[racket] Pass by value/name/reference

On Jul 20, 2014, at 9:25 PM, Jon Zeppieri wrote:

> On Sun, Jul 20, 2014 at 6:27 PM, Matthias Felleisen
> <matthias at ccs.neu.edu> wrote:
>> 
>> The phrase "call-by-value is a reduction strategy" has no meaning per se but is a left over from the time when people hadn't figured out the above (pre 1070).
>> 
> 
> I apologize for spreading this nonsense. Is it the phrase "reduction
> strategy" that's the problem? In the paper you cited, you refer to
> "evaluation strategies" and "binding strategies" and list
> call-by-value (eager) and call-by-name (delayed) as examples of the
> former. Is the problem with "reduction strategy" that it properly
> refers to rules for reducing redexes in a lambda calculus (and not
> parameter-passing in a programming language)? Or is it just nonsense
> tout court?


Yeap. Strategies exist in any LC. A strategy is simply a function
that picks the next redex to reduce. Strategies have uses BUT not 
to describe parameter-passing mechanism. The latter are turned into
axioms directly. For example

 BY NAME: (function (x) body) any-argument = body with all (free) x replaced by any-argument
 BY VALUE: (function (x) body) value-argument = body with all (free) x replaced by value-argument

So you see there are two calculi and they each come with a different 
axiom but the SAME strategies. 

;; --- 

The idea is so much ingrained in programmer's mind due to some 
basic text books that I can't blame anybody and I am certainly
not blaming you. 

I just don't like it that the idea is repeated 40+ years 
after it was debunked in my neighborhood :-) 

-- Matthias