panic: getIdFromTrivialExpr | Type families, generics, fundeps
This is on GHCi, version 8.6.5
, in the file WorkingGenerics.hs
*Main> :load WorkingGenerics
[1 of 1] Compiling WorkingGenerics ( /home/bollu/work/paper-deltas/src/WorkingGenerics.hs, interpreted )
ghc: panic! (the 'impossible' happened)
(GHC version 8.6.5 for x86_64-unknown-linux):
getIdFromTrivialExpr
(case a'_alGi of { })
`cast` (Sym (Nth:2
(Nth:3
(Inst (Sym (N:GDiff[0] (Rep_Void[0])) ; N:GDiff[0]
<Rep Void>_N) (Coh <Void>_N
(Sym (Nth:0
(Sym (N:GDiff[0]
(Rep_Void[0])) ; N:GDiff[0]
<Rep
Void>_N)))))))
:: Rep Void Void
~R# D1 ('MetaData "Void" "WorkingGenerics" "main" 'False) V1 Void)
Call stack:
CallStack (from HasCallStack):
callStackDoc, called at compiler/utils/Outputable.hs:1160:37 in ghc:Outputable
pprPanic, called at compiler/coreSyn/CoreUtils.hs:977:18 in ghc:CoreUtils
How to reproduce:
- Clone bollu/paper-deltas
- Run
stack ghci
- run
:load WorkingGenerics
inGHCi
I'm sorry, I have no idea how to reduce this kind of bug.