force ( lazy -- value )

Vocabulary

lazy

Inputs

lazy

a lazy

Outputs

value

an object

Word description

Calls the quotation associated with the lazy if it has not been called before, and returns the value. If the lazy has been forced previously, returns the value from the previous call.

Definition

USING: accessors combinators continuations kernel ;

IN: lazy

: force ( lazy -- value )
    dup status>> {
        { +error+ [ value>> throw ] }
        { +value+ [ value>> ] }
        {
            +unforced+
            [
                [ f ] change-quot swap [
                    ( -- value ) call-effect
                    [ >>value +value+ swap status<< ] keep
                ] curry
                [ [ >>value +error+ swap status<< ] keep throw ]
                recover
            ]
        }
    } case ;