Safe Haskell | None |
---|---|
Language | Haskell2010 |
This module contains Template Haskell functions for generating definitions of functions that send effect operations. You mostly won't want to import this module directly; The Cleff module reexports the main functionalities of this module.
This is an internal module and its API may change even between minor versions. Therefore you should be extra careful if you're to depend on this module.
Documentation
makeEffect :: Name -> Q [Dec] Source #
For a datatype T
representing an effect,
generates functions defintions for performing the
operations of makeEffect
TT
via send
. The naming rule is changing the first uppercase letter in the constructor name to
lowercase or removing the :
symbol in the case of operator constructors. Also, this function will preserve any
fixity declarations defined on the constructors.
Because of the limitations of Template Haskell, all constructors of T
should be polymorphic in the monad type,
if they are to be used by makeEffect
. For example, this is not OK:
data Limited ::Effect
where Noop :: Limited (Eff
es) ()
because the monad type
is not a fully polymorphic type variable.Eff
es
This function is also "weaker" than polysemy
's makeSem
, because this function cannot properly handle some
cases involving complex higher order effects. Those cases are rare, though. See the tests for more details.
makeEffect_ :: Name -> Q [Dec] Source #
Like makeEffect
, but doesn't generate type signatures. This is useful when you want to attach Haddock
documentation to the function signature, e.g.:
data Identity ::Effect
where Noop :: Identity m ()makeEffect_
''Identity -- | Perform nothing at all. noop :: Identity:>
es =>Eff
es ()
Be careful that the function signatures must be added after the makeEffect_
call.
makeSmartCons :: Bool -> Name -> Q [Dec] Source #
This is the function underlying makeEffect
and makeEffect_
. You can switch between the behavior of two by
changing the Bool
parameter to True
(generating signatures) or False
(not generating signatures).