I sometimes find, when working with a stream, that I need to "peek ahead��� a few items, without disturbing the state of the stream. The message stream peek gives me the next item, but doesn���t generalize to multiple items,   So I end up writing code like this:

    findSomething
| savedPosition result |
savedPosition := stream position.
stream position: start.
���code involving various manipulations of stream, including stream next"
result := stream position + 1.
stream position: savedPosition.
^ result

This code involves at least two temps, is not very easy to read, and risks not resetting the stream properly if I do a return.

It seems to me that a better solution would be what Kent Beck calls an ���execute around��� method:

    findSomething
^ stream unchangedDuring: [ :s |
���code involving various manipulations of stream, including stream next"
stream position + 1 ]

I���m not sure that I like the name #unchangedDuring:; perhaps you can think of a better one? 

The  implementation of this would be

PositionableStream >> #unchangedDuring: aBlock
"execute aBlock with self as argument. Ensure that when this method returns,
I still have my current state."
| savedPosition |
savedPosition := self position.
^ [ aBlock value: self ] ensure: [ self position: savedPosition ]

or perhaps

PositionableStream >> #unchangedDuring: aBlock
"execute aBlock with self as argument. Ensure that when this method returns,
I still have my current state."

^ [ aBlock value: self copy ]

which might be better in the case that the stream is a file stream and aBlock causes the buffer to be refreshed from the disk.