Copyright	(c) The University of Glasgow 2011
License	see libraries/base/LICENSE
Maintainer	cvs-ghc@haskell.org
Stability	internal
Portability	non-portable (GHC Extensions)
Safe Haskell	Trustworthy
Language	Haskell2010

GHC.Stack

Contents

Profiling call stacks
HasCallStack call stacks
Source locations
Internals

Description

Access to GHC's call-stack simulation

Since: base-4.5.0.0

Synopsis

errorWithStackTrace :: String -> a
currentCallStack :: IO [String]
whoCreated :: a -> IO [String]
data CallStack
type HasCallStack = ?callStack :: CallStack
callStack :: HasCallStack => CallStack
emptyCallStack :: CallStack
freezeCallStack :: CallStack -> CallStack
fromCallSiteList :: [([Char], SrcLoc)] -> CallStack
getCallStack :: CallStack -> [([Char], SrcLoc)]
popCallStack :: CallStack -> CallStack
prettyCallStack :: CallStack -> String
pushCallStack :: ([Char], SrcLoc) -> CallStack -> CallStack
withFrozenCallStack :: HasCallStack => (HasCallStack => a) -> a
data SrcLoc = SrcLoc {
- srcLocPackage :: [Char]
- srcLocModule :: [Char]
- srcLocFile :: [Char]
- srcLocStartLine :: Int
- srcLocStartCol :: Int
- srcLocEndLine :: Int
- srcLocEndCol :: Int
}
prettySrcLoc :: SrcLoc -> String
data CostCentreStack
data CostCentre
getCurrentCCS :: dummy -> IO (Ptr CostCentreStack)
getCCSOf :: a -> IO (Ptr CostCentreStack)
clearCCS :: IO a -> IO a
ccsCC :: Ptr CostCentreStack -> IO (Ptr CostCentre)
ccsParent :: Ptr CostCentreStack -> IO (Ptr CostCentreStack)
ccLabel :: Ptr CostCentre -> IO CString
ccModule :: Ptr CostCentre -> IO CString
ccSrcSpan :: Ptr CostCentre -> IO CString
ccsToStrings :: Ptr CostCentreStack -> IO [String]
renderStack :: [String] -> String

Documentation

errorWithStackTrace :: String -> a #

Deprecated: error appends the call stack now

Like the function error, but appends a stack trace to the error message if one is available.

Since: base-4.7.0.0

Profiling call stacks

currentCallStack :: IO [String] #

Returns a [String] representing the current call stack. This can be useful for debugging.

The implementation uses the call-stack simulation maintained by the profiler, so it only works if the program was compiled with -prof and contains suitable SCC annotations (e.g. by using -fprof-auto). Otherwise, the list returned is likely to be empty or uninformative.

Since: base-4.5.0.0

whoCreated :: a -> IO [String] #

Get the stack trace attached to an object.

Since: base-4.5.0.0

HasCallStack call stacks

data CallStack #

CallStacks are a lightweight method of obtaining a partial call-stack at any point in the program.

A function can request its call-site with the HasCallStack constraint. For example, we can define

putStrLnWithCallStack :: HasCallStack => String -> IO ()

as a variant of putStrLn that will get its call-site and print it, along with the string given as argument. We can access the call-stack inside putStrLnWithCallStack with callStack.

putStrLnWithCallStack :: HasCallStack => String -> IO ()
putStrLnWithCallStack msg = do
  putStrLn msg
  putStrLn (prettyCallStack callStack)

Thus, if we call putStrLnWithCallStack we will get a formatted call-stack alongside our string.

>>> putStrLnWithCallStack "hello"
hello
CallStack (from HasCallStack):
  putStrLnWithCallStack, called at <interactive>:2:1 in interactive:Ghci1

GHC solves HasCallStack constraints in three steps:

If there is a CallStack in scope -- i.e. the enclosing function has a HasCallStack constraint -- GHC will append the new call-site to the existing CallStack.
If there is no CallStack in scope -- e.g. in the GHCi session above -- and the enclosing definition does not have an explicit type signature, GHC will infer a HasCallStack constraint for the enclosing definition (subject to the monomorphism restriction).
If there is no CallStack in scope and the enclosing definition has an explicit type signature, GHC will solve the HasCallStack constraint for the singleton CallStack containing just the current call-site.

CallStacks do not interact with the RTS and do not require compilation with -prof. On the other hand, as they are built up explicitly via the HasCallStack constraints, they will generally not contain as much information as the simulated call-stacks maintained by the RTS.

A CallStack is a [(String, SrcLoc)]. The String is the name of function that was called, the SrcLoc is the call-site. The list is ordered with the most recently called function at the head.

NOTE: The intrepid user may notice that HasCallStack is just an alias for an implicit parameter ?callStack :: CallStack. This is an implementation detail and should not be considered part of the CallStack API, we may decide to change the implementation in the future.

