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iql-documentation/call.mem
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CALL
FUNCTION: Allows IQL to call a separately written user own-code
program, to pass parameters to the user program, and
to process parameters passed back from the user
program.
FORMAT:
CALL nn [=]item1, [=]item2,...
DISCUSSION:
1) The CALL capability lets you extend the
capabilities of IQL by incorporating your own logic.
This is a sophisticated use of the system. While
laymen may use the CALL command to drive user
programs that have been linked with IQL, only
professional programmers should attempt to add a
capability to IQL by writing their own-code and
linking it into IQL.
2) Up to eleven (11) items - which may be data items,
variables, constants or literals - may be passed to
the user program. These items may be any mix of type
alphanumeric, numeric or binary.
3) If you prefix a passed parameter with an equal
sign (=), it means that the user program will pass
back a new value for that item. Upon returning from
the user program, IQL will put the new value in the
named item. You may not use = before constants or
literals in the CALL statement.
4) The integer, nn, in the CALL statement is called
the 'call number' and is passed to the user program
which uses it to determine which entry has been made
(if there are multiple type entries). For instance,
a query might do CALL 10 =X to calculate a sine, and
CALL 20 =X to calculate a tangent - the user program
would determine what to do depending on whether it
saw a 10 or 20 as the call number.
5) The user program may pass back a status value in
the special item ERROR-STATUS. You may test
ERROR-STATUS in your query just by refering to it.
See the example.
6) You may use as many CALL statements, which may use
the same or different call numbers, as you need in a
query.
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CALL
continued
7) The user program must have the entry point IQCALL.
Becauser a dynamic loader is not available, the user
program must have been linked with the IQL execution
module, IQE and saved before you can run a query that
calls it. Generally you will have done this in your
directory or PPN so that you have a special version
of the execution module. IQL always executes a
module in your directory or PPN rather than a module
elsewhere (ie in SYS:). Please see the instructions
on the IQL installation tape for how to link and save
the IQE module.
8) IQL is delivered with a dummy IQCALL module linked
in; if you use CALL on the delivered IQL version,
the arguments you pass will be listed out and control
will be returned to IQL.
9) The formats of the arguments passed by CALL to the
user program are:
01 PASSED-PARAMETERS USAGE IS DISPLAY-6.
02 CALL-NUMBER PIC 999.
02 ERROR-STATUS PIC XXX.
02 PARAMETER OCCURS 11 TIMES.
04 ALPHA-PARAM PIC X(30).
04 REDEF1 REDEFINES ALPHA-PARAM.
06 FILLER PIC X(12).
06 NUMERIC-PARAM PIC S9(18).
04 REDEF2 REDEFINES ALPHA-PARAM.
06 FILLER PIC X(18).
06 BINARY-PARAM PIC S9(18) COMP.
Note that the argument parameters are redefined three
ways - one to hold alphabetic passed values, one to
hold numeric passed values, and one to hold binary
passed values. The user program should refer to the
parameter type that matches the item IQL was told to
send. Item types may be mixed in IQL CALL
statements.
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CALL
continued
EXAMPLES:
In the first example, we go to a user routine to
calculate each employee's witholding pay based on
dependents, salary (ie tax bracket) and year-to-date
pay.
HEADING 'CALCULATION OF WITHOLDING AMOUNT'.
OPEN PAYROLL.
CALL 10 SALARY DEPENDENTS YTD-PAY XWITHOLDING.
IF ERROR-STATUS NOT = 'AOK' PRINT '**ERROR**'.
PRINT EMPNO,NAME, SALARY, XWITHOLDING.
In the second example, we go out to a user routine
twice to get some trigonometric functions so we can
calculate, from the height of the building and an
angle from the ground, the distance to the base of
the building (XLEVEL) and how long a rope (XSLANT) it
would take to reach the top of the building. In each
case, the answer is returned in a numeric variable
which we then use in a calculation.
HEADING 'DERIVED DISTANCES'.
TITLE XLEVEL = 'LEVEL//DISTANCE'.
TITLE XSLANT = 'SLANT//RANGE'.
OPEN BUILDING FILE.
CALL 3 ANGLE =XTANGENT.
COMPUTE XLEVEL = HEIGHT / XTANGENT.
CALL 1 ANGLE =XSINE.
COMPUTE XSLANT = HEIGHT / XSINE.
PRINT ANGLE, HEIGHT, XLEVEL, XSLANT.