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From: warwick@cs.uq.oz.au (Warwick Allison)
Newsgroups: comp.lang.modula2
Subject: Re: POINTER/LINKED LIST HELP?
Message-ID: <523@uqcspe.cs.uq.oz.au>
Date: 2 Apr 91 02:00:21 GMT
References: <1991Mar30.151406.29367@kuhub.cc.ukans.edu> <5164@uniol.UUCP> <1991Apr1.123810.29390@kuhub.cc.ukans.edu>
Sender: news@cs.uq.oz.au
Reply-To: warwick@cs.uq.oz.au
Lines: 71

As a representative example, let me show you:

DEFINITION MODULE Lists;
FROM SYSTEM	IMPORT BYTE;

TYPE	List;
PROCEDURE EmptyList():List;
PROCEDURE Insert(VAR Into:List; Element:ARRAY OF BYTE);

END Lists.
-------------------
IMPLEMENTATION MODULE Lists;

FROM SYSTEM	IMPORT BYTE;
FROM Storage	IMPORT ALLOCATE;


TYPE	List=POINTER TO ListRec;
	ListRec =
		RECORD
			Data:ADDRESS;
			Size:CARDINAL;
			Next:List;
		END;

PROCEDURE EmptyList():List;
BEGIN
	RETURN NIL
END EmptyList;

PROCEDURE Insert(VAR Into:List; Element:ARRAY OF BYTE);

VAR	Head:List;
	Byte:CARDINAL;

BEGIN
	NEW(Head);
	WITH Head^ DO
		Size:=HIGH(Element)+1;
		ALLOCATE(Data,Size);
		FOR Byte:=0 TO HIGH(Element) DO
			Data[Byte]:=Element[Byte];
		END;
		Next:=Into;
	END;
	Into:=Head;
END Insert;

END Lists.

------------------------------
Okay, ignoring any syntax errors I have made, this works on most
Modula-2 compilers.  In particular, those supporting the ARRAY OF BYTE
standard.  This standard dictates that ANY type can be passed to a field
which is an ARRAY OF BYTE.

This is in no way a full complement of procedures, but it is
easy to implement the rest, once you see the basic technique.

now try...	Append, Delete, NthElement, Cardinality, IsIn, etc.

Oh, notice that these procedures are not VERY efficient, with all the
block data passing, but they work quite well, and are very generic.

Have fun,
Warwick.
--
  _--_|\   	warwick@cs.uq.oz.au
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 \_.--._/ 	University of Queensland,
       v    	AUSTRALIA.