Safe Haskell | Safe-Inferred |
---|---|
Language | Haskell2010 |
Synopsis
- type WithCallStack a = HasCallStack => a
- data CallStack
- annotateCallStackIO :: WithCallStack (IO a -> IO a)
- withFrozenCallStack :: HasCallStack => (HasCallStack => a) -> a
- withLexicalCallStack :: (a -> WithCallStack (IO b)) -> WithCallStack (a -> IO b)
- callStack :: HasCallStack => CallStack
- prettyCallStack :: CallStack -> String
- parentSrcLocPrefix :: WithCallStack String
Documentation
type WithCallStack a = HasCallStack => a Source #
CallStack
s 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 aHasCallStack
constraint -- GHC will append the new call-site to the existingCallStack
. - 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 aHasCallStack
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 theHasCallStack
constraint for the singletonCallStack
containing just the current call-site.
CallStack
s 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
annotateCallStackIO :: WithCallStack (IO a -> IO a) Source #
This function is for when you *really* want to add a call
stack to raised IO, but you don't have a
Verbosity
so you can't use
annotateIO
. If you have a Verbosity
,
please use that function instead.
withFrozenCallStack :: HasCallStack => (HasCallStack => a) -> a Source #
Perform some computation without adding new entries to the CallStack
.
Since: base-4.9.0.0
withLexicalCallStack :: (a -> WithCallStack (IO b)) -> WithCallStack (a -> IO b) Source #
callStack :: HasCallStack => CallStack Source #
parentSrcLocPrefix :: WithCallStack String Source #
Give the *parent* of the person who invoked this;
so it's most suitable for being called from a utility function.
You probably want to call this using withFrozenCallStack
; otherwise
it's not very useful. We didn't implement this for base-4.8.1
because we cannot rely on freezing to have taken place.