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Expressions remains recursive after normalization #5

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Expressions remains recursive after normalization#5

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@TristanCacqueray
TristanCacqueray
opened on Jan 17, 2026

Hello,

when trying to build tinybasic with ghc-9.6.7 and clash-1.8.4, verilog synthesis fails with the following error:

$ clashi src/intel8080/video-board.hs -isrc
Clashi, version 1.8.4 (using clash-lib, version 1.8.4):
clashi> :verilog
Clash: Compiling Main.topEntity
Clash.Normalize(187): Expr belonging to bndr: c$Data.Monoid.$fMonoidAp_$cmconcat_go1[393088] (:: GHC.Types.List[3674937295934324788]
  (Data.Monoid.Ap[8214565720323893074]
     (GHC.Prim.TYPE[3674937295934324918]
        (GHC.Types.BoxedRep[3891110078048108766]
           GHC.Types.Lifted[3891110078048108808]))
     (Clash.Signal.Internal.Signal[8214565720323892722] "Dom25")
     (GHC.Maybe.Maybe[3674937295934324792]
        (Clash.Sized.Internal.BitVector.BitVector[8214565720323892754]
           8)))
-> Data.Monoid.Ap[8214565720323893074]
     (GHC.Prim.TYPE[3674937295934324918]
        (GHC.Types.BoxedRep[3891110078048108766]
           GHC.Types.Lifted[3891110078048108808]))
     (Clash.Signal.Internal.Signal[8214565720323892722] "Dom25")
     (GHC.Maybe.Maybe[3674937295934324792]
        (Clash.Sized.Internal.BitVector.BitVector[8214565720323892754]
           8))) remains recursive after normalization:
λ(ds[8214565720324003356] :: GHC.Types.List[3674937295934324788]
                               (Data.Monoid.Ap[8214565720323893074]
                                  (GHC.Prim.TYPE[3674937295934324918]
                                     (GHC.Types.BoxedRep[3891110078048108766]
                                        GHC.Types.Lifted[3891110078048108808]))
                                  (Clash.Signal.Internal.Signal[8214565720323892722] "Dom25")
                                  (GHC.Maybe.Maybe[3674937295934324792]
                                     (Clash.Sized.Internal.BitVector.BitVector[8214565720323892754]
                                        8)))) ->
letrec
  result[397188] :: GHC.Maybe.Maybe[3674937295934324792]
                      (Clash.Sized.Internal.BitVector.BitVector[8214565720323892754]
                         8)
  = <prefixName>"liftA2"
  <prefixName>"$fApplicativeSignal"
  <prefixName>"$fApplicativeSignal_$cliftA2"
  <prefixName>"<>"
  <prefixName>"muxA_v1"
  <prefixName>"$fMonoidAlt"
  <prefixName>"$fSemigroupAlt"
  <prefixName>"<|>"
  <prefixName>"$fAlternativeMaybe"
  <prefixName>"$fAlternativeMaybe_$c<|>"
  case y[8214565720324003359][LocalId] of
    GHC.Maybe.Nothing[3891110078048108565]  ->
      eta2[8214565720324020536][LocalId]
    GHC.Maybe.Just[3891110078048108568]
      (ipv[8214565720324020882] :: Clash.Sized.Internal.BitVector.BitVector[8214565720323892754]
                                     8) ->
      y[8214565720324003359][LocalId]
  y[8214565720324003359] :: Data.Monoid.Ap[8214565720323893074]
                              (GHC.Prim.TYPE[3674937295934324918]
                                 (GHC.Types.BoxedRep[3891110078048108766]
                                    GHC.Types.Lifted[3891110078048108808]))
                              (Clash.Signal.Internal.Signal[8214565720323892722] "Dom25")
                              (GHC.Maybe.Maybe[3674937295934324792]
                                 (Clash.Sized.Internal.BitVector.BitVector[8214565720323892754]
                                    8))
  = case ds[8214565720324003356][LocalId] of
      GHC.Types.:[3891110078048108550]
        (c$sel[397191] :: Data.Monoid.Ap[8214565720323893074]
                            (GHC.Prim.TYPE[3674937295934324918]
                               (GHC.Types.BoxedRep[3891110078048108766]
                                  GHC.Types.Lifted[3891110078048108808]))
                            (Clash.Signal.Internal.Signal[8214565720323892722] "Dom25")
                            (GHC.Maybe.Maybe[3674937295934324792]
                               (Clash.Sized.Internal.BitVector.BitVector[8214565720323892754]
                                  8)))
          (c$wild[397190] :: GHC.Types.List[3674937295934324788]
                               (Data.Monoid.Ap[8214565720323893074]
                                  (GHC.Prim.TYPE[3674937295934324918]
                                     (GHC.Types.BoxedRep[3891110078048108766]
                                        GHC.Types.Lifted[3891110078048108808]))
                                  (Clash.Signal.Internal.Signal[8214565720323892722] "Dom25")
                                  (GHC.Maybe.Maybe[3674937295934324792]
                                     (Clash.Sized.Internal.BitVector.BitVector[8214565720323892754]
                                        8)))) ->
        c$sel[397191][LocalId]
  ys[8214565720324003360] :: GHC.Types.List[3674937295934324788]
                               (Data.Monoid.Ap[8214565720323893074]
                                  (GHC.Prim.TYPE[3674937295934324918]
                                     (GHC.Types.BoxedRep[3891110078048108766]
                                        GHC.Types.Lifted[3891110078048108808]))
                                  (Clash.Signal.Internal.Signal[8214565720323892722] "Dom25")
                                  (GHC.Maybe.Maybe[3674937295934324792]
                                     (Clash.Sized.Internal.BitVector.BitVector[8214565720323892754]
                                        8)))
  = case ds[8214565720324003356][LocalId] of
      GHC.Types.:[3891110078048108550]
        (c$wild[397192] :: Data.Monoid.Ap[8214565720323893074]
                             (GHC.Prim.TYPE[3674937295934324918]
                                (GHC.Types.BoxedRep[3891110078048108766]
                                   GHC.Types.Lifted[3891110078048108808]))
                             (Clash.Signal.Internal.Signal[8214565720323892722] "Dom25")
                             (GHC.Maybe.Maybe[3674937295934324792]
                                (Clash.Sized.Internal.BitVector.BitVector[8214565720323892754]
                                   8)))
          (c$sel[397194] :: GHC.Types.List[3674937295934324788]
                              (Data.Monoid.Ap[8214565720323893074]
                                 (GHC.Prim.TYPE[3674937295934324918]
                                    (GHC.Types.BoxedRep[3891110078048108766]
                                       GHC.Types.Lifted[3891110078048108808]))
                                 (Clash.Signal.Internal.Signal[8214565720323892722] "Dom25")
                                 (GHC.Maybe.Maybe[3674937295934324792]
                                    (Clash.Sized.Internal.BitVector.BitVector[8214565720323892754]
                                       8)))) ->
        c$sel[397194][LocalId]
  eta2[8214565720324020536] :: Data.Monoid.Ap[8214565720323893074]
                                 (GHC.Prim.TYPE[3674937295934324918]
                                    (GHC.Types.BoxedRep[3891110078048108766]
                                       GHC.Types.Lifted[3891110078048108808]))
                                 (Clash.Signal.Internal.Signal[8214565720323892722] "Dom25")
                                 (GHC.Maybe.Maybe[3674937295934324792]
                                    (Clash.Sized.Internal.BitVector.BitVector[8214565720323892754]
                                       8))
  = c$Data.Monoid.$fMonoidAp_$cmconcat_go1[393088][GlobalId]
      ys[8214565720324003360][LocalId]
  result[397195] :: Data.Monoid.Ap[8214565720323893074]
                      (GHC.Prim.TYPE[3674937295934324918]
                         (GHC.Types.BoxedRep[3891110078048108766]
                            GHC.Types.Lifted[3891110078048108808]))
                      (Clash.Signal.Internal.Signal[8214565720323892722] "Dom25")
                      (GHC.Maybe.Maybe[3674937295934324792]
                         (Clash.Sized.Internal.BitVector.BitVector[8214565720323892754]
                            8))
  = case ds[8214565720324003356][LocalId] of
      GHC.Types.[][3891110078048108574]  ->
        <prefixName>"pure"
        <prefixName>"$fApplicativeSignal"
        <prefixName>"mempty"
        <prefixName>"muxA_v1"
        <prefixName>"$fMonoidAlt"
        <prefixName>"empty"
        <prefixName>"$fAlternativeMaybe"
          GHC.Maybe.Nothing[3891110078048108565]
          @(Clash.Sized.Internal.BitVector.BitVector[8214565720323892754]
              8)
      GHC.Types.:[3891110078048108550]
        (y[8214565720324003359] :: Data.Monoid.Ap[8214565720323893074]
                                     (GHC.Prim.TYPE[3674937295934324918]
                                        (GHC.Types.BoxedRep[3891110078048108766]
                                           GHC.Types.Lifted[3891110078048108808]))
                                     (Clash.Signal.Internal.Signal[8214565720323892722] "Dom25")
                                     (GHC.Maybe.Maybe[3674937295934324792]
                                        (Clash.Sized.Internal.BitVector.BitVector[8214565720323892754]
                                           8)))
          (ys[8214565720324003360] :: GHC.Types.List[3674937295934324788]
                                        (Data.Monoid.Ap[8214565720323893074]
                                           (GHC.Prim.TYPE[3674937295934324918]
                                              (GHC.Types.BoxedRep[3891110078048108766]
                                                 GHC.Types.Lifted[3891110078048108808]))
                                           (Clash.Signal.Internal.Signal[8214565720323892722] "Dom25")
                                           (GHC.Maybe.Maybe[3674937295934324792]
                                              (Clash.Sized.Internal.BitVector.BitVector[8214565720323892754]
                                                 8)))) ->
        result[397188][LocalId]
in result[397195][LocalId]

