Re: modifying constants in Fortran and elsewhere

On 7/15/23 12:57 PM, Thomas Koenig wrote:
> gah4 <gah4@u.washington.edu> schrieb:
>> A potential bug since the earliest days of Fortran is passing a
>> constant to a subroutine, and then changing the value of the dummy
>> argument.


> I actually got bitten by that while using a mainframe for scientific
> work as a student. It's been a few decades, so I don't recall too
> many details. It was difficult to find, but I was paid by the hour,
> so I didn't mind too much :-)


I remember such a bug in the 80s on the pdp-11/34 of our institute.




> Algol 60 tried to define
> its argument passing in an elegant way, and accidentally invented call
> by name when they meant call by reference. -John]


By Name example from the German wikipedia
<https://de.wikipedia.org/wiki/Namensparameter>


  >>
A[1] := 10
A[2] := 20
i := 1
x := Funkt (A[i], i)


FUNCTION Funkt (a, i) : Real
      i := i+1
      RETURN a
END


x wird der Wert 20 zugewiesen. Im Werteparameter-Fall wäre x dagegen 10,
ebenso bei Referenzparametern.
<<
Returns 20 as ByName while 10 were returned for ByRef.


DoDi
[Then there's the infamous Knuth Man or Boy program, where even he
couldn't figure out what the answer was supposed to be.
https://en.wikipedia.org/wiki/Man_or_boy_test
-John]

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