Instruction manual

USER GROUP NEWS
Issue 3 - Vol 2
MDP PRODUCT INFORMATION
BROAD BUT NOT A LHvIITING LIBRARY SET
LIBRARY ELEMENTS MAY BE EASILY REPLACED WITH ELEMENTS ~10RE FOCUSED ON
THE NEEDS OF THE PROJECT.
The following text describes the Rational language interface to the Modular Development Language.
RATIONAL
LANGUAGE DESCRIPTION
Rational is MDL/u except for one aspect. Since control flow is central to any program, regardless of the
specific application, the primary task for Rational is to conceal this part of MDL/u from the user, by producing
decent control flow structure.
THE IF STATEMENT
The standard construct. if a condition is true, do a group or things for example
if (x > 100)
{print" error: x > 100" ; err= I}
can't be implemented directly in MDL/u. Instead a programmer must translate this relatively clean thought
into MDL/u as follows:
10 IF (NOT (x > 100)) THEN 40
20
PRINT" ERROR: x > 100"
30 err = 1
40
When a program doesn't work, or when it must be modified, this must be translated back into a clearer form
before one can be sure what it does.
RATIONAL eliminates this error-prone back-and-forth translation. A group of statements can be treated as a
unit by enclosing them in braces" {" and"}" in Rational. This is true throughout Rational: wherever a single
statement may be used, there can be several enclosed braces.
Rational is a tree tormat language: statements may appear anywhere on a line, and several may appear on one
line if they are separated by a semicolon.
THE ELS E CLAUSE
Rational provides an else statement to handle the construct ir a condition is true, do this thing, otherwise
do that thing.
if (a<b)
{sw=O; print a, b}
else
{sw=l; print b,a}
This writes out the smaller of a and b, then the larger, and sets sw appropriately. The syntax ot the if statement
IS
if (legal MDL/u condition)
Rational statement
else
Rational statement
where the else part is optional.
December 1983
TEKTRONIX
5