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Workaround ghc-typelits-extra#68 #185

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Workaround ghc-typelits-extra#68 #185

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9 changes: 7 additions & 2 deletions clash-protocols/src/Data/Constraint/Nat/Extra.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -17,8 +17,13 @@ leModulusDivisor :: forall a b. (1 <= b) => Dict (Mod a b + 1 <= b)
leModulusDivisor = unsafeCoerce (Dict :: Dict (0 <= 0))

-- | if (1 <= a) and (1 <= b) then (1 <= DivRU a b)
strictlyPositiveDivRu :: forall a b. (1 <= a, 1 <= b) => Dict (1 <= DivRU a b)
strictlyPositiveDivRu = unsafeCoerce (Dict :: Dict (0 <= 0))
strictlyPositiveDivRu ::
forall a b.
(1 <= a, 1 <= b) =>
-- | XXX: The 'Constraint' equality is there to work around
-- issue github.com/clash-lang/ghc-typelits-extra/issues/68.
Dict ((1 <= DivRU a b) ~ (() :: Constraint))
strictlyPositiveDivRu = unsafeCoerce (Dict :: Dict (() ~ ()))

-- | if (1 <= a) then (b <= ceil(b/a) * a)
leTimesDivRu :: forall a b. (1 <= a) => Dict (b <= a * DivRU b a)
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4 changes: 3 additions & 1 deletion clash-protocols/src/Protocols/PacketStream/Packetizers.hs
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Expand Up @@ -358,7 +358,9 @@ packetizeFromDfT ::
(KnownNat headerBytes) =>
(KnownNat dataWidth) =>
(1 <= dataWidth) =>
(1 <= headerBytes `DivRU` dataWidth) =>
-- \| XXX: The 'Constraint' equality is there to work around
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@rowanG077 rowanG077 Jan 7, 2026 •
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I think this will force users to have both ((1 <= headerBytes DivRU dataWidth) ~ (() :: Constraint)) which is confusing. I think it's probably better to have a constraintImpliesUnitConstraint :: forall a. a => Dict (a ~ (() :: Constraint)) and apply that.

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@martijnbastiaan martijnbastiaan Jan 7, 2026

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Alright, makes sense to me

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@martijnbastiaan martijnbastiaan Jan 7, 2026

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I talked to Christiaan in the office btw, hence skipping the review. Glad you caught it though.

-- issue github.com/clash-lang/ghc-typelits-extra/issues/68.
((1 <= headerBytes `DivRU` dataWidth) ~ (() :: Constraint)) =>
((dataWidth + 1) <= headerBytes) =>
-- | Mapping from `Df` input to output `_meta`
(a -> metaOut) ->
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