:: a typeCtrl KGHC 10.0.0.20260917 · lts/ghc-10.0.x · fc4e598 · 2026-10-11
Moduleeffectful-core-2.7.1.2GHC2021
Provide the ability to handle errors of type e.
ThrowErrorWith :: (e -> String) -> e -> Error e a bRethrowErrorWith :: (e -> String) -> CallStack -> e -> Error e a bCatchError :: m a -> (CallStack -> e -> m a) -> Error e a btype DispatchOf (Error e) = 'DynamicDefined in effectful-core-2.7.1.2 · Effectful.Internal.Effect.DynamicHandle errors of type e (via Effectful.Error.Static).
runErrorWith Handle errors of type e (via Effectful.Error.Static) with a specific
error handler.
Handle errors of type e (via Effectful.Error.Static). In case of an
error discard the CallStack.
Handle errors of type e (via Effectful.Error.Static) with a specific
error handler. In case of an error discard the CallStack.
throwErrorWith Throw an error of type e and specify a display function in case a
third-party code catches the internal exception and shows it.
Throw an error of type e with show as a display function.
Throw an error of type e with no display function.
rethrowErrorWith rethrowError rethrowError_ Throw an error of type e with the given CallStack and no display
function.
catchError Handle an error of type e.
handleError The same as flip catchError, which is useful in situations where the
code for the handler is shorter.
tryError Similar to catchError, but returns an Either result which is a Right if no error was thrown and a Left otherwise.
Assign a label to an effect.
Note: labeled effects are best used together with the effectful-plugin package, as it significantly improves their usability.
The constructor is for sending labeled operations of a dynamically dispatched effect to the handler:
import Effectful.Dispatch.Dynamic:{ data X :: Effect where X :: X m Int type instance DispatchOf X = Dynamic:}
:{ runPureEff . runLabeled @"x" (interpret_ $ \X -> pure 333) $ do send $ Labeled @"x" X:}333
type DispatchOf (Labeled label e) = DispatchOf eDefined in effectful-core-2.7.1.2 · Effectful.Labeleddata StaticRep (Labeled label e)Defined in effectful-core-2.7.1.2 · Effectful.LabeledRequest 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.
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"helloCallStack (from HasCallStack): putStrLnWithCallStack, called at <interactive>:... in interactive:Ghci...
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.
Extract a list of call-sites from the CallStack.
The list is ordered by most recent call.
Pretty print a CallStack.