Init.Control.Option

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instance instToBoolOption {α : Type u_1} :

ToBool (Option α)

Equations

instToBoolOption = { toBool := Option.isSome }

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def OptionT (m : Type u → Type v) (α : Type u) :

Type v

Adds the ability to fail to a monad. Unlike ordinary exceptions, there is no way to signal why a failure occurred.

Equations

OptionT m α = m (Option α)

Instances For

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@[inline]

def OptionT.run {m : Type u → Type v} {α : Type u} (x : OptionT m α) :

m (Option α)

Executes an action that might fail in the underlying monad m, returning none in case of failure.

Equations

x.run = x

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def OptionT.mk {m : Type u → Type v} {α : Type u} (x : m (Option α)) :

OptionT m α

Converts an action that returns an Option into one that might fail, with none indicating failure.

Equations

OptionT.mk x = x

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@[inline]

def OptionT.bind {m : Type u → Type v} [Monad m] {α β : Type u} (x : OptionT m α) (f : α → OptionT m β) :

OptionT m β

Sequences two potentially-failing actions. The second action is run only if the first succeeds.

Equations

x.bind f = OptionT.mk do let __do_lift ← x match __do_lift with | some a => f a | none => pure none

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@[inline]

def OptionT.pure {m : Type u → Type v} [Monad m] {α : Type u} (a : α) :

OptionT m α

Succeeds with the provided value.

Equations

OptionT.pure a = OptionT.mk (pure (some a))

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@[always_inline]

instance OptionT.instMonad {m : Type u → Type v} [Monad m] :

Monad (OptionT m)

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One or more equations did not get rendered due to their size.

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instance OptionT.instInhabitedOfPure {α : Type u} {m : Type u → Type v} [Pure m] :

Inhabited (OptionT m α)

Equations

OptionT.instInhabitedOfPure = { default := pure default }

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@[inline]

def OptionT.orElse {m : Type u → Type v} [Monad m] {α : Type u} (x : OptionT m α) (y : Unit → OptionT m α) :

OptionT m α

Recovers from failures. Typically used via the <|> operator.

Equations

x.orElse y = OptionT.mk do let __do_lift ← x match __do_lift with | some a => pure (some a) | x => y ()

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@[inline]

def OptionT.fail {m : Type u → Type v} [Monad m] {α : Type u} :

OptionT m α

A recoverable failure.

Equations

OptionT.fail = OptionT.mk (pure none)

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instance OptionT.instAlternative {m : Type u → Type v} [Monad m] :

Alternative (OptionT m)

Equations

OptionT.instAlternative = { toApplicative := OptionT.instMonad.toApplicative, failure := fun {α : Type ?u.15} => OptionT.fail, orElse := fun {α : Type ?u.15} => OptionT.orElse }

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@[inline]

def OptionT.lift {m : Type u → Type v} [Monad m] {α : Type u} (x : m α) :

OptionT m α

Converts a computation from the underlying monad into one that could fail, even though it does not.

This function is typically implicitly accessed via a MonadLiftT instance as part of automatic lifting.

Equations

OptionT.lift x = OptionT.mk do let __do_lift ← x pure (some __do_lift)

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instance OptionT.instMonadLift {m : Type u → Type v} [Monad m] :

MonadLift m (OptionT m)

Equations

OptionT.instMonadLift = { monadLift := fun {α : Type ?u.14} => OptionT.lift }

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instance OptionT.instMonadFunctor {m : Type u → Type v} :

MonadFunctor m (OptionT m)

Equations

OptionT.instMonadFunctor = { monadMap := fun {α : Type ?u.14} (f : {β : Type ?u.14} → m β → m β) (x : OptionT m α) => f x }

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@[inline]

def OptionT.tryCatch {m : Type u → Type v} [Monad m] {α : Type u} (x : OptionT m α) (handle : Unit → OptionT m α) :

OptionT m α

Handles failures by treating them as exceptions of type Unit.

Equations

x.tryCatch handle = OptionT.mk do let __discr ← x match __discr with | some a => pure (some a) | x => handle ()

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instance OptionT.instMonadExceptOfUnit {m : Type u → Type v} [Monad m] :

MonadExceptOf Unit (OptionT m)

Equations

OptionT.instMonadExceptOfUnit = { throw := fun {α : Type ?u.16} (x : Unit) => OptionT.fail, tryCatch := fun {α : Type ?u.16} => OptionT.tryCatch }

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instance OptionT.instMonadExceptOf {m : Type u → Type v} (ε : Type u) [MonadExceptOf ε m] :

MonadExceptOf ε (OptionT m)

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instance instMonadControlOptionTOfMonad {m : Type u_1 → Type u_2} [Monad m] :

MonadControl m (OptionT m)

Equations

One or more equations did not get rendered due to their size.