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From: ka@socrates.hr.att.com (Kenneth Almquist)
Subject: Re: Why don't large companies use Ada?
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Date: Wed, 7 Dec 1994 05:46:46 GMT
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Date: 1994-12-07T05:46:46+00:00
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Michael Feldman <mfeldman@seas.gwu.edu> wrote:
> But unless I mis-read the post from the IBM chap the other day,
> ISUB does more than logically swap the indices, it actually
> transposes the array.

ISUB lets you declare an array which is really a veiw of another
array.  For example:

	DCL A_FORTRAN(5, 7);
	DCL A(7, 5) DEFINED A_FORTRAN(2SUB, 1SUB);

declares the array A_FORTRAN, and then overlays the array A on top
of it with the subscripts in the opposite order.  This means that
A(3, 2) refers to the same element as A_FORTRAN(2, 3).

Now you can write:

	DCL FSUB ENTRY((5, 7) FLOAT) OPTIONS(FORTRAN NOMAP);
	FSUB(A_FORTRAN);

The FORTRAN option tells the PL/1 compiler that FSUB is a FORTRAN
routine (probably unnecessary, but a good precaution), and the NOMAP
option tells the compiler to pass the arguments directly even though
the routine is in FORTRAN.  Without the NOMAP option, the PL/1 compiler
would create a copy of the array with the subscripts swapped.

> Has PL/1 supported ISUB all along? I do not remember it from my
> PL/1 days 20 or so years ago.

The information in this posting comes from a 1974 manual.
				Kenneth Almquist