Vax 613 0S Instruction Manual download pdf (Page 12)

MDP

PRODUCT

INFORMATION Issue 3 - Vol 2

USER

GROUP

NEWS

THE

RETURN

STATEMENT

The

standard

MDL/u

mechanism for returning from

a.

function or procedure

is

to

branch to either

prend

or

frend.

If a value

is

returnable by a function

it

must first be assigned

to

the function name and the

branch

to

frend.

The

Rational

return

statement

provides these runctions.

For

example

deffn

fact (arg)

if

(arg<=l)

return

(1)

else

return (fact(arg-l)*arg)

fnend

produces the

MDL/u

source

10

DEFFN

FACT

(ARG)

20

IF

(NOT

(ARG<=l))

THEN

50

30

FACT=1

40

GOTO

70

50

FACT

= FACT(ARG-l)*ARG

60

GOTO

70

70

FNEND

In the case of a procedure a

return

does the following:

defpr proc( arg)

return

pread

generates this

MDL/u

source

10

DEFPR

PROC(ARG)

20

xx

GO

TO

xx+l

xx+l

PREND

The last

statement

in either a function or procedure

must

be a

return.

DEFINE

STATEMENTS

Any string of alphanumerics can

be

defined as a name; thereafter, whenever

that

name occurs in the

input

it

is

replaced with rest

of the line.

define

is

usually used to create symbolic parameters:

define MAXLEN 256

INCLUDE

STATEMENT

The

Statement

include test.r

inserts the contents

of

the

file

test.r

into

the

Rational

inpllt

in place of the include statement.

8

TEKTRONIX

December 1983

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