Since: base-4.8.1.0

Instances

IsList CallStack #	Be aware that 'fromList . toList = id' only for unfrozen `CallStack`s, since `toList` removes frozenness information. Since: base-4.9.0.0
Instance details Defined in GHC.Exts Associated Types type Item CallStack :: Type # Methods fromList :: [Item CallStack] -> CallStack # fromListN :: Int -> [Item CallStack] -> CallStack # toList :: CallStack -> [Item CallStack] #
Show CallStack #	Since: base-4.9.0.0
Instance details Defined in GHC.Show Methods showsPrec :: Int -> CallStack -> ShowS # show :: CallStack -> String # showList :: [CallStack] -> ShowS #
type Item CallStack #
Instance details Defined in GHC.Exts type Item CallStack = (String, SrcLoc)

type HasCallStack = ?callStack :: CallStack #

Request a CallStack.

NOTE: The implicit parameter ?callStack :: CallStack is an implementation detail and should not be considered part of the CallStack API, we may decide to change the implementation in the future.

Since: base-4.9.0.0

callStack :: HasCallStack => CallStack #

Return the current CallStack.

Does *not* include the call-site of callStack.

Since: base-4.9.0.0

emptyCallStack :: CallStack #

The empty CallStack.

Since: base-4.9.0.0

freezeCallStack :: CallStack -> CallStack #

Freeze a call-stack, preventing any further call-sites from being appended.

pushCallStack callSite (freezeCallStack callStack) = freezeCallStack callStack

Since: base-4.9.0.0

fromCallSiteList :: [([Char], SrcLoc)] -> CallStack #

Convert a list of call-sites to a CallStack.

Since: base-4.9.0.0

getCallStack :: CallStack -> [([Char], SrcLoc)] #

Extract a list of call-sites from the CallStack.

The list is ordered by most recent call.

Since: base-4.8.1.0

popCallStack :: CallStack -> CallStack #

Pop the most recent call-site off the CallStack.

This function, like pushCallStack, has no effect on a frozen CallStack.

Since: base-4.9.0.0

prettyCallStack :: CallStack -> String #

Pretty print a CallStack.

Since: base-4.9.0.0

pushCallStack :: ([Char], SrcLoc) -> CallStack -> CallStack #

Push a call-site onto the stack.

This function has no effect on a frozen CallStack.

Since: base-4.9.0.0

withFrozenCallStack :: HasCallStack => (HasCallStack => a) -> a #

Perform some computation without adding new entries to the CallStack.

Since: base-4.9.0.0

Source locations

data SrcLoc #

A single location in the source code.

Since: base-4.8.1.0

Constructors

SrcLoc
Fields srcLocPackage :: [Char] srcLocModule :: [Char] srcLocFile :: [Char] srcLocStartLine :: Int srcLocStartCol :: Int srcLocEndLine :: Int srcLocEndCol :: Int

Instances

Eq SrcLoc #	Since: base-4.9.0.0
Instance details Defined in GHC.Stack.Types Methods (==) :: SrcLoc -> SrcLoc -> Bool Source # (/=) :: SrcLoc -> SrcLoc -> Bool Source #
Show SrcLoc #	Since: base-4.9.0.0
Instance details Defined in GHC.Show Methods showsPrec :: Int -> SrcLoc -> ShowS # show :: SrcLoc -> String # showList :: [SrcLoc] -> ShowS #

prettySrcLoc :: SrcLoc -> String #

Pretty print a SrcLoc.

Since: base-4.9.0.0

Internals

data CostCentreStack #

A cost-centre stack from GHC's cost-center profiler.

data CostCentre #

A cost-centre from GHC's cost-center profiler.

getCurrentCCS :: dummy -> IO (Ptr CostCentreStack) #

Returns the current CostCentreStack (value is nullPtr if the current program was not compiled with profiling support). Takes a dummy argument which can be used to avoid the call to getCurrentCCS being floated out by the simplifier, which would result in an uninformative stack (CAF).

getCCSOf :: a -> IO (Ptr CostCentreStack) #

Get the CostCentreStack associated with the given value.

clearCCS :: IO a -> IO a #

Run a computation with an empty cost-center stack. For example, this is used by the interpreter to run an interpreted computation without the call stack showing that it was invoked from GHC.

ccsCC :: Ptr CostCentreStack -> IO (Ptr CostCentre) #

Get the CostCentre at the head of a CostCentreStack.

ccsParent :: Ptr CostCentreStack -> IO (Ptr CostCentreStack) #

Get the tail of a CostCentreStack.

ccLabel :: Ptr CostCentre -> IO CString #

Get the label of a CostCentre.

ccModule :: Ptr CostCentre -> IO CString #

Get the module of a CostCentre.

ccSrcSpan :: Ptr CostCentre -> IO CString #

Get the source span of a CostCentre.

ccsToStrings :: Ptr CostCentreStack -> IO [String] #

Format a CostCentreStack as a list of lines.

renderStack :: [String] -> String #