> Implement
>
> BlockClosure>>valueWithExit
>     ^self value: [^nil]

In the visitors of Pier I use a similar pattern to jump to certain
states in the visitor. In Scheme this pattern is commonly done using
continuations, but since I always jump upwards the stack it is more
efficient to use blocks in Squeak.

Object>>withEscaper: aBlock
    ^ aBlock value: [ :value | ^ value ]

Then you can then do something like:

self withEscaper: [ :break |
    aCollection do: [ :each |
        self withEscaper: [ :continue |
            ....
            ... ifTrue: [ break value: result1 ].
            ... ifFalse: [ continue value: result2 ].
            .... ] ]

Cheers,
Lukas

-- 
Lukas Renggli
http://www.lukas-renggli.ch