topEntity synthesis fails due to insufficient type-level normalisation

[gergoerdi]

CLaSH 0.99.3 chokes on the following source file:

import Clash.Prelude

topEntity
    :: (dom ~ System)
    => Clock dom Source
    -> Signal dom Bit
    -> Signal dom Bit
topEntity = exposeClock board
  where
    board = id

with the following error message:

*** Exception: Clash.Normalize(380): Can't translate domain: dom

Manually inlining System for dom everywhere is an effective workaround.

[christiaanb]

So the issue is that this still has a big lambda in the Core:

Main.topEntity8214565720325262584 before normalization:

Λdom ->
λ($d~ :: Data.Type.Equality.~
           Clash.Signal.Internal.Domain
           dom
           (Clash.Signal.Internal.Dom system 10000)) ->
λ(eta :: Clash.Signal.Internal.Clock
           dom
           Clash.Signal.Internal.Source) ->
λ(eta1 :: Clash.Signal.Internal.Signal
            dom
            Clash.Sized.Internal.BitVector.Bit) ->
case GHC.Types.HEq_sc3458764513820541480
       @Clash.Signal.Internal.Domain
       @Clash.Signal.Internal.Domain
       @dom
       @(Clash.Signal.Internal.Dom system 10000)
       $d~ of
  _ ->
    eta1

Clash is sorta expecting for topEntity not to have any big-lambda's at all; so fixing this issue is somewhat non-trivial.

As a work-around you could just use:

type SignalS a = Signal System a

for now.