Re: question regarding multiple-value-bind

[Johann Petrak <johann@mail4.ai.univie.ac.at>]

> when i execute the following i get this error.
> (multiple-value-bind (x y) (values 1 2) (return nil))
>  
> *** - RETURN-FROM: no block named NIL is currently visible
> 1. Break>
> could someone explain why this is a error?
Why shouldn't it be? There is no block around the return and therefore
no return can be used. The multiple-value-bind will return the last value
after the values-form, so
(multiple-value-bind (x y) (values 1 2)) ==> nil
(multiple-value-bind (x y) (values 1 2) y) ==> 2
etc.

To use return, use block, or do it inside one of the forms that
implicitly create a block named nil:

(block nil (multiple-value-bind (x y) (values 1 2) (return nil))) ==> nil

Johann Petrak                            Email: johann@ai.univie.ac.at
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