#12734: Unexpected context reduction stack overflow -------------------------------------+------------------------------------- Reporter: danilo2 | Owner: Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Hello! I don't have a minimal example, but I've got a very clear strange bahavior: We've got a function: {{{ nstar3 :: ( ExprCons t layers m, Bindable t m, Self.MonadSelfBuilder (Binding (Expr2 t layers AnyLayout)) m , ExprInferable t layers m) => m (Binding (PrimExpr2' t layers Star)) nstar3 = Self.put . anyLayout2 =<<& (nstar2 >>= mkBinding) }}} If I use it in a different function and use following explicit type, I get the error: {{{ test_gr3 :: ( ExprCons t layers m, Bindable t m, ExprInferable t layers m , MonadIO m, Show bind, Show (PrimExpr2' t layers Star), layers~'[Data, Type] , Self.MonadSelfBuilder (Binding (Expr2 t layers AnyLayout)) m , bind ~ Binding (PrimExpr2' t layers Star) ) => m bind test_gr3 = do sref <- nstar3 }}} error (while using the function and evaluating monads): {{{ • Reduction stack overflow; size = 201 When simplifying the following type: MonadFix (Self.SelfBuilderT (Binding (Expr2 t0 '[Data, Type] AnyLayout)) m) Use -freduction-depth=0 to disable this check (any upper bound you could choose might fail unpredictably with minor updates to GHC, so disabling the check is recommended if you're sure that type checking should terminate) • In the second argument of ‘($)’, namely ‘(test_gr3)’ In the second argument of ‘($)’, namely ‘runInferenceT2 @TermType @Net $ (test_gr3)’ In the second argument of ‘($)’, namely ‘runInferenceT2 @InfLayers @'[Data, Type] $ runInferenceT2 @TermType @Net $ (test_gr3)’ }}} What is "funny" is that if I change the type of `test_gr3` to a very similar one, I just replace the part `=> m bind` with manually expanded one `m (Binding (PrimExpr2' t layers Star))` everything compiles fine. It would be really hard to get minimal example out of it – it uses nested mfixes and will take much time to cut it down. The question is – can we locate the error based on the description? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12734 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler