Re: Question: Tokenizing CDATA attribute values

[David Megginson <dmeggins@xxxxxxxxxx>]

W. Eliot Kimber writes:

 > While we're on the subject, can someone provide (or point me to) a
 > brief tutorial on the distinction between a simple define, "let"
 > procedures, and "lambda" procedures?  I seem to be being
 > particularly dim about these--probably too many years of procedural
 > programming to see the obvious in a scheme context.

The tricky part is that I was using named let (ISO/IEC 10179:1996,
clause 8.3.2.6).  When I do

  (let X ((a 10)
          (b 20))
    ...
  )

I'm not only creating new bindings for the variables "a" and "b", but
I'm binding X to a new function that takes "a" and "b" as arguments,
so that I can call (X ...) recursively to start a new iteration of the
loop (remember that tail-recursion is better than iteration in
Scheme).  In other words, the best equivalent for

  for (x = 0; x < 100; x++) {
    foo(x);
  }

in Scheme is

  (let loop-function ((x 0))
    (cond ((< x 100)
           (foo x)
           (loop-function (+ x 1)))))

It looks a little clumsy for straight-forward iteration, but it's very
nice for working through lists, etc.


All the best,


David

-- 
David Megginson                 ak117@xxxxxxxxxxxxxxxxxxx
Microstar Software Ltd.         dmeggins@xxxxxxxxxxxxx
University of Ottawa            dmeggins@xxxxxxxxxx
        http://www.uottawa.ca/~dmeggins

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