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In article <1992Oct6.195605.22657@email.tuwien.ac.at> ulrich@mips.complang.tuwien.ac.at writes:
>(*
>	Hello, I have some problems in understanding the WITH-statement
>	in Oberon-2 and would appreciate some help.
>
>	As far as I understood the Oberon-2 report, the procedure Subel1
>	below, should be equivalent to the procedure Subel2.
>	However, in Subel2 an error is reported by the compiler.
>	Even if a type guard is added (Subel3), the error remains.
>	(The procedures are a stripped down version of some more
>	useful code, indeed.)
>
>	The platform was DECoberon Release 2.6
>	(Oberon.2.6.tar.Z last modified Oct 3 21:09)
>	
>
>	Thanks in advance
>	Ulrich
>*)
>
>MODULE StatementWITH;
>TYPE
>	T0 = POINTER TO T0X;
>	T0X = RECORD END;
>
>	T1 = POINTER TO T1X;
>	T1X = RECORD(T0X) ARG: POINTER TO ARRAY OF T0 END;
>
>PROCEDURE Subel1(t0: T0);
>BEGIN
>	Subel1(t0(T1).ARG[0])
>END Subel1;
>
>PROCEDURE Subel2(t0: T0);
>BEGIN
>	WITH t0: T1 DO
>		Subel2(t0.ARG[0]) (* error 113 "incompatible assignment *)
>	END
>END Subel2;
>
>PROCEDURE Subel3(t0: T0);
>BEGIN
>	WITH t0: T1 DO
>		Subel3(t0(T1).ARG[0]) (* error 113 "incompatible assignment" *)
>	END
>END Subel3;
>END StatementWITH.
>

A version that compiles follows:

[types and Subel1 deleted]

PROCEDURE Subel2(t0: T0);
VAR
  t: T0;
BEGIN
        WITH t0: T1 DO
  	  t := t0.ARG[0];
        END;
        Subel2 (t)
END Subel2;

(* it looks like a front-end bug in Subel2 as there should be no difference
   between assignment to a variable and passing the designator as a param
   (at least in this case.)
*)

PROCEDURE Subel3(t0: T0);
BEGIN
        Subel3(t0(T1).ARG[0])
END Subel3;

(* The WITH statement is unnecessary with the guard. *)


I have written quite a bit of code using the WITH statement and haven't
encountered this bug. I suspect it's related to the use of the open array
rather than a general problem with WITH statements.


-- 
Cheryl Lins  Oberon Paladin  lins@apple.com