed a) whe
 
 -- Fixed
 
---
--- TODO : update after fix https://github.com/tfausak/witch/issues/121
---
-
--- -- | Uses 'Fixed.MkFixed'. This means @from \@Integer \@Centi 2@ is @0.02@
--- -- rather than @2.00@.
--- instance From.From Integer (Fixed.Fixed a) where
---   from = Fixed.MkFixed
+-- | Uses 'fromInteger'. This means @from \@Integer \@Centi 2@ is @02.00@
+-- rather than @0.02@.
+instance (Fixed.HasResolution a) => From.From Integer (Fixed.Fixed a) where
+  from = fromInteger
 
--- -- | Uses 'Fixed.MkFixed'. This means @from \@Centi \@Integer 3.00@ is @300@
--- -- rather than @3@.
--- instance From.From (Fixed.Fixed a) Integer where
---   from (Fixed.MkFixed t) = t
+-- | Converts via 'Rational' when there is no fractional part. This means
+-- @tryFrom \@Centi \@Integer 2.00@ is @Right 2@ and
+-- @tryFrom \@Centi \@Integer 0.02@ will fail.
+instance (Fixed.HasResolution a) => TryFrom.TryFrom (Fixed.Fixed a) Integer where
+  tryFrom = Utility.eitherTryFrom $ TryFrom.tryFrom @Rational . From.from
 
 -- | Uses 'toRational'.
 instance (Fixed.HasResolution a) => From.From (Fixed.Fixed a) Rational where
   from = toRational
 
+-- | Converts via 'Rational'.
+instance
+  (Fixed.HasResolution s, Fixed.HasResolution t) =>
+  TryFrom.TryFrom (Fixed.Fixed s) (Fixed.Fixed t)
+  where
+  tryFrom s =
+    Bifunctor.first (Utility.withSource s)
+      . TryFrom.tryFrom @Rational
+      $ From.from s
+
 -- Complex
 
 -- | Uses '(Complex.:+)' with an imaginary part of 0.