help understanding a ghc assert failure wrt coercions
Ben Gamari
ben at smart-cactus.org
Mon Jan 6 04:44:13 UTC 2020
On January 5, 2020 10:11:30 PM EST, Carter Schonwald <carter.schonwald at gmail.com> wrote:
>Hey all,
>I've been spending a little bit of time hacking out my own little
>"erase
>coercions"
>branch, and with asserts enabled i'm seeing a very strange panic that
>seems
>to be invalid?
>namely: its stating that the types have changed,
>
>BUT the error output indicates that the types are the same on both
>sides!
>
>
>
>ghc: panic! (the 'impossible' happened)
> (GHC version 8.11.0.20200106:
>ASSERT failed!
> optCoercion changed types!
> in_co:
> Univ(representational Erased
> :: IO a_a2Pd, State# RealWorld -> (# State# RealWorld, a_a2Pd #))
> in_ty1: IO a_a2Pd
> in_ty2: State# RealWorld -> (# State# RealWorld, a_a2Pd #)
> out_co:
> Univ(representational Erased
> :: IO a_a2Pd, State# RealWorld -> (# State# RealWorld, a_a2Pd #))
> out_ty1: IO a_a2Pd
> out_ty2: State# RealWorld -> (# State# RealWorld, a_a2Pd #)
> subst:
> [TCvSubst
> In scope: InScope {wild_00 augment ++ build foldr eqString bindIO
> returnIO otherwise assert thenIO breakpoint
>breakpointCond map $
> join f_a19W x_a19X x_a1hI s_a1hZ $c==_a2rD
>$c/=_a2rM $cp1Ord_a2rY
> $ccompare_a2s0 $c<_a2se $c<=_a2ss $c>_a2sy
>$c>=_a2sE $cmax_a2sL
> $cmin_a2sS $cp1Monoid_a2t4 $cmappend_a2tf
>$cmconcat_a2tl $c>>=_a2tD
> $c>>_a2tS $creturn_a2u3 $cpure_a2uo $c<*>_a2uA
>$cliftA2_a2uN
> $c*>_a2v0 $c<*_a2vb $c>>=_a2vw $c>>_a2vJ
>$creturn_a2vU $cpure_a2wd
> $c<*>_a2wn $cliftA2_a2wy $c*>_a2wL $c<*_a2wW
>$c>>=_a2xf $c>>_a2xq
> $creturn_a2xB $c<*>_a2y0 $cliftA2_a2y9 $c*>_a2yj
>$c<*_a2yu
> $cmappend_a2yS $cmconcat_a2yY $cmappend_a2ze
>$cmconcat_a2zk
> $cp1Monoid_a2zE $cmempty_a2zG $cmappend_a2zU
>$cmconcat_a2A0
> $cp1Monoid_a2Ai $cmempty_a2Ak $cmappend_a2Aw
>$cmconcat_a2AC
> $cp1Monoid_a2AS $cmempty_a2AU $cmappend_a2B4
>$cmconcat_a2Ba
> $cp1Monoid_a2Bo $cmempty_a2Bq $cmappend_a2By
>$cmconcat_a2BE
> $cmappend_a2BU $cmconcat_a2C0 $cp1Monoid_a2Cb
>$cmappend_a2Cj
> $cmconcat_a2Cp $cmappend_a2CH $cmconcat_a2CN
>$c<>_a2CX
> $csconcat_a2D8 $cstimes_a2De $c<>_a2Dt
>$csconcat_a2DA $c<>_a2DV
> $csconcat_a2DZ $cstimes_a2E5 $c<>_a2Eu
>$csconcat_a2EI $cstimes_a2EO
> $c<>_a2Fp $csconcat_a2FB $cstimes_a2FH $c<>_a2Gc
>$csconcat_a2Gm
> $cstimes_a2Gs $c<>_a2GR $csconcat_a2GZ
>$cstimes_a2H5 $c<>_a2Hm
> $csconcat_a2Hq $cstimes_a2Hu $c<>_a2HG
>$csconcat_a2HM $cstimes_a2HS
> $c<>_a2I6 $csconcat_a2Id $cstimes_a2Ij
>$csconcat_a2IC $cstimes_a2II
> $c>>=_a2J0 $c>>_a2JO $creturn_a2JZ $cpure_a2Ke
>$c<*>_a2Kl
> $cliftA2_a2Kw $c*>_a2KJ $c<*_a2KU $cfmap_a2L7
>$c<$_a2Lj
> $cmzero_a2LF $cmplus_a2LO $cmzero_a2M7
>$cmplus_a2Mg $cmzero_a2Mz
> $cmplus_a2MI $csome_a2Na $cmany_a2Nj $csome_a2NK
>$cmany_a2NT
> $c<|>_a2Oe $csome_a2Oj $cmany_a2Os $c>>_a2OP
>$creturn_a2P0
> $cfmap_a2Pb $c<$_a2Ps a_a2Pu b_a2Pv $c>>=_a2PJ
>$creturn_a2Q2
> $c>>=_a2Qh $creturn_a2Qz $c>>=_a2QP $c>>_a2QV
>$creturn_a2R6
> $c<*>_a2Rr $cliftA2_a2RC $c<*_a2RX $cpure_a2Se
>$c<*>_a2Sj
> $cliftA2_a2Sr $c*>_a2SA $c<*_a2SI $c<*>_a2T5
>$cliftA2_a2Th
> $c*>_a2Tq $c<*_a2Tx $c<*>_a2TW $cliftA2_a2U2
>$c*>_a2U9 $c<*_a2Uk
> $c<$_a2UF $cfmap_a2US $c<$_a2V0 $cfmap_a2Ve
