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doc: some doc-strings for Option #3868

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Apr 11, 2024
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doc: some doc-strings for Option #3868

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17 changes: 16 additions & 1 deletion src/Init/Data/Option/Basic.lean
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Original file line number Diff line number Diff line change
Expand Up @@ -21,21 +21,26 @@ def toMonad [Monad m] [Alternative m] : Option α → m α
| some _ => true
| none => false

/-- Returns `true` on `some x` and `false` on `none`. -/
@[inline] def isSome : Option α → Bool
| some _ => true
| none => false

/-- Returns `true` on `none` and `false` on `some x`. -/
@[inline] def isNone : Option α → Bool
| some _ => false
| none => true

/--
`x?.isEqSome y` is equivalent to `x? == some y`, but avoids an allocation.
-/
@[inline] def isEqSome [BEq α] : Option α → α → Bool
| some a, b => a == b
| none, _ => false

@[inline] protected def bind : Option α → (α → Option β) → Option β
| none, _ => none
| some a, b => b a
| some a, f => f a

/-- Runs `f` on `o`'s value, if any, and returns its result, or else returns `none`. -/
@[inline] protected def bindM [Monad m] (f : α → m (Option β)) (o : Option α) : m (Option β) := do
Expand All @@ -44,6 +49,10 @@ def toMonad [Monad m] [Alternative m] : Option α → m α
else
return none

/--
Runs a monadic function `f` on an optional value.
If the optional value is `none` the function is not called.
-/
@[inline] protected def mapM [Monad m] (f : α → m β) (o : Option α) : m (Option β) := do
if let some a := o then
return some (← f a)
Expand All @@ -53,18 +62,24 @@ def toMonad [Monad m] [Alternative m] : Option α → m α
theorem map_id : (Option.map id : Option α → Option α) = id :=
funext (fun o => match o with | none => rfl | some _ => rfl)

/-- Keeps an optional value only if it satisfies the predicate `p`. -/
@[always_inline, inline] protected def filter (p : α → Bool) : Option α → Option α
| some a => if p a then some a else none
| none => none

/-- Checks that an optional value satisfies a predicate `p` or is `none`. -/
@[always_inline, inline] protected def all (p : α → Bool) : Option α → Bool
| some a => p a
| none => true

/-- Checks that an optional value is not `none` and the value satisfies a predicate `p`. -/
@[always_inline, inline] protected def any (p : α → Bool) : Option α → Bool
| some a => p a
| none => false

/--
Implementation of `OrElse`'s `<|>` syntax for `Option`.
-/
@[always_inline, macro_inline] protected def orElse : Option α → (Unit → Option α) → Option α
| some a, _ => some a
| none, b => b ()
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