Re: On procedures within procedures

[Thien-Thi Nguyen]

() Mike Gran <address@hidden>
() Wed, 3 Apr 2013 07:04:43 -0700 (PDT)

   Do you have a personal philosophy on how much you try to
   minimize the scope of procedures?

I figure out the data structures first, then use procedures w/o
overmuch regard to inner/outer.  However, i...

   If you were writing a tutorial, what would you say?

...do try to keep to a minimum the number of arguments that are
passed from a procedure's caller to procedures it calls.

For example, in SGF Utils 0.6 src/render.scm, the procedure
‘make-screen-1’ is almost 700 lines long w/ 90 internal
procedures, the deepest being 6 levels (at least, depending on
what you count, precisely) from top.  This particular proc, i.e.,
‘make-screen-1 ray! one! poly-vecs two-side normal’:

 (define (two-sides actually)
 
   (define (normal direction)
     (make-polar radius (+ a (* (/ PI 2) direction))))
 
   (let-values (((mx my) (actually (normal -1)))
                ((px py) (actually (normal  1))))
     (values mx my px py)))

is not actually as tight as it could be:

 (define (two-sides actually)
 
   (define (normal direction)
     (actually (make-polar radius (+ a (* (/ PI 2) direction)))))
 
   (let-values (((mx my) (normal -1))
                ((px py) (normal  1)))
     (values mx my px py)))

but hey, that's a code enhancement opportunity to mull over while
posting, what luck!  The point is, the usual alternative to this
structuring would be to define a "graphics and board context, both
fundamental and elaborated" object to pass around.  Shudder.  I'd
rather have that monster out in the open and fixed (lexically),
than roaming hidden behind getters / setters and All That Rot (er,
entropy :-D).  (It helps, too, to live in Emacs, froth froth.)

OK, time to calm down.  Scheme is dangerously invigorating...

-- 
Thien-Thi Nguyen
GPG key: 4C807502

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