| Copyright | (c) The University of Glasgow 2015 |
|---|---|
| License | see libraries/ghc-prim/LICENSE |
| Maintainer | cvs-ghc@haskell.org |
| Stability | internal |
| Portability | non-portable (GHC Extensions) |
| Safe Haskell | Trustworthy |
| Language | Haskell2010 |
GHC.Stack.Types
Description
type definitions for implicit call-stacks. Use GHC.Stack from the base package instead of importing this module directly.
Synopsis
- data CallStack
- type HasCallStack = ?callStack :: CallStack
- emptyCallStack :: CallStack
- freezeCallStack :: CallStack -> CallStack
- fromCallSiteList :: [([Char], SrcLoc)] -> CallStack
- getCallStack :: CallStack -> [([Char], SrcLoc)]
- pushCallStack :: ([Char], SrcLoc) -> CallStack -> CallStack
- data SrcLoc = SrcLoc {
- srcLocPackage :: [Char]
- srcLocModule :: [Char]
- srcLocFile :: [Char]
- srcLocStartLine :: Int
- srcLocStartCol :: Int
- srcLocEndLine :: Int
- srcLocEndCol :: Int
Implicit call stacks
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>:... in interactive:Ghci...
GHC solves HasCallStack constraints in three steps:
- If there is a
CallStackin scope -- i.e. the enclosing function has aHasCallStackconstraint -- GHC will append the new call-site to the existingCallStack. - If there is no
CallStackin scope -- e.g. in the GHCi session above -- and the enclosing definition does not have an explicit type signature, GHC will infer aHasCallStackconstraint for the enclosing definition (subject to the monomorphism restriction). - If there is no
CallStackin scope and the enclosing definition has an explicit type signature, GHC will solve theHasCallStackconstraint for the singletonCallStackcontaining 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
Constructors
| EmptyCallStack | |
| PushCallStack [Char] SrcLoc CallStack | |
| FreezeCallStack CallStack | Freeze the stack at the given |
type HasCallStack = ?callStack :: CallStack Source #
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
emptyCallStack :: CallStack Source #
The empty CallStack.
Since: base-4.9.0.0
freezeCallStack :: CallStack -> CallStack Source #
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 Source #
Convert a list of call-sites to a CallStack.
Since: base-4.9.0.0
getCallStack :: CallStack -> [([Char], SrcLoc)] Source #
Extract a list of call-sites from the CallStack.
The list is ordered by most recent call.
Since: base-4.8.1.0
pushCallStack :: ([Char], SrcLoc) -> CallStack -> CallStack Source #
Push a call-site onto the stack.
This function has no effect on a frozen CallStack.
Since: base-4.9.0.0
Source locations
A single location in the source code.
Since: base-4.8.1.0
Constructors
| SrcLoc | |
Fields
| |