def StateT (σ : Type u) (m : Type u → Type v) (α : Type u) : Type (max u v)

Adds a mutable state of type σ to a monad.

Actions in the resulting monad are functions that take an initial state and return, in m, a tuple of a value and a state.

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def StateT.mk {σ : Type u} {m : Type u → Type v} {α : Type u} (x : σ → m (α × σ)) : StateT σ m α

Interpret σ → m (α × σ) as an element of StateT σ m α.

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def StateT.run {σ : Type u} {m : Type u → Type v} {α : Type u} (x : StateT σ m α) (s : σ) : m (α × σ)

Executes an action from a monad with added state in the underlying monad m. Given an initial state, it returns a value paired with the final state.

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def StateT.run' {σ : Type u} {m : Type u → Type v} [Functor m] {α : Type u} (x : StateT σ m α) (s : σ) : m α

Executes an action from a monad with added state in the underlying monad m. Given an initial state, it returns a value, discarding the final state.

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def StateM (σ α : Type u) : Type u

A tuple-based state monad.

Actions in StateM σ are functions that take an initial state and return a value paired with a final state.

instance instSubsingletonStateM {σ α : Type u_1} [Subsingleton σ] [Subsingleton α] : Subsingleton (StateM σ α)

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

Returns the given value without modifying the state. Typically used via Pure.pure.

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

Sequences two actions. Typically used via the >>= operator.

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def StateT.map {σ : Type u} {m : Type u → Type v} [Monad m] {α β : Type u} (f : α → β) (x : StateT σ m α) : StateT σ m β

Modifies the value returned by a computation. Typically used via the <$> operator.

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instance StateT.instMonad {σ : Type u} {m : Type u → Type v} [Monad m] : Monad (StateT σ m)

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def StateT.orElse {σ : Type u} {m : Type u → Type v} [Alternative m] {α : Type u} (x₁ : StateT σ m α) (x₂ : Unit → StateT σ m α) : StateT σ m α

Recovers from errors. The state is rolled back on error recovery. Typically used via the <|> operator.

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def StateT.failure {σ : Type u} {m : Type u → Type v} [Alternative m] {α : Type u} : StateT σ m α

Fails with a recoverable error. The state is rolled back on error recovery.

instance StateT.instAlternative {σ : Type u} {m : Type u → Type v} [Monad m] [Alternative m] : Alternative (StateT σ m)

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def StateT.get {σ : Type u} {m : Type u → Type v} [Monad m] : StateT σ m σ

Retrieves the current value of the monad's mutable state.

This increments the reference count of the state, which may inhibit in-place updates.

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def StateT.set {σ : Type u} {m : Type u → Type v} [Monad m] : σ → StateT σ m PUnit

Replaces the mutable state with a new value.

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def StateT.modifyGet {σ : Type u} {m : Type u → Type v} [Monad m] {α : Type u} (f : σ → α × σ) : StateT σ m α

Applies a function to the current state that both computes a new state and a value. The new state replaces the current state, and the value is returned.

It is equivalent to do let (a, s) := f (← StateT.get); StateT.set s; pure a. However, using StateT.modifyGet may lead to better performance because it doesn't add a new reference to the state value, and additional references can inhibit in-place updates of data.

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def StateT.lift {σ : Type u} {m : Type u → Type v} [Monad m] {α : Type u} (t : m α) : StateT σ m α

Runs an action from the underlying monad in the monad with state. The state is not modified.

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

instance StateT.instMonadLift {σ : Type u} {m : Type u → Type v} [Monad m] : MonadLift m (StateT σ m)

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instance StateT.instMonadFunctor (σ : Type u_1) (m : Type u_1 → Type u_2) : MonadFunctor m (StateT σ m)

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instance StateT.instMonadExceptOf {σ : Type u} {m : Type u → Type v} [Monad m] (ε : Type u_1) [MonadExceptOf ε m] : MonadExceptOf ε (StateT σ m)

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def ForM.forIn {m : Type u_1 → Type u_2} {β : Type u_1} {ρ : Type u_3} {α : Type u_4} [Monad m] [ForM (StateT β (ExceptT β m)) ρ α] (x : ρ) (b : β) (f : α → β → m (ForInStep β)) : m β

Creates a suitable implementation of ForIn.forIn from a ForM instance.

instance instMonadStateOfStateTOfMonad {σ : Type u} {m : Type u → Type v} [Monad m] : MonadStateOf σ (StateT σ m)

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instance StateT.monadControl (σ : Type u) (m : Type u → Type v) [Monad m] : MonadControl m (StateT σ m)

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instance StateT.tryFinally {m : Type u → Type v} {σ : Type u} [MonadFinally m] [Monad m] : MonadFinally (StateT σ m)

instance instMonadAttachStateTOfMonad {m : Type u_1 → Type u_2} {σ : Type u_1} [Monad m] [MonadAttach m] : MonadAttach (StateT σ m)