A SELF 'program' consists of live objects
- No edit/run mode: just change the object directly.
- Smallest unit of exchange is a set of logically related changes: a module.
- Extra information must be supplied by the programmer.
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A SELF `program' consists of live objects
Self has no edit/run mode. To change an object, you do not retreat to a
source file, or even to a class, you just change the object itself. This was a major
design aim of the Self system. However, this stance creates a big problem
the moment you want to give your work to somebody else. You could give them a
snapshot, but how do they combine your work with theirs? There needs to be some
way to separate a `program' from a snapshot.
For Self, we take the view that the smallest unit which can be usefully
communicated to someone else is a set of logically related changes to a
Self system that provides the functionality required for a new
`application.'
How are these changes identified and communicated? We do not want to have
every change to every object become part of a new program, as this would be
unwieldy, causing unnecessary state to be saved. Instead, the programmer should
identify which changes to the system are logically related. A set of logically related
changes is called a module. We will shy away from the term `program' as it has
many unwanted connotations.
The programmer also needs to communicate how these changes should be applied
in a new system. For example, suppose an object contains a slot with 1024 in it.
Should that value be copied literally? Perhaps it is the result of some computation
(such as the width of the current screen) and should be recomputed instead. There
simply is not enough information in a Self object to extract a module
completely automatically from a snapshot, and the programmer must
communicate her intent occasionally.
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