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From: mhx@iae.nl (Marcel Hendrix)
Subject: Re: FORTH Trouble--Please Show Me
Newsgroups: comp.lang.forth
Message-ID: <87851214938435@frunobulax.edu>
Date: Sun, 21 Oct 2012 23:50:48 +0200
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Paul Rubin <no.email@nospam.invalid> writes Re: FORTH Trouble--Please Show Me
[..]
> Example in Python:
>
>    def square(x):
>      return x*x
>
>    def derivative(f, h):  # approximate numerical derivative
>      def df(x):
>        return (f(x+h) - f(x)) / h
>      return df
>
>    print square(3)  # prints 9
>    print derivative(square,0.0001)(3)   # prints approximately 6

> You could write something like "derivative" in C with function pointers,
> but it would be much messier.
[..]

I doubt the much in "much messier."

-marcel

-- -------------------
ANEW -derivative

: eval ( ? xt -- ? ) ( F: ? -- ? ) EXECUTE ;

: derivative ( xt -- ) ( F: x h -- d )
  LOCAL f   FLOCALS| h x |
  x h F+ f eval   x f eval  F-  h F/ ;

CR 3e FSQR  F.                  \ prints 9
CR ' FSQR 3e 1e-4 derivative F. \ prints approximately 6

\ FORTH> in idata/derivative
\ 9.000000
\ 6.000100  ok