Re: "procedure" vs. "function"

[J Martin Rushton]

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On 18/04/15 21:28, PMA wrote:
> J Martin Rushton wrote:
> 
> 
<snip>
> 
> FORTRAN also insists on the distinction (at least officially).  In 
> FORTRAN you CALL procedures as a single statement whereas you
> simply use functions in an expression.  If you try to mix them the
> compiler _ought_ to throw the syntax out.  Likewise BASIC
> distinguishes between GOSUB and invoking a function in an
> expression.
> 
> Consider writing a procedure to perform a task.  If this is invoked
> as a function then what is the return value?  It might be anything
> that was left in the register used to pass the value back; worse,
> if returning by reference then you could be interpreting random
> data as an address!  Modern compilers often trap this by zeroing
> the return value, but you can't rely on it.
> 
> You also need to keep in mind that the syntax checking of 2&  3
> GLs was not as extensive as modern languages like C/C++.  Pascal,
> in particular, was designed as a single pass language so that cards
> or tape could be read in, passed sequentially through the compiler
> and the object code stored to tape.  In the 1970s even mainframes
> often only had 128 KiB of memory.  Saving a few machine
> instructions may seem trivial today, but major programs were often
> only kibibytes in length in the 1960s.
>> 
>> _______________________________________________ lilypond-user
>> mailing list address@hidden 
>> https://lists.gnu.org/mailman/listinfo/lilypond-user
> Martin,
> 
> Thank you for this!   (And obviously after 40+ years, I have
> forgotten my BASIC.)
> 
> PMA

Getting a bit OT, but I've just had a quick look in my books.  Ada and
PL/1 also make the distinction, the former is possibly slightly
surprising given its object-orientated pretensions.  COBOL is
fascinating though, it has procedures, subprograms but no functions.
Procedures are unparametised blocks of code within the same
compilation unit accessed by a PERFORM statement.  To use a subprogram
you needed to write it as a separate compilation unit and invoke it
with CALL <subproc> USING <param> [...]

All in all it was a lot easier in machine code. ;-)
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