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doc/batteries/BatReturn/index.html
Module BatReturn
Local exceptions/labels/goto/return.
This module defines a mechanism akin to SML's exception generators or to a generalization of C's return, i.e. the ability to define local labels, which may be used for immediately terminating an expression and returning a value. By opposition to usual OCaml exceptions, this mechanism
- allows polymorphic return values
- makes accidental exception catching slightly harder (while a local exception can escape its scope, it cannot be caught again by accident from this module).
Example:
let find_in_array a e =
label (fun label ->
for i = 0 to Array.length a - 1 do
if Array.get a i = e then return label (Some i)
done;
None)@documents Return
val label : ('a t -> 'a) -> 'alabel 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) -> 'alabel 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.
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.