#10166: GHCi: internal error: stg_ap_p_ret -------------------------------------+------------------------------------- Reporter: | Owner: andreas.abel | Status: new Type: bug | Milestone: Priority: normal | Version: 7.8.4 Component: GHCi | Operating System: Unknown/Multiple Keywords: | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- {{{#!hs import Unsafe.Coerce coerce = Unsafe.Coerce.unsafeCoerce data Nat = Zero | Suc Nat fromNat :: Nat -> Integer fromNat Zero = 0 fromNat (Suc l) = 1 + fromNat l instance Show Nat where show l = show (fromNat l) data Exp = Const Nat | Pred | App Exp Exp eval :: Exp -> a eval (Const n) = coerce n eval e = coerce $ evalP e where evalP Pred Zero = Zero evalP Pred (Suc n) = n evalP e n = evalA e n evalA (App f e) = eval f (eval e) evalA _ = error "eval" -- With type signature, result is 0 (wrong, should be 1) -- Without type signature: internal error: stg_ap_p_ret -- test :: Nat test = eval $ App Pred $ Const $ Suc $ Suc Zero -- main prints 0 should maybe print 1 main :: IO () main = print (coerce test :: Nat) }}} when evaluatiing test at the ghci prompt after loading, I get {{{ <interactive>: internal error: stg_ap_p_ret (GHC version 7.8.3 for x86_64_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Process haskell aborted (core dumped) }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10166 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler