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Trailing-Edge - PDP-10 Archives - BB-H548B-BM - 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.
                                                             Page 2


                                                            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.
                                                             Page 3


                                                            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.