>$c<$_a2Vk $c<$_a2VH
> $cfmap_a2VX $c<$_a2W3 $cfmap_a2Wi $c<$_a2Wo
>$krep_a37a $krep_a37b
> $krep_a37c $krep_a37d $krep_a37e $krep_a37f
>$krep_a37g $krep_a37h
> $krep_a37i $krep_a37j $krep_a37k $krep_a37l
>$krep_a37m $krep_a37n
> $krep_a37o $krep_a37p $krep_a37q $krep_a37r
>$krep_a37s $sap_d3dm
> $sap_d3dn $sliftM5_d3ds $sliftM5_d3dt
>$sliftM4_d3dy $sliftM4_d3dz
> $sliftM3_d3dE $sliftM3_d3dF $sliftM2_d3dK
>$sliftM2_d3dL
> $sliftM_d3dQ $sliftM_d3dR $swhen_d3e3 $swhen_d3e4
>$s=<<_d3e9
> $sliftA3_d3eh $sliftA3_d3ei $sliftA_d3em
>$sliftA_d3en $tcMonoid
> $tcSemigroup $trModule <**> liftA liftA3 =<< when
>sequence mapM
> liftM liftM2 liftM3 liftM4 liftM5 ap mapFB
>unsafeChr ord minInt
> maxInt id const . flip $! until asTypeOf failIO
>unIO getTag quotInt
> remInt divInt modInt quotRemInt divModInt
>divModInt# shiftL#
> shiftRL# iShiftL# iShiftRA# iShiftRL# $tcFunctor
>$dm<$ $fFunctor[]
> $fFunctorMaybe $fFunctor(,) $fFunctor->
>$fFunctor(,,,)
> $fFunctor(,,) $tcApplicative $dm<*> $dmliftA2
>$dm*> $dm<*
> $fApplicativeIO $fApplicative[]
>$fApplicativeMaybe $fApplicative->
> $tcMonad $dm>> $dmreturn $fMonadIO $fFunctorIO
>$fMonad[]
> $fMonadMaybe $fMonad-> $tcAlternative $dmsome
>$dmmany
> $fAlternativeIO $fAlternative[]
>$fAlternativeMaybe $tcMonadPlus
> $dmmzero $dmmplus $fMonadPlusIO $fMonadPlus[]
>$fMonadPlusMaybe
> $tc':| $tcNonEmpty $fMonadNonEmpty
>$fApplicativeNonEmpty
> $fFunctorNonEmpty $dmsconcat $dmstimes
>$fSemigroupIO
> $fSemigroupMaybe $fSemigroupOrdering
>$fSemigroup(,,,,)
> $fSemigroup(,,,) $fSemigroup(,,) $fSemigroup(,)
>$fSemigroup()
> $fSemigroup-> $fSemigroupNonEmpty $fSemigroup[]
>$dmmappend
> $dmmconcat $tc'C:Monoid $fMonoidIO $fMonad(,,,)
>$fApplicative(,,,)
> $fMonad(,,) $fApplicative(,,) $fMonad(,)
>$fApplicative(,)
> $fMonoidMaybe $fMonoidOrdering $fMonoid(,,,,)
>$fMonoid(,,,)
> $fMonoid(,,) $fMonoid(,) $fMonoid() $fMonoid->
>$fMonoid[] $tc'O
> $tcOpaque $fEqNonEmpty $fOrdNonEmpty
>returnIO_s3A8 failIO_s3A9
> $cempty_s3Ab unIO_s3Ac thenIO_s3Ah bindIO_s3Am
>$trModule_s3AL
> $trModule_s3AM $trModule_s3AN $trModule_s3AO
>$krep_s3AP
> $tcFunctor_s3AQ $tcFunctor_s3AR
>$tcApplicative_s3AS
> $tcApplicative_s3AT $tcMonad_s3AU $tcMonad_s3AV
>$tcAlternative_s3AW
> $tcAlternative_s3AX $tcMonadPlus_s3AY
>$tcMonadPlus_s3AZ
> $tcNonEmpty_s3B0 $tcNonEmpty_s3B1 $krep_s3B2
>$tc':|_s3B3
> $tc':|_s3B4 $tcSemigroup_s3B5 $tcSemigroup_s3B6
>$krep_s3B7
> $tcMonoid_s3B8 $tcMonoid_s3B9 $krep_s3Ba
>$tc'C:Monoid_s3Bb
> $tc'C:Monoid_s3Bc $tcOpaque_s3Bd $tcOpaque_s3Be
>$tc'O_s3Bf
> $tc'O_s3Bg $cliftA2_s3BL $cfmap_s3BP $c<*>_s3BT
>$sap_s3BW
> $sliftM2_s3BZ $sliftM5_s3Cc $sliftM4_s3Ch
>$sliftM3_s3Cl
> $sliftM_s3Co f_s3FS}
> Type env: [a2Pd :-> b_a2Pv, a2Pe :-> a_a2Pu]
> Co env: []]
> Call stack:
> CallStack (from HasCallStack):
> callStackDoc, called at compiler/utils/Outputable.hs:1173:37 in
>ghc:Outputable
> pprPanic, called at compiler/utils/Outputable.hs:1243:5 in
>ghc:Outputable
> assertPprPanic, called at compiler/types/OptCoercion.hs:122:41 in
>ghc:OptCoercion
Try adding -dppr-debug to your command line. This may reveal the difference.
Cheers,
- Ben
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