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From: Rod Pemberton <NoHaveNotOne@bcczxcfre.cmm>
Newsgroups: comp.lang.forth
Subject: Re: NAME! and NAME@ versus !NAME and @NAME
Date: Thu, 11 Feb 2016 05:02:07 -0500
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On Thu, 11 Feb 2016 10:01:25 +0100
Lars Brinkhoff <lars.spam@nocrew.org> wrote:

> Leo Brodie's Forth style guide says:
>=20
>   save value of (to stack)          @name
>   restore value of                  !name
>   store into                        name!
>   fetch from                        name@
>=20
> I don't understand when it's appropriate to use @name or !name, and
> when to use name@ or name!.
>=20
> My research so far: The Standard use the latter a lot: C!, 2! R@, F!,
> DEFER@, etc.  But the former seems to be rare.  I found !CSP and !BITS
> in some traditional Forths.  Machine Forth use A!/A@ to access the
> contents of the A register, and !A/@A to access memory.
>=20
> Any insights?


Leo Brodie's "Thinking Forth" pg 287

Meaning            Form    Example
...
save value of      @name   @CURSOR
restore value of   !name   !CURSOR
store into         name!   SECONDS!
fetch from         name@   INDEX@
...

=46rom that, my guess is that if the source
is the data stack and destination is a variable,
then the @ and ! come after and vice-versa.
I.e., @name and !name are expected to be paired
operations and so are name! and name@.

a) variable -> data stack -> variable
b) data stack -> variable -> data stack

Of course, as you can see they are equivalent.
It's just a matter of the the expected source.


Rod Pemberton