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fused-effects v1.0.0.0 Release Notes

Release Date: 2019-11-11 // over 4 years ago

    • ➕ Adds an Empty effect, modelling nondeterminism without choice (#196).

    • ➕ Adds an EmptyC carrier for Empty. (#196)

    • ➕ Adds a Choose effect, modelling nondeterminism without failure (#198).

    • ➕ Adds a Throw effect, modelling failure with a value. (#247)

    • ➕ Adds a Catch effect which can be used with Throw (or other kinds of failure) to model recoverable failure. (#247)

    • ➕ Adds a oneOf function to Control.Effect.NonDet to provide an idiom for the common case of nondeterministically selecting from a container. (#201)

    • ➕ Adds a foldMapA function to Control.Effect.NonDet mapping containers into nondeterministic computations using a supplied function. (#204)

    • Defines a new Has constraint synonym, conveniently combining Carrier and Member constraints and used for all effect constructors. (#217)

    • 👍 Allows effects to be defined and handled as sums of other effects, while still using the constructors for the component effects. This has been used to redefine NonDet as a sum of Empty and Choose, and Error as a sum of Throw and Catch. (#199, #219, #247)

    • Defines Carrier instances for a number of types in base, including Either, Maybe, [], and IO. (#206)

    • Defines Carrier instances for a number of types in transformers. (#226)

    • Defines an evalFresh handler for Control.Carrier.Strict.FreshC, taking the initial value. (#267)

    Backwards-incompatible changes

    • 💅 Renames the Carrier class to Algebra and its eff method to alg, and moved the responsibilities of Control.Carrier to Control.Algebra. This makes the library more consistent with the literature and encourages a style of naming that focuses on morphisms rather than objects. (#285, #294)

    • 🛠 Fixes unlawful behaviour in the Applicative instance for ErrorC, which had different behaviour between <*> and ap in the presence of a divergent rhs. In order to accomplish this, ErrorC has been defined as a wrapper around Control.Monad.Trans.Except.ExceptT. (#228)

    • 👌 Improves the performance of runInterpret using reflection, changing its signature slightly (#193, h/t @ocharles).

    • ✂ Removes Control.Effect.Random (and the dependencies on random & MonadRandom) in favour of a new fused-effects-random package (#200).

    • ✂ Removes fmap' and handlePure, both deprecated in 0.5.0.0 (#205).

    • Redefines NonDetC as a Church-encoded binary tree instead of a Church-encoded list (#197).

    • ✂ Removes the OnceC carrier for Cull effects, replacing it with the composition of CullC on some other Alternative carrier, e.g. NonDetC (#204).

    • 🚚 Moves all the carriers into their own modules in the Control.Carrier namespace. Several have also been renamed, e.g. the various Trace carriers are all named TraceC within their separate modules, and should be imported qualified if disambiguation is required. This simplifies naming schemes, and ensures that the choice of e.g. strict or lazy carrier is always made consciously and expliclty, instead of defaulting to whichever is exported by the effect module (#204).

    • ✂ Removes the re-export of Member from all carrier modules, re-exporting Has in its place. Has constraints should generally be used instead, and specialist cases can import Control.Effect.Sum for Member. (#217)

    • Redesigns & renames the handlers for church-encoded nondeterminism carriers to standardize naming and usage patterns. (#207)

      • The primary handlers (runChoose, runNonDet, runCut, runCull) take multiple continuations.
      • Handlers which return an Alternative are suffixed with A, e.g. runNonDetA.
      • Handlers which return a Monoid are suffixed with M, e.g. runNonDetM.
      • Handlers which return a Semigroup are suffixed with S, e.g. runChooseS.

    • ✂ Removes InterposeC & runInterpose due to their inefficiency. They can be replaced with use of InterpretC/runInterpret for the desired effect. (#223)

    • ✂ Removes prj from Member, as it was only used in InterposeC (see above), and was generally inadvisable due to its lack of modularity. (#223)

    • ✂ Removes the Resource effect and carrier. Both have been relocated to fused-effects-exceptions. (#268)

    • Redefines Fail as a synonym for Throw String. (#247)

    • ✂ Removes Resumable and its carriers. Both have been relocated to fused-effects-resumable; they can also be usefully and flexibly replaced by arbitrary effects, Lift, and InterpretC. (#269)

    • 🔄 Changes Control.Carrier.Fresh.Strict.runFresh to take and return the initial & final values, respectively, allowing for safer operation. (#267)

    • Removes resetFresh, as it was unsafe. Greater safety and control over the generation of fresh values can be obtained by use of runFresh. (#267)

    • ✂ Removes PureC; Data.Functor.Identity.Identity should be used instead. Note that run is still provided as a convenient synonym for runIdentity. (#307)

    • ✂ Removes the Pure effect. It’s unlikely that this will require changes, as Pure had no operations, but Lift Identity should be used instead. (#307)

    • 👻 Redefines the Lift effect, allowing inner contexts to run actions in outer contexts, e.g. to interoperate with Control.Exception. (#306)

    • ✂ Removes MonadUnliftIO instances as they’ve been subsumed by the new definition of Lift. Additionally, the ReaderT & IdentityT types defined in transformers may be useful. (#306)