On Wed, 21 Jan 2015 15:01:28 +0100, Bernd Oppolzer wrote:
>...
>No, the things I had in mind was the assignments including increment etc,
>the things like A += expression; etc ... works with other kinds of
>operators, too, of cours, not only addition.
> ...
But beware if you expect similar behavior from A <= expression.
>>> BTW: variable ++; is not still possible in PL/1 for several good reasons.
>>>
>> I'm naive. What's a good reason (other than economy of language design)
>> for not providing "variable ++"? (And what of "++ variable"?) One
>> possibility might be lexical ambiguity.
>
>Some speculation on my part:
>
>in C, everything is an expression;
>a ++ and ++ a are two very different expressions,
>and this idea does not fit well into the PL/1 spirit.
>
I guess I'm not a true believer. Yes, the ++ and -- operators
have a side effect of modifying their operands. I don't find this
particularly objectionable.
"Ontogeny recapitulates phylogeny." A possible motivation for
providing ++ and == as operators is that they were hardware
instructions on some (early) computers. But not s/360, so they're
absent from PL/I.
Regrettably, in C not everything is an expression. I often wish
I could use a block as an expression:
V = { int I; ... }
In Algol 68 a procedure declaration is merely an instance of use of
a block as an expression.
>The assignment a += 5;
>in C is an expression, too (and may be assigned to other variables
>and used, whereever expressions are allowed in C).
>
>But it is no problem to take this kind of syntax over to PL/1,
>WITHOUT assigning a value to the assignment A += 5;
>(that is: without violating the language).
>
Has PL/I no operators which modify their operands?
>a = b = c;
>
>in C.
>
And, peculiarly, in Algol 68 "V := expression" is itself an expression with
a value with value not "expression" but the L-value of V.
-- gil
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