Instantiation variables leak to the constraint solver.
The test where this happens: .typechecker/test/cases/should-typecheck/break-infer.hs
Error:
[PprPanic]
Instantiation variable in the constraint solver:
mu48:Type
CallStack (from HasCallStack):
pprPanic, called at src/Tc/Solver/Equality.hs:78:5 in typechecker-0.1.0.0-inplace:Tc.Solver.EqualityWanted constraints:
[W] Type ~ Type
[W] Type ~ Type
[W] List mv-t37[0]:Type ~ List mv-t37[0]:Type
[W] List mv-t37[0]:Type ~ List mv-t37[0]:Type
[W] mv-t36[0]:Type ~ mv-t40[0]:Type
[W] List mv-t37[0]:Type ~ List mv-t41[0]:Type
[W] mv-t40[0]:Type ~ (mv-t42[0]:Type -> mv-t43[0]:Type)
[W] mv-t42[0]:Type ~ mv-t41[0]:Type
[W] mv-t43[0]:Type ~ Bool
[W] Type ~ Type
[W] Tuple2 List mv-t37[0]:Type List mv-t37[0]:Type ~ Tuple2 mv-t47[0]:Type List mv-t41[0]:Type
[W] mv-t47[0]:Type ~ List mu48:Type
[W] List mv-t41[0]:Type ~ List mv-t41[0]:Type
[W] Type ~ Type
[W] Type ~ Type
[W] Tuple2 mv-t47[0]:Type List mv-t41[0]:Type ~ Tuple2 List mv-t41[0]:Type mv-t83[0]:Type
[W] Type ~ Type
[W] List mv-t41[0]:Type ~ List mv-t41[0]:Type
[W] mv-t41[0]:Type ~ mv-t41[0]:Type
[W] Type ~ Type
[W] List mv-t41[0]:Type ~ List mv-t41[0]:Type
[W] Type ~ Type
[W] mv-t83[0]:Type ~ mv-t83[0]:Type