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GHC 10.0.0.20260917 · lts/ghc-10.0.x · 8fef28d · 2026-11-02

Modulefused-effects-1.1.2.7Haskell2010

Control.Effect.Throw

An effect for polymorphic failure.

Predefined carriers:

Contents
  1. Throw effect
  2. Re-exports
Synopsis

Throw effect

newtypenewtype Throw e (m :: Type -> Type) k where

Constructors

Instances6Algebra
valuethrowError :: Has (Throw e) sig m => e -> m a

Throw an error, escaping the current computation up to the nearest catchError (if any).

runThrow (throwError e >>= k) = runThrow (throwError e)

Re-exports

classclass Monad m => Algebra (sig :: (Type -> Type) -> Type -> Type) (m :: Type -> Type) | m -> sig where

The class of carriers (results) for algebras (effect handlers) over signatures (effects), whose actions are given by the alg method.

Instances53Algebra, …
typetype Has (eff :: (Type -> Type) -> Type -> Type) (sig :: (Type -> Type) -> Type -> Type) (m :: Type -> Type) = (Members eff sig, Algebra sig m)

m is a carrier for sig containing eff.

Note that if eff is a sum, it will be decomposed into multiple Member constraints. While this technically allows one to combine multiple unrelated effects into a single Has constraint, doing so has two significant drawbacks:

  1. Due to a problem with recursive type families, this can lead to significantly slower compiles.

  2. It defeats ghc’s warnings for redundant constraints, and thus can lead to a proliferation of redundant constraints as code is changed.

valuerun :: Identity a -> a

Run an action exhausted of effects to produce its final result value.