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Date:	Fri, 8 Apr 2005 22:52:39 PDT7
From:	Peter Skye <pskye@peterskye.com >
Reply-To:	scoug-programming@scoug.com
To:	scoug-programming@scoug.com
Subject:	SCOUG-Programming: Rexx file rename ?

Content Type: text/plain

Hi Gary, thanks for looking in those two Rexx libraries.

> You didn't state why you desire a function in place of a command call, but if you really
> need such a function, it would be easy enough to write your own as a procedure call.

To me they're both the same -- function, procedure, even subroutine.
Subroutine is an old word I don't see any more; function and procedure
are exactly the same as far as I know (including at the assembler level)
with one exception: a function returns a value that the caller is to
use in an assignment or expression.

In other words, X = func(y) will set X, but X = proc(z) won't because
proc() doesn't return a value that the expression can use. Both
functions and procedures can do lots of other things such as calculate
*other* values too, but only the function returns a value in a way that
the caller can directly calculate with it. In Rexx a function does this
by returning a value, for example "return 255", rather than a procedure
which does only a "return".

Often a function that does something with a file system (such as Rename
A File) will return a result code to let you know if it was successful
or not. For example,

DataFile = "GaryCookieRecipes.txt"
NewNameFile = "CookieRecipiesStolenByTheDuck.txt"
rc = Rename( DataFile, NewNameFile )
if rc \= 0 then do
say "Oops, some kind of error: rc =" rc
if rc = 3 then say " (no such file)"
if rc = 8 then say " (file readonly attribute is set)"
if rc = 17 then say " (file is locked)"
if rc = 27 then say " (disk is locked)"
EXIT
end

Of course, you can write Rexx and ignore the returned value. Both of
the following are correct:

rc = Rename( DataFile, NewNameFile )
call Rename DataFile, NewNameFile

In the latter statement, if you want the return code you have to ask
Rexx to give you "the last return code that was created". I can't
remember the variable name that holds the value. I also don't know of
any other language that does this for you.

Anyway, you asked why I wanted a function rather than a procedure. It's
so I can look at the return code and see if the Rename was successful or
not. :-)

- Peter

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