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GHC 9.10.3 · lts/ghc-9.10.x · 248f8f0 · 2026-10-05

Modulepolysemy-1.9.2.0Haskell2010

Polysemy.Internal.Combinators

  • 17 values
  • Packagepolysemy-1.9.2.0
  • Exports17
  • LanguageHaskell2010
  • LicenceBSD-3-Clause
  • SourceCombinators.hs

First order

7 declarations
valueinterpret
  1. :: FirstOrder e "interpret"
  2. => (forall (rInitial :: EffectRow) x. e (Sem rInitial) x -> Sem r x)

    A natural transformation from the handled effect to other effects already in Sem.

  3. -> Sem (e ': r) a
  4. -> Sem r a
#

The simplest way to produce an effect handler. Interprets an effect e by transforming it into other effects inside of r.

valueintercept
  1. :: (Member e r, FirstOrder e "intercept")
  2. => (forall x (rInitial :: EffectRow). e (Sem rInitial) x -> Sem r x)

    A natural transformation from the handled effect to other effects already in Sem.

  3. -> Sem r a

    Unlike interpret, intercept does not consume any effects.

  4. -> Sem r a
#

Like interpret, but instead of handling the effect, allows responding to the effect while leaving it unhandled. This allows you, for example, to intercept other effects and insert logic around them.

valuereinterpret
  1. :: FirstOrder e1 "reinterpret"
  2. => (forall (rInitial :: EffectRow) x. e1 (Sem rInitial) x -> Sem (e2 ': r) x)

    A natural transformation from the handled effect to the new effect.

  3. -> Sem (e1 ': r) a
  4. -> Sem (e2 ': r) a
#

Like interpret, but instead of removing the effect e, reencodes it in some new effect f. This function will fuse when followed by runState, meaning it's free to reinterpret in terms of the State effect and immediately run it.

valuereinterpret2
  1. :: FirstOrder e1 "reinterpret2"
  2. => (forall (rInitial :: EffectRow) x. e1 (Sem rInitial) x -> Sem (e2 ': e3 ': r) x)

    A natural transformation from the handled effect to the new effects.

  3. -> Sem (e1 ': r) a
  4. -> Sem (e2 ': e3 ': r) a
#

Like reinterpret, but introduces two intermediary effects.

valuereinterpret3
  1. :: FirstOrder e1 "reinterpret3"
  2. => (forall (rInitial :: EffectRow) x. e1 (Sem rInitial) x -> Sem (e2 ': e3 ': e4 ': r) x)

    A natural transformation from the handled effect to the new effects.

  3. -> Sem (e1 ': r) a
  4. -> Sem (e2 ': e3 ': e4 ': r) a
#

Like reinterpret, but introduces three intermediary effects.

valuerewrite
  1. :: forall (rInitial :: EffectRow) x. e1 (Sem rInitial) x -> e2 (Sem rInitial) x
  2. -> Sem (e1 ': r) a
  3. -> Sem (e2 ': r) a
#

Rewrite an effect e1 directly into e2, and put it on the top of the effect stack.

valuetransform
  1. :: Member e2 r
  2. => forall (rInitial :: EffectRow) x. e1 (Sem rInitial) x -> e2 (Sem rInitial) x
  3. -> Sem (e1 ': r) a
  4. -> Sem r a
#

Transform an effect e1 into an effect e2 that is already somewhere inside of the stack.

Higher order

6 declarations
valueinterpretH
  1. :: (forall (rInitial :: EffectRow) x. e (Sem rInitial) x -> Tactical e (Sem rInitial) r x)

    A natural transformation from the handled effect to other effects already in Sem.

  2. -> Sem (e ': r) a
  3. -> Sem r a
#

Like interpret, but for higher-order effects (ie. those which make use of the m parameter.)

See the notes on Tactical for how to use this function.

valuereinterpretH
  1. :: (forall (rInitial :: EffectRow) x. e1 (Sem rInitial) x -> Tactical e1 (Sem rInitial) (e2 ': r) x)

    A natural transformation from the handled effect to the new effect.

  2. -> Sem (e1 ': r) a
  3. -> Sem (e2 ': r) a
#

Like reinterpret, but for higher-order effects.

See the notes on Tactical for how to use this function.

valuereinterpret2H
  1. :: (forall (rInitial :: EffectRow) x. e1 (Sem rInitial) x -> Tactical e1 (Sem rInitial) (e2 ': e3 ': r) x)

    A natural transformation from the handled effect to the new effects.

  2. -> Sem (e1 ': r) a
  3. -> Sem (e2 ': e3 ': r) a
#

Like reinterpret2, but for higher-order effects.

See the notes on Tactical for how to use this function.

valuereinterpret3H
  1. :: (forall (rInitial :: EffectRow) x. e1 (Sem rInitial) x -> Tactical e1 (Sem rInitial) (e2 ': e3 ': e4 ': r) x)

    A natural transformation from the handled effect to the new effects.

  2. -> Sem (e1 ': r) a
  3. -> Sem (e2 ': e3 ': e4 ': r) a
#

Like reinterpret3, but for higher-order effects.

See the notes on Tactical for how to use this function.

Conditional

2 declarations
valueinterceptUsing
  1. :: FirstOrder e "interceptUsing"
  2. => ElemOf e r

    A proof that the handled effect exists in r. This can be retrieved through membership or tryMembership.

  3. -> (forall x (rInitial :: EffectRow). e (Sem rInitial) x -> Sem r x)

    A natural transformation from the handled effect to other effects already in Sem.

  4. -> Sem r a

    Unlike interpret, intercept does not consume any effects.

  5. -> Sem r a
#

A variant of intercept that accepts an explicit proof that the effect is in the effect stack rather then requiring a Member constraint.

This is useful in conjunction with tryMembership in order to conditionally perform intercept.

valueinterceptUsingH
  1. :: ElemOf e r

    A proof that the handled effect exists in r. This can be retrieved through membership or tryMembership.

  2. -> (forall x (rInitial :: EffectRow). e (Sem rInitial) x -> Tactical e (Sem rInitial) r x)

    A natural transformation from the handled effect to other effects already in Sem.

  3. -> Sem r a

    Unlike interpretH, interceptUsingH does not consume any effects.

  4. -> Sem r a
#

A variant of interceptH that accepts an explicit proof that the effect is in the effect stack rather then requiring a Member constraint.

This is useful in conjunction with tryMembership in order to conditionally perform interceptH.

See the notes on Tactical for how to use this function.

Statefulness

2 declarations