Providing Requirements

Effect requirements can be provided in any order with no impact in the evaluation of the program.

Provide* Combinators.

These functions are used to eliminate requirements from effects. Only when Nil is the only remaining requirement, the effect can be evaluated.

The result of provide functions will always be another effect, meaning that no computation has been performed yet, nor any side-effect produced. The result is just another effect but with less requirements.

// Discharges the single S requirement.
func Provide(Fx[S, V], S) Fx[Nil, V]


// Discharges the requirement of A by providing it.
func ProvideLeft(Fx[And[A, B], V], A) Fx[B, V]

// Discharges the requirement of B by providing it.
func ProvideRight(Fx[And[A, B], V], B) Fx[A, V]

// Discharges both A and B
func ProvideBoth(Fx[And[A, B], V], A, B) Fx[Nil, V]



// Provides A, the first part of the left And.
func ProvideFirstLeft(Fx[And[And[A, C], And[B, D]], V], A) Fx[And[C, And[B, D]], V]

// Provides B, the first part of the right And.
func ProvideFirstRight(Fx[And[And[A, C], And[B, D]], V], B) Fx[And[And[A, C], D], V]

// Provides A and B, the first part of both Ands.
func ProvideFirsts(Fx[And[And[A, C], And[B, D]], V], A, B) Fx[And[C, D], V]