Thanks for that Joe. That helps a lot.
If I want general-to-particular reading order, must I define a parsing word
of my own?
Stack efficient order:
b negated 1/2a * :> -b/2a
Context efficient order (general-to-particular perception and reasoning):
-b/2a <: b negated a/2 *
(Yes, I made up my own long forms of recip, neg, and sq. )
That last form is like a traditional assignment statement. How then do I
write the definition for
<:
?
Shaping
From: Joe Groff [mailto:[email protected]]
Sent: 2010-November-09, 21:38
To: [email protected]
Subject: Re: [Factor-talk] Furnace, XStreams (PEGs) and some observations
about Factor
On Nov 9, 2010, at 2:08 PM, Shaping wrote:
I'm hungry for local variables, now, though this goes against much of the
basis of stack languages. I want lexical forms I can read and understand
(parse with my mind, left-to-right, and down in a tree) to produce a known
result (not a best guess). I don't want to remember a lot of stuff, because
human memory is fragile and ultimately limits all programmers. I know that
we have a "locals" vocab of some kind, but don't know how to use it. Is
anyone using locals a lot in Factor just for readability? Can locals be
used efficiently for the machine, too? How can locals be abused?
Locals are used all over the place, and suffer no performance penalty. Don't
worry about using them, or "going against the basis of stack languages."
Practicality beats purity. Often, after writing something out with locals,
it makes the concatenative approach clearer.
You can bind local variables by using the "::" definition form, which binds
the function's input values to lexical variables:
:: add ( x y -- z ) x y + ;
Within a :: definition, you can bind additional variables off the top of the
stack with the ":>" operator:
:: quadratic ( a b c -- x1 x2 )
2 a * recip :> 1/2a
b neg 1/2a * :> -b/2a
b sq 4 a c * * - sqrt 1/2a * :> disc/2a
-b/2a disc/2a +
-b/2a disc/2a - ;
-Joe
------------------------------------------------------------------------------
The Next 800 Companies to Lead America's Growth: New Video Whitepaper
David G. Thomson, author of the best-selling book "Blueprint to a
Billion" shares his insights and actions to help propel your
business during the next growth cycle. Listen Now!
http://p.sf.net/sfu/SAP-dev2dev
_______________________________________________
Factor-talk mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/factor-talk
