Get two kinds of essentially nesteddescendancy, static (from the source code) and dynamic from execution as make calls but from which have not yet returned. It's good to think about both at the same time. The push down stack of dynamic descendancy defines what parts of the code are active and, thus, can be called. E.g., the names currently known by inheritance are from the dynamic descendancy working through the static descendancy. And, then, can call code back in dynamic descendancy that is still known from the static descendancy.
Wow! It's simpler than that: Can have BEGIN-END as a chunk of code with its own names. Any name used inside there but not declared there is inherited from the code that is active (in dynamic descendancy) and in the static descendancy.
E.g., can have ON CONDITION X; BEGIN; ... END; and execute that. That execution just says that, in the future, if see RAISE X, then execute the code in the BEGIN-END. Then that code can do GOTO Y where Y is a label known in the BEGIN-END block and in code in the dynamic descendancy. If the code of Y is 11 steps back in the stack from the RAISE, then all the 10 lower levels of code are exited. Lots of cleanup happens automatically.
So, the ON CONDITION is executing code back in the stack of dynamic descendancy -- darned cute. And can do such things quite generally.
So, code block A can have an internal subroutine B, call C, pass an entry variable to B, and the code of C can call B. B then can have values inherited from the code of A and use those values as B executes from the call of C. Did that once when scheduling the fleet for FedEx!
Once in some AI work at IBM's Watson lab, used a fancy case of that name scoping to save our project a few weeks of work and improved the quality of our product. Got an award for that!
That's a fast outline -- maybe not fully clear. Any questions?
At times I've thought that that little device (pattern?) was essentially a closure, but since I don't really know what a closure is I can't really say!
Uh, I've done a lot of programming in a lot of languages, but my main interest is not as a programmer but as a founder of a startup that needs some software!
Wow! It's simpler than that: Can have BEGIN-END as a chunk of code with its own names. Any name used inside there but not declared there is inherited from the code that is active (in dynamic descendancy) and in the static descendancy.
E.g., can have ON CONDITION X; BEGIN; ... END; and execute that. That execution just says that, in the future, if see RAISE X, then execute the code in the BEGIN-END. Then that code can do GOTO Y where Y is a label known in the BEGIN-END block and in code in the dynamic descendancy. If the code of Y is 11 steps back in the stack from the RAISE, then all the 10 lower levels of code are exited. Lots of cleanup happens automatically.
So, the ON CONDITION is executing code back in the stack of dynamic descendancy -- darned cute. And can do such things quite generally.
So, code block A can have an internal subroutine B, call C, pass an entry variable to B, and the code of C can call B. B then can have values inherited from the code of A and use those values as B executes from the call of C. Did that once when scheduling the fleet for FedEx!
Once in some AI work at IBM's Watson lab, used a fancy case of that name scoping to save our project a few weeks of work and improved the quality of our product. Got an award for that!
That's a fast outline -- maybe not fully clear. Any questions?