Re: rant // OE scope \\ forked out of 500 Rosetta
- Posted by _tom (admin) Apr 20, 2017
- 1534 views
I wonder if "line of sight" might be a more appropriate metaphor.
...
Paradoxically, scopes can be difficult to describe and/or understand, precisely because they are inherently obvious.
Pete
Physical models don't quite work with scope. But, the "line-of-sight" model has promise.
Line-of-sight
When you write a computer program it looks like this to you:
atom x = 0 atom sum = 0 while 1 do x += 1 sum += x if x > 5 then exit end if end while ? sum --> 21
When you look a a landscape what you see is something like this:
................................... horizon (end of space)
^
^
/ \
|
^
/ \
/___\
|
^
/ \
/ \
/ \
/ \
________
|
0
-|-
/ \ you, looking at a landscape full of trees
What the same program looks like to an interpreter is:
-- look towards the horizon
^ all the way to end of space
? sum │
end while │
if x>5 then exit end if │
sum += x │
x += 1 │
while 1 do │
atom sum = 0 │
atom x = 0 -- you can "see" x here ---┘
"x" does not exist yet, you can't see it, out-of-scope
--start here
An identifier does not exist until you make a declaration; if it does not exist you can not see it.
If the Interpreter can "see" it then it is "ok", things are in-scope and things work. If the Interpreter can not "see" an identifier, then it is out-of-scope and it crashes.
The "line-of-sight" model should work for a lot of people (if their mind is flexible enough to to flip things about).
_tom
