Copyright  (c) 2016 Allele Dev; 2017 Ixperta Solutions s.r.o.; 2017 Alexis King 

License  BSD3 
Maintainer  Alexis King <lexi.lambda@gmail.com> 
Stability  experimental 
Portability  GHC specific language extensions. 
Safe Haskell  None 
Language  Haskell2010 
Open unions (typeindexed coproducts, i.e. typeindexed sums) for extensible effects All operations are constanttime.
Synopsis
 data Union (r :: [ Type > Type ]) a
 class Weakens q where
 type family xs :++: ys where ...
 decomp :: Union (t ': r) a > Either ( Union r a) (t a)
 weaken :: Union r a > Union (any ': r) a
 extract :: Union '[t] a > t a
 class FindElem eff effs => Member (eff :: Type > Type ) effs where
 type family Members effs effs' :: Constraint where ...
 class Member m effs => LastMember m effs  effs > m
Open Union
data Union (r :: [ Type > Type ]) a Source #
Open union is a strong sum (existential with an evidence).
Open Union Operations
Open Union Membership Constraints
class FindElem eff effs => Member (eff :: Type > Type ) effs where Source #
A constraint that requires that a particular effect,
eff
, is a member of
the typelevel list
effs
. This is used to parameterize an
Eff
computation over an arbitrary list of effects, so
long as
eff
is
somewhere
in the list.
For example, a computation that only needs access to a cell of mutable state
containing an
Integer
would likely use the following type:
Member
(State
Integer
) effs =>Eff
effs ()
type family Members effs effs' :: Constraint where ... Source #
A shorthand constraint that represents a combination of multiple
Member
constraints. That is, the following
Members
constraint:
Members
'[Foo, Bar, Baz] effs
…is equivalent to the following set of
Member
constraints:
(Member
Foo effs,Member
Bar effs,Member
baz effs)
Note that, since each effect is translated into a separate
Member
constraint, the order of the effects does
not
matter.
class Member m effs => LastMember m effs  effs > m Source #
Like
Member
,
is a constraint that requires that
LastMember
eff effs
eff
is in the typelevel list
effs
. However,
unlike
Member
,
LastMember
requires
m
be the
final
effect in
effs
.
Generally, this is not especially useful, since it is preferable for
computations to be agnostic to the order of effects, but it is quite useful
in combination with
sendM
or
liftBase
to embed ordinary monadic effects within an
Eff
computation.
Instances
LastMember m '[m] Source #  
Defined in Data.OpenUnion 

LastMember m effs => LastMember m (eff ': effs) Source #  
Defined in Data.OpenUnion 