| writing recursive functions [message #15645] |
Thu, 03 June 1999 00:00  |
Martin Downing
Messages: 136
Registered: September 1998
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Senior Member |
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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
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