eff
This cache is used to memoize values for the Memoized effect
Collection of effects of a given type from a Unions objects
Sequence of monadic functions from A to B: A => Eff[B]
Sequence of monadic functions from A to B: A => Eff[B]
Internally it is represented as a Vector of functions:
A => Eff[R, X1]; X1 => Eff[R, X2]; X2 => Eff[R, X3]; ...; X3 => Eff[R, B]
An alternate unit value can also be set on this function in case the argument A is not available. This value can be set by an effect to do some cleanup if it doesn't even get the chance to add its own effect. See SafeEffect.bracket
Effects of type R, returning a value of type A
Effects of type R, returning a value of type A
It is implemented as a "Free-er" monad with extensible effects:
Arrs typeThe monad implementation for this type is really simple:
point is Purebind simply appends the binding function to the Arrs continuationImportant:
The list of continuations is NOT implemented as a type sequence but simply as a Vector[Any => Eff[R, Any]]
This means that various .asInstanceOf are present in the implementation and could lead
to burns and severe harm. Use with caution!
Similarly the list of effects in the applicative case is untyped and interpreters for those effects are supposed to create a list of values to feed the mapping function. If an interpreter doesn't create a list of values of the right size and with the right types, there will be a runtime exception.
The Pure, Impure and ImpureAp cases also incorporate a "last" action returning no value but just used for side-effects (shutting down an execution context for example). This action is meant to be executed at the end of all computations, regardless of the number of flatMaps added on the Eff value.
Since this last action will be executed, its value never collected so if it throws an exception it is possible to print it by defining the eff.debuglast system property (-Deff.debuglast=true)
http://okmij.org/ftp/Haskell/extensible/more.pdf
Union represents one effect T[_] embedded in a tree of possible effects R
Union represents one effect T[_] embedded in a tree of possible effects R
The effect tree is represented by four possible cases:
The union type has three concrete constructors:
Effect for computation which can fail and return a Throwable, or just stop with a failure
Effect for computation which can fail and return a Throwable, or just stop with a failure
This effect is a mix of Eval and Either in the sense that every computation passed to this effect (with the ok method) is considered "impure" or "faulty" by default.
The type F is used to represent the failure type.
Base type for a tree of effect types
Append a tree of effects to another one
Impure is an effect (encoded as one possibility among other effects, a Union) and a continuation providing the next Eff value.
Impure is an effect (encoded as one possibility among other effects, a Union) and a continuation providing the next Eff value.
This essentially models a flatMap operation with the current effect and the monadic function to apply to a value once the effect is interpreted
One effect can always be executed last, just for side-effects
ImpureAp is a list of independent effects and a pure function creating a value with all the resulting values once all effects have been interpreted.
ImpureAp is a list of independent effects and a pure function creating a value with all the resulting values once all effects have been interpreted.
This essentially models a sequence + map operation but it is important to understand that the list of Union objects can represent different effects and be like: Vector[Option[Int], Future[String], Option[Int]].
Interpreting such an Eff value for a given effect (say Option) consists in:
VERY IMPORTANT:
The Interpret trait provides method to interpret (or "handle") effects.
The Interpret trait provides method to interpret (or "handle") effects.
An interpreter generally handles a given effect M and a value Eff[R, A] where M is a member of R.
The most general way of interpreting an effect is to implement the Interpreter trait for that effect and
use the runInterpreter method. With the Interpreter trait you need to define:
For each of those methods you get access to a continuation which you may or may not invoke to create the next effect in a sequence of effects. For example with the EitherEffect once you arrive on a Left value you don't trigger the continuation because there is no value to trigger it with.
There are also easier ways to define interpreters. The recurse method and the Recurser trait define:
Even simpler, the Translate trait does a translation from an effect M[X] to other effects in the stack.
There are also a few intercept methods to use an effect but still leave it in the stack
Interpret eff values
Interpret eff values
For stack-safety reasons, the continuation must *never* be called with a value directly, but always with Eff.impure:
Eff.impure(a, continuation)
* *Note* it is the responsibility of the implementation to call continuation.onNone if the continuation is not used to create the return value.
Typeclass proving that it is possible to send a tree of effects R into another tree of effects U
Typeclass proving that it is possible to send a tree of effects R into another tree of effects U
for example
send[Option1, Fx.fx3[Option1, Option2, Option3], Int](Option1(1)). into[Fx.fx5[Option1, Option2, Option3, Option4, Option5]]
should work because all the effects of the first stack are present in the second
Note: some implicit definitions are probably missing in some cases
Encapsulation of one optional last action to execute at the end of the program
The "empty" tree of effects
Helper trait for computations which might produce several M[X] in a stack of effects.
Helper trait for computations which might produce several M[X] in a stack of effects.
Either we can produce an X to pass to a continuation or we're done
For the applicative case we expect to be able to traverse a list of effects and return an effect of a list of results OR completely consume the effect and return a pure list of values
support trait for folding values while possibly keeping some internal state
The Safe type is a mix of a ThrowableEither / Eval effect and a writer effect to collect finalizer failures
type class for effects which can be cached in a SequenceCache
trait for translating one effect into other ones in the same stack
transform a Union for a given stack into a Union for another stack
A non-empty list of Unions.
A non-empty list of Unions.
It is only partially typed, we just keep track of the type of the first object
Effect for logging values alongside computations
Effect for logging values alongside computations
Compared to traditional Writer monad which accumulates values by default this effect can be interpreted in different ways:
Simple instantiation of the ErrorEffect trait with String as a Failure type