Paul Koning paulkoning at comcast.net
Fri Jan 29 13:07:54 CST 2021

> On Jan 29, 2021, at 12:12 PM, Chuck Guzis via cctalk <cctalk at classiccmp.org> wrote:
> On 1/29/21 6:27 AM, Paul Koning via cctalk wrote:
>> True, although right to left is not a natural way to read mathematical formulas.  The reason APL uses right to left is that the designers apparently were unwilling to change the direction of the assignment operator, so everything else had to follow.  Another language that doesn't have precedence avoided this issue by changing assignment to match the others, i.e., everything is left to right.  That is POP-2, a language out of the U of Edinborough I remember from an AI class.  So it would do stuff like:
>> 	a + 1 * 5 -> b
>> which in C would be
>> 	b = (a + 1) * 5;
>> and is definitely easier to read than the APL equivalent.
> Well, part of the confusion lies in the difference of "=" in mathematics
> indicating a property or state, as opposed to computer languages using
> it as an operator. It's a subtle distinction, but important.
> D = 4AC in mathematics establishes a property of D, whereas
> D = 4*A*C in BASIC, etc. means "multiply 4 by A, then take that result
> and multiply it by the value of C and store the result into D.
> APL treats the assignment as what it is--an operation.   Why the RTL of
> APL was chosen by Iverson, is a mystery; I agree.  He was, as far as I
> know, not  native writer of Hebrew.  I suppose we should be grateful
> that he didn't specify APL as a boustrophedon.

You're correct about equality or identity vs. assignment, but that wasn't my point.  I should have used ALGOL rather than C as the "other language" example to avoid introducing that angle.

Yes, the right to left thing is really strange, since it requires changing the usual order of hundreds of operators to preserve the usual order of a single one, rather than serving the majority as POP-2 does.

BTW, I don't really know Hebrew but doesn't it still write math LTR?  I know they write numbers that way.


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