| Re: writing recursive functions [message #15646 is a reply to message #15645] |
Wed, 02 June 1999 00:00   |
William Daffer
Messages: 34
Registered: February 1999
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Member |
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"Martin Downing" <m.downing@abdn.ac.uk> writes:
Are you using PVWave? fact.pro (take 1) worked fine in IDL 5.1.1.
William
> Hi all,
>
> My aim is to write a function that (recursively) call itself, that can be
> compiled on the fly as with standard code.
> So - whats the problem, well if you _could_ write a function for factorials
> using recursion as:
>
> ------------------------------------------------------------
> ; fact.pro : take 1
> ; example of recursion (I know there's a factorial function!!)
> function fact , n=n
> res = float(n)
> if res gt 1 then $
> res = res * fact(n=res-1)
> return, res
> end
> ; (I used a keyword as otherwise it compiles thinking fact() is a variable)
> ------------------------------------------------------------
>
> ....This will not compile
> It appears that the compiler needs something equivalent to a declaration
> statement (as in C code), so I tried to just write a dummy empty function
> above the real code.
>
> e.g.:
>
> ------------------------------------------------------------
> ;fact.pro : take2
> ; dummy definition I.e. declaration
> function fact , n
> print, "this should not be called!"
> return, n
> end
>
> ; the real code
> ; example of recursion (I know there's a factorial function!!)
> function fact , n
> res = float(n)
> if res gt 1 then $
> res = res * fact(res-1)
> return, res
> end
> ----------------------------------------------------------
> However, unless this is forcibly compiled (.compile fact.pro), the
> auto-compile will stop after the initial definition.
>
> This leaves two options - permanently compiling the code or calling by
> another routine:
>
> ------------------------------------------------------------
> ; call_fact.pro
> @fact.pro
> function call_fact, n
> return, fact(n)
> end
> ------------------------------------------------------------
>
>
> Any suggestions welcome
>
> Martin,
> Aberdeen, Scotland
>
>
>
>
>
>
>
--
Outside of a dog, a book is man's best friend
Inside of a dog, it's too dark to read.
Groucho Marx.
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