Hi!

If your collection understands #readStream, you may write:

Puzzle >> blockIterating: aCollection

    ^[ :doBlock :whileBlock |
        | stream item |
        stream := aCollection readStream.
        [ stream atEnd not and: [
            whileBlock value: (item := stream next) ] ] whileTrue: [
                 doBlock value: item ] ]

If it only understands #do:, you may wrap it in a Generator:

Puzzle >> blockIterating: aCollection

    ^[ :doBlock :whileBlock |
        | stream item |
        stream := Generator on: [ :g |
            aCollection do: [ :each | g nextPut: each ] ].
        [ stream atEnd not and: [
            whileBlock value: (item := stream next) ] ] whileTrue: [
                 doBlock value: item ] ]

If it's not a requirement to return a Block, you may create a class,
whose instances respond to #value:value: and sidestep the problem.

Cheers, Balázs
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