Module Option

module Option: sig .. end

val is_some : 'a option -> bool

Does an option contain a value?

• Ensure is_some (Some x)
• Ensure not (is_some None)

val is_none : 'a option -> bool

Does an option contain no value?

• Ensure not (is_none (Some x))
• Ensure is_none None

val value : 'a option -> 'a

The value contained in an option.
Raises Invalid_argument when applied to None.

• Ensure value (Some x) = x

val default : 'a -> 'a option -> 'a

The value contained in an option, or a default if there is none.

• Ensure default d (Some x) = x
• Ensure default d None = d

val classify : ('a -> bool) -> 'a -> 'a option

Classify a value by placing it in an option.

• Ensure p x = (classify p x = Some x)
• Ensure not (p x) = (classify p x = None)

val perform : ('a -> unit) -> 'a option -> unit

Perform a command on the value in an option.

apply c (Some x) does c x, while apply f None does nothing.

val map : ('a -> 'b) -> 'a option -> 'b option

Map a function over the value in an option.

• Ensure map f (Some x) = Some (f x)
• Ensure map f None = None

val filter : ('a -> bool) -> 'a option -> 'a option

Filter the value in an option.

filter p (Some x) is Some x when p x holds and None otherwise, while filter p None is None.

val flatten : 'a option option -> 'a option

Flatten a doubly optional value.

• Ensure flatten (Some x) = x
• Ensure Flatten None = None