class Lean.MonadBacktrack (s : outParam Type) (m : Type → Type) : Type

Similar to MonadState, but it retrieves/restores only the "backtrackable" part of the state

• saveState : m s
• restoreState : s → m Unit

def Lean.commitWhenSome? {m : Type → Type} {s : Type} {ε : Type u_1} {α : Type} [Monad m] [MonadBacktrack s m] [MonadExcept ε m] (x? : m (Option α)) : m (Option α)

Execute x?, but backtrack state if result is none or an exception was thrown.

Equations

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def Lean.commitWhenSomeNoEx? {m : Type → Type} {s : Type} {ε : Type u_1} {α : Type} [Monad m] [MonadBacktrack s m] [MonadExcept ε m] (x? : m (Option α)) : m (Option α)

Execute x?, but backtrack state if result is none or an exception was thrown. If an exception is thrown, none is returned. That is, this function is similar to commitWhenSome?, but swallows the exception and returns none.

Equations

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def Lean.commitWhen {m : Type → Type} {s : Type} {ε : Type u_1} [Monad m] [MonadBacktrack s m] [MonadExcept ε m] (x : m Bool) : m Bool

Equations

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def Lean.commitIfNoEx {m : Type → Type} {s : Type} {ε : Type u_1} {α : Type} [Monad m] [MonadBacktrack s m] [MonadExcept ε m] (x : m α) : m α

Equations

• Lean.commitIfNoEx x = do let s_1 ← Lean.saveState tryCatch x fun (ex : ε) => do Lean.restoreState s_1 throw ex

def Lean.withoutModifyingState {m : Type → Type} {s α : Type} [Monad m] [MonadFinally m] [MonadBacktrack s m] (x : m α) : m α

Equations

• Lean.withoutModifyingState x = do let s_1 ← Lean.saveState tryFinally x (Lean.restoreState s_1)

def Lean.observing? {m : Type → Type} {s : Type} {ε : Type u_1} {α : Type} [Monad m] [MonadBacktrack s m] [MonadExcept ε m] (x : m α) : m (Option α)

Equations

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instance Lean.instMonadBacktrackExceptTOfMonad {s : Type} {m : Type → Type} {ε : Type} [MonadBacktrack s m] [Monad m] : MonadBacktrack s (ExceptT ε m)

Equations

• Lean.instMonadBacktrackExceptTOfMonad = { saveState := ExceptT.lift Lean.saveState, restoreState := fun (s_1 : s) => ExceptT.lift (Lean.restoreState s_1) }