CS 342 Lecture -*- Outline -*-

* environments and scope of declarations (contexts)

	<?> how do we know what the assignment "I = 27" means?
		have to know what I means, from its declaration (real vs. int)
	<?> what is the meaning of the declaration "INTEGER I"?
		establishes binding of I to an integer cell

** Environment
	mapping from identifiers to attributes (such as type, storage)
	(like symbol table discussed earlier)

	different environments in different parts of a program

-------------------
	PROGRAM MAIN
	INTEGER N
	...
	CALL Q(N,3)
	...
	END

	SUBROUTINE Q(M,L)
	REAL X
	...
	END
-------------------

** Visibility
	a *declaration* is visible if present in active environment
	-loosely, an identifier is visible if the current environment has
		some binding for that name


** Scope (of a declaration)
	area of program text where a declaration is visible
	show *contour diagram* for example
	subprogram arguments and variables *local* in FORTRAN
		(good because these details should be hidden from clients)
	scope of subprogram names is entire program, *global*

** Contour diagrams
	Show visibility of declarations (i.e., scope)
		(can see out but not into box)