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From: luscher@nicmad.UUCP
Newsgroups: net.lang.forth
Subject: Re: Recursion forth
Message-ID: <680@nicmad.UUCP>
Date: Sun, 4-May-86 16:00:54 EDT
Article-I.D.: nicmad.680
Posted: Sun May  4 16:00:54 1986
Date-Received: Tue, 6-May-86 06:50:31 EDT
References: <1854@mtgzz.UUCP>
Reply-To: luscher@nicmad.UUCP (Jim {4thNIC} Luscher)
Organization: Nicolet Instrument Corp. Madison WI
Lines: 40

In article <1854@mtgzz.UUCP> bds@mtgzz.UUCP (b.d.szablak) writes:
>
>	I would appreciate it if someone well versed in forth programming
>could give this novice hints on coding recursive algorthims (the two Forth
>texts I have manage to avoid this topic). It seems the very first word that
>I (in all innocence) attempted to define was to evaluate the fibinocci
>function (in C):
>
>	fib(n)
>	{
>		if( n==1 || n==2 ) return 1;
>		return fib(n-1) + fib(n-2);
>	}
>

I recognize the Fibbonacci series here but I don't remember any deffinition
that gave a single number for it!  Anyway here is the FORTH code:

: fib ( n ) DUP 3 < IF  DROP 1  ( return 1 for 1 or 2, assumes n>=1  )
                    ELSE  [ SMUDGE ]  ( allow for recursion )
                        DUP 1- fib    ( here is your fib{n-1}  )
                        SWAP 2- fib   ( followed by  fib{n-2}  )
                        +  [ SMUDGE ] ( sum two fib s, end recursability )
                    THEN  ;

For arguments of n=  1   2   3   4   5   6   7   8
this gives results=  1   1   2   3   5   8  12  21

I don't know if this is quite what you wanted, but the RECURSION works fine!

Best wishes in exploring FORTH!


-- 

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