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Add PolyKinds to Clash.Class.BitPack.Internal #2993

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Add PolyKinds to Clash.Class.BitPack.Internal #2993

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c5e357d
Add `PolyKinds` to `Clash.Class.BitPack.Internal`
lmbollen Aug 21, 2025
fd38330
Add regression doctests for `BitPack (Proxy a)`
lmbollen Aug 21, 2025
1c193ad
Remove superfluous `Bitpack (Proxy a)` constraint from `BitPack (Prox…
lmbollen Aug 25, 2025
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13 changes: 11 additions & 2 deletions clash-prelude/src/Clash/Class/BitPack/Internal.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,7 @@ Maintainer : QBayLogic B.V. <[email protected]>
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE UndecidableInstances #-}

{-# LANGUAGE PolyKinds #-} -- Required for BitPack (KnownNat n) => BitPack (Proxy n) instances
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Sorry I missed this on initial review, but what does BitPack (KnownNat n) mean? I initially mentally autocorrected this to KnownNat n => BitPack (Proxy n) which makes sense although it is overly specific: it forces n to be a Nat which needs PolyKinds. How about:

Suggested change
{-# LANGUAGE PolyKinds #-} -- Required for BitPack (KnownNat n) => BitPack (Proxy n) instances
{-# LANGUAGE PolyKinds #-} -- Required for BitPack (Proxy (n :: Nat)) instances

It's still overly specific, but at least it makes sense. I don't think a BitPack (KnownNat n) constraint means anything?

{-# LANGUAGE Trustworthy #-}

{-# OPTIONS_GHC -fplugin=GHC.TypeLits.Extra.Solver #-}
Expand Down Expand Up @@ -58,6 +58,7 @@ import Clash.Sized.Internal.BitVector
>>> :m -Prelude
>>> :set -XDataKinds
>>> import Clash.Prelude
>>> import Data.Proxy
-}

-- | Convert data to/from a 'BitVector'. This allows functions to be defined
Expand Down Expand Up @@ -478,7 +479,15 @@ instance ( BitPack a
) => BitPack (Either a b)

instance BitPack a => BitPack (Maybe a)
instance BitPack (Proxy a) => BitPack (Proxy a)

-- |
-- >>> pack (Proxy @())
-- 0
-- >>> pack (Proxy @5)
-- 0
-- >>> pack (Proxy @Bool)
-- 0
instance BitPack (Proxy a)

instance BitPack a => BitPack (Complex a)
instance BitPack a => BitPack (Down a)
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