Am 17.07.2019 um 19:54 schrieb Paul Gilmartin:
On Wed, 17 Jul 2019 12:22:35 -0400, Steve Smith wrote:
The original sin was making "=" the assignment operator. I guess we can
blame that on FORTRAN, and it must make mathematicians cringe still.
I once (ca. 1967) needed to enlighten and disillusion a naive
but persistent physics graduate student who had coded in what
he believed was FORTRAN something akin to:
B( 1 ) = X( 1 ) * 1 + X( 2 ) * 2
B( 2 ) = X( 1 ) * 3 + X( 2 ) * 4
B( 1 ) = 3.14
B( 2 ) = 2.718
PRINT X( 1 ) X( 2 )
...
expecting to solve a system of linear equations, apparently assuming
that "=" was not assignment but a sort of identity declaration. I.e.
determine the values of X() that satisfy all the "equations". I can
barely imagine the number of false starts he needed to circumvent
syntax errors before he approached me for counsel.
-- gil
This reminds me of a similar story :-)
I wrote a PL/1 parser for a customer of mine some years ago;
the idea was to detect some logic errors and flag some language constructs
which the customer did not want (not allowed by site standards); and to
issue
warnings on some constructs which the compiler at that time couldn't.
There were several thousand sources to be checked, because it was a
large company.
About 10 percent of the programs had some sort of issue.
One program had a coding like this:
IF 9 < ZZ < 20 THEN DO;
...
this was flagged by my parser; it complained because a BIT value
(9 < ZZ) is compared with a numeric value (20). The PL/1 compiler
didn't say anything, no error or warning.
Obviously this is not what the coder intended; the coder must have had
a mathematics background. He (or she) apparently asked for
IF (9 < ZZ) & (ZZ < 20) THEN DO;
...
The original coding is always TRUE, BTW. ('0'B and '1'B are both < 20).
This error has not been detected for more than 20 years :-)
and IMHO in this case again the problem is the PL/1 language definition,
because it allows all these implicit type conversions, even very strange
ones.
Kind regards
Bernd
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