On 19 November 2013 16:33, gettimothy <gettimothy at zoho.com> wrote:
> Part 4 of the Blue Book--chapter 26 The implementation--in the intro there
> is this example:
>
>
>
> center
>   ^ origin + corner / 2
>
>
>
> With these operations
>
>
> Rectangle center
>   0       push the value of the receiver's first instance variable (origin)
> onto the
>           stack
>    1       push the value of the receiver's second instance variable
> (corner) onto the
>           stack
>   176     send a binary message with the selector +
>   119     push the Smalllnteger 2 onto the stack
>   185     send a binary message with the selector /
>   124     return the object on top of the stack as the value of the message
> (center)
>
>
> In a Workspace, when I doit on 3 + 7/2 I get 5, left, right, unary,
> binary....rules apply.

Yep, because "message sending is all there is", which equates here to
a lack of operator precedence. So "3 + 7/2" means "(3 + 7) / 2".

+ and / here are known as binary selectors.

> What I see here--and please check my reasoning--is a RPN that places things
> onto the stack via Smalltalk's order of operation rules and then does
> conventional RPN processing.

More generally, keyword sends take precedence over unary sends which
take precedence over binary selectors. So in

foo something: 1 + 2 negated with: bar

the #negated message will be sent to the object 2,
that will be the argument of the #+ message, sent to the object 1,
and then that result and the object bar will be the arguments of the
#something:with: message to the foo object.

frank

> In other words, Smalltalk expressions are translated to RPN and then placed
> on the stack.
>
> A simple 'banish the thought' or 'yep' or 'sometimes'  would be helpful as I
> move forward in my study.  I am just trying to avoid carrying forward an
> improper idea that I will have to revise later when/if the facts turn out
> otherwise.
>
> thx.
>
> t
>
>
>