Re: Algol history, was specifying semantics

Ivan Godard <ivan@ootbcomp.com> wrote:
>> [As far as I know, the machine readable source was lost.
>> Even with a copy of the source, you'll need a copy of PL360, the
>> Algol-flavored assembler it was written in. -John]


> IMO, PL360 was the best language work that Wirth ever did.


(snip)


> The key idea was the absence of operator precedence; expressions were
> executed in strict left-to-right order, with operations for each machine
> op and explicit register names for operands:


> r5 := r3 + r2 * r1; (PL360)


> The target register served as the accumulator for the expression.


It gets even more interesting, as I remember it, if the left side
register is also on the right. Consider:


      r1:= r1 + r1 + r1;


which, in effect, multiplies r1 by four. As you note, r1 is the
accumulator for the expression, and also changes as it is being
evaluated:


        LR R1,R1
        AR R1,R1
        AR R1,R1


Remembering from 40 years ago, I believe that one is in the manual.


-- glen

Return to the comp.compilers page.
Search the comp.compilers archives again.