oeiuwq.com
An Algebraic Effect System for Golang.
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fx.go
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fx.go
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package fx
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type Fx[S, V any] struct {
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// an immediate value
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imm func() V
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// the continuation of a suspended effect
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sus func(S) Fx[S, V]
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stp func() Fx[S, V]
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// the resume function of an stopped effect
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res func() Fx[S, V]
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}
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type FxPure[V any] = Fx[Nil, V]
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func Ctx[V any]() Fx[V, V] { return Func(identity[V]) }
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// An stopped effect that panics if restarted
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// An stopped effect that panics if resumed
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func Halt[S, V any]() Fx[S, V] {
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return Stop(func() Fx[S, V] {
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panic("tried to restart halted effect. try using fx.Replace instead")
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return Fx[S, V]{
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imm: func() V {
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panic("tried to Resume a halted effect. try using Replace instead")
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},
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}
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})
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}
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func Stop[S, V any](f func() Fx[S, V]) Fx[S, V] { return Fx[S, V]{stp: f} }
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// Creates an stopped effect from a resume function
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func Stop[S, V any](e func() Fx[S, V]) Fx[S, V] {
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return Fx[S, V]{res: e}
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}
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// Replace with y if x is already stopped. Otherwise x continues.
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// Resume an effect if it was previously stopped.
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func Resume[S, V any](e Fx[S, V]) Fx[S, V] {
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if e.res != nil {
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return e.res()
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}
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return e
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}
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// Replace with y if x is already Halted. Otherwise x continues.
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func Replace[S, V any](y func() Fx[S, V]) func(Fx[S, V]) Fx[S, V] {
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return func(x Fx[S, V]) Fx[S, V] {
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if x.stp != nil {
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if x.res != nil {
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return y()
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}
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if x.imm != nil {
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// Continue an effect by transforming its immediate value into another effect.
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func Then[T, U, S, V any](cmap func(T) S, fmap func(V) Fx[T, U]) func(Fx[S, V]) Fx[T, U] {
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return func(e Fx[S, V]) Fx[T, U] {
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if e.stp != nil {
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return Stop(func() Fx[T, U] {
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return Then(cmap, fmap)(e.stp())
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})
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if e.res != nil {
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return Stop(func() Fx[T, U] { return Then(cmap, fmap)(e.res()) })
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}
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if e.imm != nil {
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return fmap(e.imm())
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func ContraMap[V, S, R any](f func(R) S) func(Fx[S, V]) Fx[R, V] {
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return func(e Fx[S, V]) Fx[R, V] {
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if e.stp != nil {
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return Stop(func() Fx[R, V] {
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return ContraMap[V](f)(e.stp())
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})
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if e.res != nil {
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return Stop(func() Fx[R, V] { return ContraMap[V](f)(e.res()) })
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}
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if e.imm != nil {
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return Const[R](e.imm())
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}
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func ProvideLeft[A, B, V any](e Fx[And[A, B], V], a A) Fx[B, V] {
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if e.stp != nil {
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return Stop(func() Fx[B, V] {
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return ProvideLeft(e.stp(), a)
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})
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if e.res != nil {
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return Stop(func() Fx[B, V] { return ProvideLeft(e.res(), a) })
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}
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if e.imm != nil {
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return Const[B](e.imm())
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loop = func(e Fx[And[A, B], V]) Fx[B, V] {
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for {
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e = e.sus(ab)
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if e.stp != nil {
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return Stop(func() Fx[B, V] {
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return loop(e.stp())
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})
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if e.res != nil {
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return Stop(func() Fx[B, V] { return loop(e.res()) })
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}
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if e.imm != nil {
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return Const[B](e.imm())
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func Eval[V any](e Fx[Nil, V]) V {
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for {
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if e.stp != nil {
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if e.res != nil {
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panic("tried to evaluate halted effect. try using fx.Replace with another effect.")
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}
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if e.imm != nil {