| Copyright | (c) The University of Glasgow 1998-2002 |
|---|---|
| License | see libraries/base/LICENSE |
| Maintainer | cvs-ghc@haskell.org |
| Stability | internal |
| Portability | non-portable (GHC extensions) |
| Safe Haskell | Trustworthy |
| Language | Haskell2010 |
GHC.Exception
Description
Exceptions and exception-handling functions.
Synopsis
- module GHC.Exception.Type
- throw :: forall (r :: RuntimeRep). forall (a :: TYPE r). forall e. Exception e => e -> a
- data ErrorCall where
- errorCallException :: String -> SomeException
- errorCallWithCallStackException :: String -> CallStack -> SomeException
- data CallStack
- fromCallSiteList :: [([Char], SrcLoc)] -> CallStack
- getCallStack :: CallStack -> [([Char], SrcLoc)]
- prettyCallStack :: CallStack -> String
- prettyCallStackLines :: CallStack -> [String]
- showCCSStack :: [String] -> [String]
- data SrcLoc = SrcLoc {
- srcLocPackage :: [Char]
- srcLocModule :: [Char]
- srcLocFile :: [Char]
- srcLocStartLine :: Int
- srcLocStartCol :: Int
- srcLocEndLine :: Int
- srcLocEndCol :: Int
- prettySrcLoc :: SrcLoc -> String
Documentation
module GHC.Exception.Type
throw :: forall (r :: RuntimeRep). forall (a :: TYPE r). forall e. Exception e => e -> a #
Throw an exception. Exceptions may be thrown from purely
functional code, but may only be caught within the IO monad.
This is thrown when the user calls error. The first String is the
argument given to error, second String is the location.
Constructors
| ErrorCallWithLocation String String |
Instances
| Exception ErrorCall # | Since: base-4.0.0.0 |
Defined in GHC.Exception Methods toException :: ErrorCall -> SomeException # fromException :: SomeException -> Maybe ErrorCall # displayException :: ErrorCall -> String # | |
| Show ErrorCall # | Since: base-4.0.0.0 |
| Eq ErrorCall # | Since: base-4.7.0.0 |
| Ord ErrorCall # | Since: base-4.7.0.0 |
Defined in GHC.Exception | |
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
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
prettyCallStack :: CallStack -> String #
Pretty print a CallStack.
Since: base-4.9.0.0
prettyCallStackLines :: CallStack -> [String] #
showCCSStack :: [String] -> [String] #
A single location in the source code.
Since: base-4.8.1.0
Constructors
| SrcLoc | |
Fields
| |
Instances
prettySrcLoc :: SrcLoc -> String #
Pretty print a SrcLoc.
Since: base-4.9.0.0