`type 'a t`

A label which may be used to return values of type `'a`

`val label : ('a t -> 'a) -> 'a`

`label f` creates a new label `x` and invokes `f x`. If, during the execution of `f`, `return x v` is invoked, the execution of `f x` stops immediately and `label f` returns `v`. Otherwise, if `f x` terminates normally and returns `y`, `label f` returns `y`.

Calling `return x v` from outside scope `f` is a run-time error and causes termination of the program.

`val with_label : ('a t -> 'a) -> 'a`

as `label`

`val return : 'a t -> 'a -> _`

Return to a label. `return l v` returns to the point where label `l` was obtained and produces value `l`.

Calling `return l v` from outside the scope of `l` (i.e. the call to function `label` which produced `l`) is a run-time error and causes termination of the program.