It looks like the issue comes from RetroClash.Utils.shifterL, and using this implementation fixes the recursion:

shifterL' ::
    (BitPack a, HiddenClockResetEnable dom) =>
    Signal dom (Maybe a) ->
    Signal dom Bool ->
    Signal dom Bit
shifterL' load tick = msb <$> next
  where
    r = register 0 next

    initial = fmap pack <$> load
    shifted = (`shiftL` 1) <$> r
    next = muxA (initial :> enable tick shifted :> Nil) .<|. r

… that way:

diff --git a/src/Hardware/TinyBASIC/Video.hs b/src/Hardware/TinyBASIC/Video.hs
index b20e59c..2f6077a 100644
--- a/src/Hardware/TinyBASIC/Video.hs
+++ b/src/Hardware/TinyBASIC/Video.hs
@@ -90,7 +90,7 @@ video (fromSignal -> cursor) (fromSignal -> w) = (frameEnd, delayVGA vgaSync rgb
: 
 
     glyphLoad = enable (delayI False newChar) $ fontRom charLoad (fromMaybe 0 <$> delayI Nothing (fromSignal glyphY))
     newCol = delayI False $ fromSignal $ changed Nothing glyphX
-    pixel = enable (delayI False visible) $ liftD2 shifterL glyphLoad newCol
+    pixel = enable (delayI False visible) $ liftD2 shifterL' glyphLoad newCol

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