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From: anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups: comp.arch
Subject: Re: Why VAX Was the Ultimate CISC and Not RISC
Date: Wed, 12 Mar 2025 08:57:19 GMT
Organization: Institut fuer Computersprachen, Technische Universitaet Wien
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Lawrence D'Oliveiro <ldo@nz.invalid> writes:
>One of the early programming languages I came across was POP-2. This was 
>fully dynamic and heap-based, like Lisp, but also had an operand stack. So 
>a simple assignment statement looked like
>
>    a -> b;
>
>but this could actually be written as two separate statements:
>
>    a;
>    -> b;
>
>The first one pushed the value of a on the stack, the second one popped it 
>off and stored it in b.
>
>This made it easy to do things like swap variable values:
>
>    a, b -> a -> b;

In Forth you can define VALUEs that work like these POP-11 variables.
In standard Forth you can write

3 value a
5 value b
a b to a to b \ swaps the contents of a and b
a . b . \ print a and b

In some Forth systems you can write it in a syntax even closer to that
of POP:

On VFX Forth you can write:

a b -> a -> b

In Gforth (development version) you can write

a b ->a ->b

That's all not very idiomatic, though.  VARIABLEs (which push their
address rather than their value) are more popular than VALUEs, but
usage such as the following is also not idiomatic; you usually use
variables (and values) sparingly.

variable a 3 a !
variable b 5 b !
a @ b @ a ! b !
a @ . b @ .

- anton
-- 
'Anyone trying for "industrial quality" ISA should avoid undefined behavior.'
  Mitch Alsup, <c17fcd89-f024-40e7-a594-88a85ac10d20o@googlegroups.com>