.Open CS320/12 Implementing Subprograms (Chapter 10)
.Table
.Row Prev 11	LISP    Chapter 2 section 4 +  LISP handout     lab11 LISP101
.Row 12	Implementing subprograms        Chapter 10   lab12 LISP102
.Row Next 13	Functional  Programming	Chapter 15  not section 8       lab13 LISP103
.Close.Table
. Preparation
Study the  $Notes below.

Sudy Chapter 10.

Think about the $Notes and the reading.

Answer the chapter's review questions.

Hand in answers to 2 or more review questions.

.Open Notes

(1) You need to describe the activation records for several kinds of language.

(2) You need to describe the activation records for several kinds of language
using the UML.

(3) Variables declared in a C program can be global - visible to all parts
of the program, or local to a file (static external), or be local to a 
particular block. A subprogram can only be local to a file or global. So, 
functions are never declared inside another function and so the referencing
environment of functions can never contain variables that are local to 
other functions. This means that the compiler does not need to keep track 
of them. It lets the linker handle global variables and functions. So C has
simpler Activation Records than Algol or Pascal.

(4) In nearly all modern languages data is stored in two places: the
.Key stack
and the
.Key heap
The data on the stack is created (pushed) and
deleted(popped) automatically as the blocks and subprograms are entered
and exitted, respectively.  However, data on the heap is
created by special explicit operators like the "new" operator in
Java and C++.  It continues to exist after the subprogram or block
in which it was created terminates.  It is accessed indirectly by
a pointer.  If all the pointers to a piece of heap data are deleted
then the data becomes garbage -- it takes up space that can be recycled.
Java automatically 
.Key collects the garbage
and lets the program reuse the memory space.  C++ does not -- and the
programmer must do it themselves.

.Close
. Class Work
.See ./12q.html

. Lab Work -- More LISP
.See ./lab/12.html
. Next -- Functional Programming
.See ./13.html