Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!mit-eddie!uw-beaver!tektronix!uunet!mcvax!diku!damm
From: damm@diku.dk (Kristian Damm Jensen)
Newsgroups: comp.lang.pascal
Subject: Multiple function-values (was: Re: The gaping hole left by var parameters ...)
Message-ID: <3854@diku.dk>
Date: 29 May 88 14:35:13 GMT
References: <5879@uwmcsd1.UUCP> <3499@omepd> <5915@uwmcsd1.UUCP>
Organization: DIKU, U of Copenhagen, DK
Lines: 65

In article <5915@uwmcsd1.UUCP> markh@csd4.milw.wisc.edu (Mark William Hopkins) writes:
>In article <3499@omepd> bobdi@omepd.UUCP (Bob Dietrich) writes:
     << stuf deleted >>
>You have a point on one matter: as long a Pascal does not allow files-as-values
>side-effects must occur be allowed in functions.  Also, as long as Pascal does 
>not allow the one to construct functions that can return MULTIPLE values, one
>will need to write procedures with var parameters in their stead.

This is not correct. A way to overcome this problem is to put those
multiple values in a record, and let the function return a pointer to
the record. Agreed, this doesn't seem very elegant, but it works, an you 
favor a LISP-like programming style, then it's very handy.

>Example:

>		 procedure Switch(var A, B : char);
>		 var C : char;
>		 begin
>		    C := A; A := B; B := C
>                 end;

>called in the environment 

>			 Switch (X, Y)

>would become:

>		function Switch(A, B : char) --> (char, char);
>		var C : char;
>		begin
>		   C := A; A := B; B := C;
>		   return (A, B)
>                end;

>called as follows:

>		      (X, Y) := Switch(X, Y)

This example would then become

	Type
	   TwoCharPointer = ^ThoCharRecord;
	   TwoCharRecord =
	      Record
	         a, b : Char
	      End;

	Function Switch (TwoChars : TwoCharRecord) : TwoCharPointer;
	   Var
	     help : Char;
	     Return : TwoCharPointer;
	Begin
	   With ThoChars Do
	      Begin
		 help := a;
		 a := b;
		 b := help
	      End;
	   Return^ := TwoChars;
	   Switch := Return
	End;


-- 
Kristian Damm Jensen (damm@diku.denet.uucp)