[Tutor] Re: parsing--is this right?

[Derrick 'dman' Hudson]

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On Tue, Jun 11, 2002 at 02:55:47PM -0400, Paul Tremblay wrote:
=20
| One of the confusing things for me is that in your code, a
| function calls itself.

This is a programming style/technique known as recursion.  Recursion
is really effective when the problem can be defined in terms of
itself.  Parsing nested structures (the {} in your RTF) is well suited
for recursion (and hence the name 'recursive descent' parser).

Another example of recursion is the factorial operation.

n! =3D  n * n-1 * n-2 * ... * 2 * 1

The "..." can be shown with recursion :

def fact( n ) :
    if n =3D=3D 1 :
        return 1
    else:
        return n * fact( n-1 )

Of course, for factorial, a faster implementation can be devised, but
the most natural definition of it is recursive.

(don't try this fact() on anything other than an integer >=3D 1
otherwise you'll get some bad results :-))

-D

--=20

"...the word HACK is used as a verb to indicate a massive amount
of nerd-like effort."  -Harley Hahn, A Student's Guide to Unix
=20
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