has_some x is true if x is of the form Some y and false otherwise.

Negation of has_some

equal f x y lifts the equality predicate f to option types. That is, if both x and y are None then it returns true, if they are both Some _ then f is called. Otherwise it returns false.

Same as equal, but with comparison.

Lift a hash to option types.

get x returns y where x is Some y.

• raises IsNone

  if x equals None.

make x returns Some x.

bind x f is f y if x is Some y and None otherwise

filter f x is x if x Some y and f y is true, None otherwise

init b x returns Some x if b is true and None otherwise.

flatten x is Some y if x is Some (Some y) and None otherwise.

append x y is the first element of the concatenation of x and y seen as lists. In other words, append (Some a) y is Some a, append None (Some b) is Some b, and append None None is None.

iter f x executes f y if x equals Some y. It does nothing otherwise.

iter2 f x y executes f z w if x equals Some z and y equals Some w. It does nothing if both x and y are None.

• raises Heterogeneous

  otherwise.

map f x is None if x is None and Some (f y) if x is Some y.

fold_left f a x is f a y if x is Some y, and a otherwise.

fold_left2 f a x y is f z w if x is Some z and y is Some w. It is a if both x and y are None.

• raises Heterogeneous

  otherwise.

fold_right f x a is f y a if x is Some y, and a otherwise.

fold_left_map f a x is a, f y if x is Some y, and a otherwise.

Same as fold_left_map on the right

cata f e x is e if x is None and f a if x is Some a

default a x is y if x is Some y and a otherwise.

lift is the same as map.

lift_right f a x is Some (f a y) if x is Some y, and None otherwise.

lift_left f x a is Some (f y a) if x is Some y, and None otherwise.

lift2 f x y is Some (f z w) if x equals Some z and y equals Some w. It is None otherwise.