[Oberon] Module aliases - what is the correct way to handle them

[Chris Burrows]

I use the code as shown in ORB0.Mod in all versions of the Astrobe Oberon compiler for ARM Cortex M3, M4, M7 and Embedded Project Oberon for RISC5,

Regards,
Chris

Chris Burrows
CFB Software
https://www.astrobe.com



> -----Original Message-----
> From: Oberon [mailto:oberon-bounces at lists.inf.ethz.ch] On Behalf Of
> Andreas Pirklbauer
> Sent: Sunday, 9 February 2020 10:17 PM
> To: Oberon List
> Cc: Andreas Pirklbauer
> Subject: [Oberon] Module aliases - what is the correct way to handle
> them
> 
> The current implementation on projectoberon.com does not handle
> aliases correctly in all cases (see appendix below for an example).
> 
> Hence an implementation that DOES handle aliases in a correct way is
> required. However, this is tricky. One complication arises due to re-
> export and re-import of types across potentially many modules.
> Imports can be hidden, and a module can be simultaneously imported
> indirectly (hidden import) and directly.
> 
> Any input on the options shown below for ORB.ThisModule?
> 
> - ORB0 and ORB1 correctly detect an "invalid import order
> - ORB1 and ORB2 don t detect an "invalid import order
> 
> (see http://github.com/andreaspirklbauer/Oberon-test-module-aliases)
> 
> Feel free to add other possible ways to handle this correctly.
> 
> -ap
> 
>            ORB.ThisMod
> 
> **ORB0.Mod** (tests obj.name agains name and obj.orgname against
> obj.orgname separately)
> 
>     obj1 := topScope; obj := obj1.next;  (*search for module*)
>     WHILE (obj # NIL) & (obj.name # name) DO obj1 := obj; obj :=
> obj1.next END ;
>     IF obj = NIL THEN
>       obj1 := topScope; obj := obj1.next;
>       WHILE (obj # NIL) & (obj IS Module) & (obj(Module).orgname #
> orgname) DO
>         obj1 := obj; obj := obj1.next
>       END
>     END ;
> 
> **ORB1.Mod** (tests obj.name against name and obj.orgname against
> obj.orgname in a single loop)
> 
> This is similar to ORB0, but now there is a *type test* and a *type
> guard* for *every* import being checked.
> 
>     obj1 := topScope; obj := obj1.next;  (*search for module*)
>     WHILE (obj # NIL) & (obj IS Module) & (obj.name # name) &
> (obj(Module).orgname # orgname) DO
>       obj1 := obj; obj := obj1.next
>     END ;
> 
> **ORB2.Mod**  (tests only obj.orgname against orgname)
> 
>     obj1 := topScope; obj := obj1.next;  (*search for module*)
>     WHILE (obj # NIL) & (obj IS Module) & (obj(Module).orgname #
> orgname) DO
>       obj1 := obj; obj := obj1.next
>     END ;
> 
> **ORB3.Mod**  (tests obj.orgname agains name)
> 
>     obj1 := topScope; obj := obj1.next;  (*search for module*)
>     WHILE (obj # NIL) & (obj IS Module) & (obj(Module).orgname #
> name) DO
>       obj1 := obj; obj := obj1.next
>     END ;
> 
>            M.Mod
> 
> MODULE N0;
>   TYPE T0* = RECORD i: INTEGER END ;
> END N0.
> 
> MODULE N1;
>   TYPE T1* = RECORD i: INTEGER END ;
> END N1.
> 
> MODULE N2;
>   TYPE T1* = RECORD i: INTEGER END ;
> END N2.
> 
> MODULE M0;
>   TYPE T0* = RECORD i: INTEGER END ;
> END M0.
> 
> MODULE M1;
>   IMPORT M0;
>   TYPE T1* = RECORD (M0.T0) j: INTEGER END ; END M1.
> 
> MODULE M2;
>   IMPORT M1;
>   TYPE T2* = RECORD (M1.T1) k: INTEGER END ; END M2.
> 
> MODULE M3;
>   IMPORT N0 := M0, M2, N0;
>   TYPE T3* = RECORD (M2.T2) k: INTEGER END ; END M3.
> 
> ORP.Compile @/s ~
> 
> -----------------------------------------------------------
> 
> Try the above sequence with 4 different version of ORB:
> 
> ORP.Compile ORB0.Mod/s ~      # correct
> System.Free ORP ORG ORB ~
> Now recompile M3
> -> catches the "invalid import order" error
> 
> 
> ORP.Compile ORB1.Mod/s ~      # correct
> System.Free ORP ORG ORB ~
> Now recompile M3
> -> catches the "invalid import order" error
> 
> 
> ORP.Compile ORB2.Mod/s ~      # incorrect
> System.Free ORP ORG ORB ~
> Now recompile M3
> -> does NOT catch the "invalid import order" error
> 
> ORP.Compile ORB3.Mod/s ~      # incorrect
> System.Free ORP ORG ORB ~
> Now recompile M3
> -> does NOT catch the "invalid import order  error
> 
> 
> 
>      APPENDIX
> 
> The current implementation of module ORB does not compile the
> following 4 modules correctly.
> 
> MODULE M1; TYPE P1* = POINTER TO T1; T1* = RECORD x*: INTEGER END;
> END M1.
> MODULE M2; IMPORT M1; TYPE P2* = POINTER TO T2; T2* = RECORD(M1.T1)
> y*: INTEGER END; END M2.
> MODULE M3; IMPORT M1, M2; VAR x1: M1.P1; x2: M2.P2; BEGIN x1 := x2;
> END M3.
> MODULE M4; IMPORT Y1 := M1, Y2 := M2; VAR x1: Y1.P1; x2: Y2.P2; BEGIN
> x1 := x2; END M4.
> 
> Modules M1 to M3 compile, but M4 (which should do the same as M3)
> does not.
> 
> This was reported on:
> 
> http://github.com/schierlm/Oberon2013Modifications/tree/master/BugFix
> es
> 
> 
> 
> 
> 
> 
> 
> 
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