Evaluation Of Algebraics - HP -28S Manual

The rules for evaluating names and evaluating programs lead to one
of the fundamental ideas in programming the HP-28S. For this dis-
cussion, "program" means a program storeq in a variable, and "name
of a program" means the name of the variable that contains a
program.
The fundamental idea is called
structured programming.
It means that a
complicated task is broken into subtasks, and a program is written for
each sub task. The main program can now be relatively simple, reflect-
ing the overall logic of the task. It can execute each subtask simply by
including the unquoted name of the program for that subtask. If a
subtask is executed more than once, the unquoted name can be in-
cluded more than once. If other main programs use the same subtask,
they can execute the subtask in the same way.
Structured programming is demonstrated in "Expanding and Collect-
ing Completely" on page 253, "Displaying a Binary Integer" on page
257, and "Median of Statistics Data" on page 270.
Evaluation of Aigebraics
Each algebraic is equivalent to a program that contains only unquoted
names and functions. Evaluating an algebraic produces the same re-
sult as evaluating the corresponding program: unquoted names are
evaluated, and functions are executed. This topic is also discussed in
"Evaluation of Algebraic Objects" in the Reference Manual.
The result of evaluating a name depends on the existence of a vari-
able with that name, as described in "Evaluation of Global Names"
above. Some examples:
• If a name refers to a user function, you can use the user function's
name like a built-in function. Evaluation of the algebraic causes
execution of the user function. The arguments to the user function,
enclosed in parentheses and following the user function's name, are
part of the algebraic.
202 23: Evaluation