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Add instance for converting from rational into fixed

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This commit is contained in:
Taylor Fausak 2021-07-10 15:29:03 -04:00
parent 09888d81a2
commit aac3a0e755
2 changed files with 18 additions and 0 deletions
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9
src/lib/Witch/Instances.hs
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@ -1,6 +1,7 @@
{-# OPTIONS_GHC -Wno-orphans #-} {-# OPTIONS_GHC -Wno-orphans #-}
{-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-} {-# LANGUAGE TypeApplications #-}
module Witch.Instances where module Witch.Instances where
@ -907,6 +908,14 @@ instance From.From Rational Float where
instance From.From Rational Double where instance From.From Rational Double where
from = fromRational from = fromRational
-- | TODO
instance Fixed.HasResolution a => TryFrom.TryFrom Rational (Fixed.Fixed a) where
tryFrom = Utility.eitherTryFrom $ \s ->
let t = fromRational s :: Fixed.Fixed a
in if toRational t == s
then Right t
else Left Exception.LossOfPrecision
-- Fixed -- Fixed
-- | Uses 'Fixed.MkFixed'. This means @from \@Integer \@Centi 2@ is @0.02@ -- | Uses 'Fixed.MkFixed'. This means @from \@Integer \@Centi 2@ is @0.02@

9
src/test/Main.hs
View File

@ -1448,6 +1448,15 @@ main = runTestTTAndExit $ "Witch" ~:
, f 0.5 ~?= 0.5 , f 0.5 ~?= 0.5
, f (-0.5) ~?= (-0.5) , f (-0.5) ~?= (-0.5)
] ]
, "TryFrom Rational (Fixed a)" ~:
let f = hush . Witch.tryFrom @Rational @Fixed.Deci in
[ hush (Witch.tryFrom @Rational @Fixed.Uni 1) ~?= Just 1
, hush (Witch.tryFrom @Rational @Fixed.Uni 1.2) ~?= Nothing
, f 0.1 ~?= Just 0.1
, f 1.2 ~?= Just 1.2
, f 12.3 ~?= Just 12.3
, f 0.12 ~?= Nothing
]
-- Fixed -- Fixed