fail is:exact

fail :: MonadFail m => String -> m a

base Prelude Control.Monad Control.Monad.Fail, hedgehog Hedgehog.Internal.Prelude, ghc GHC.Prelude.Basic, base-compat Control.Monad.Compat Control.Monad.Compat Prelude.Compat, fail Control.Monad.Fail, relude Relude.Monad.Reexport, rio RIO.Prelude, base-prelude BasePrelude, numeric-prelude NumericPrelude NumericPrelude.Base, universum Universum.Monad.Reexport, base-compat-batteries Control.Monad.Compat, fused-effects Control.Effect.Fail, Cabal-syntax Distribution.Compat.MonadFail Distribution.Compat.Prelude, github GitHub.Internal.Prelude, numhask NumHask.Prelude, ghc-lib-parser GHC.Prelude.Basic, dimensional Numeric.Units.Dimensional.Prelude, rebase Rebase.Prelude, hledger Hledger.Cli.Script, mixed-types-num Numeric.MixedTypes.PreludeHiding, xmonad-contrib XMonad.Config.Prime, stack Stack.Prelude, linear-base Control.Functor.Linear, massiv-test Test.Massiv.Utils, incipit-base Incipit.Base, LambdaHack Game.LambdaHack.Core.Prelude Game.LambdaHack.Core.Prelude, cabal-install-solver Distribution.Solver.Compat.Prelude, can-i-haz Control.Monad.Except.CoHas Control.Monad.Reader.Has, yesod-paginator Yesod.Paginator.Prelude, faktory Faktory.Prelude, hledger-web Hledger.Web.Import, zio ZIO.Trans

fail :: Plus m => String -> m a

semigroupoids Semigroupoids.Do

Important note

This ignores whatever String you give it. It is a bad idea to use fail as a form of labelled error; instead, it should only be defaulted to when a pattern match fails.

package fail

Uses

Forward-compatible MonadFail class This package contains the Control.Monad.Fail module providing the MonadFail class that became available in base-4.9.0.0 for older base package versions. This package turns into an empty package when used with GHC versions which already provide the Control.Monad.Fail module to make way for GHC's own Control.Monad.Fail module.

fail :: Monad m => String -> m a

basic-prelude CorePrelude, prelude-compat Prelude2010

Fail with a message. This operation is not part of the mathematical definition of a monad, but is invoked on pattern-match failure in a do expression. As part of the MonadFail proposal (MFP), this function is moved to its own class MonadFail (see Control.Monad.Fail for more details). The definition here will be removed in a future release.

fail :: e -> Parser e s a

bytesmith Data.Bytes.Parser

Fail with the provided error message.

fail :: Text -> Parse output

ptr Ptr.Parse

fail :: Text -> ParseUnbound output

ptr Ptr.ParseUnbound

fail :: PolyCont Return IOError r Void => String -> r

control-dsl Control.Dsl Control.Dsl.Return

Lift an IOError to the answer type, similar to fail. This fail function aims to be used as the last statement of a do block.

fail :: Monad m => e -> Valor i m e

valor Data.Valor

Constructs a validator that always fails with provided error e.

Example

>>> validateP ( fail "YOU SHALL NOT PASS!!!" ) 1
Right "YOU SHALL NOT PASS!!!"