    {-# LANGUAGE Trustworthy #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  GHC.Stack
    -- Copyright   :  (c) The University of Glasgow 2011
    -- License     :  see libraries/base/LICENSE
    --
    -- Maintainer  :  cvs-ghc@haskell.org
    -- Stability   :  internal
    -- Portability :  non-portable (GHC Extensions)
    --
    -- Access to GHC's call-stack simulation
    --
    -- @since 4.5.0.0
    -----------------------------------------------------------------------------

    {-# LANGUAGE MagicHash, NoImplicitPrelude, ImplicitParams, RankNTypes #-}
    module GHC.Stack (
        errorWithStackTrace,

        -- * Profiling call stacks
        currentCallStack,
        whoCreated,

        -- * HasCallStack call stacks
        CallStack, HasCallStack, callStack, emptyCallStack, freezeCallStack,
        fromCallSiteList, getCallStack, popCallStack, prettyCallStack,
        pushCallStack, withFrozenCallStack,

        -- * Source locations
        SrcLoc(..), prettySrcLoc,

        -- * Internals
        CostCentreStack,
        CostCentre,
        getCurrentCCS,
        getCCSOf,
        clearCCS,
        ccsCC,
        ccsParent,
        ccLabel,
        ccModule,
        ccSrcSpan,
        ccsToStrings,
        renderStack
      ) where

    import GHC.Stack.CCS
    import GHC.Stack.Types
    import GHC.IO
    import GHC.Base
    import GHC.List
    import GHC.Exception

    -- | Like the function 'error', but appends a stack trace to the error
    -- message if one is available.
    --
    -- @since 4.7.0.0
    {-# DEPRECATED errorWithStackTrace "'error' appends the call stack now" #-}
      -- DEPRECATED in 8.0.1
    errorWithStackTrace :: String -> a
    errorWithStackTrace x = unsafeDupablePerformIO $ do
       stack <- ccsToStrings =<< getCurrentCCS x
       if null stack
          then throwIO (ErrorCall x)
          else throwIO (ErrorCallWithLocation x (renderStack stack))

    -- | Pop the most recent call-site off the 'CallStack'.
    --
    -- This function, like 'pushCallStack', has no effect on a frozen 'CallStack'.
    --
    -- @since 4.9.0.0
    popCallStack :: CallStack -> CallStack
    popCallStack stk = case stk of
      EmptyCallStack         -> errorWithoutStackTrace "popCallStack: empty stack"
      PushCallStack _ _ stk' -> stk'
      FreezeCallStack _      -> stk
    {-# INLINE popCallStack #-}

    -- | Return the current 'CallStack'.
    --
    -- Does *not* include the call-site of 'callStack'.
    --
    -- @since 4.9.0.0
    callStack :: HasCallStack => CallStack
    callStack = popCallStack ?callStack
    {-# INLINE callStack #-}

    -- | Perform some computation without adding new entries to the 'CallStack'.
    --
    -- @since 4.9.0.0
    withFrozenCallStack :: HasCallStack
                        => ( HasCallStack => a )
                        -> a
    withFrozenCallStack do_this =
      -- we pop the stack before freezing it to remove
      -- withFrozenCallStack's call-site
      let ?callStack = freezeCallStack (popCallStack callStack)
      in do_this