[Oberon] IMPORT Modules: why does order matter?

Michael Schierl schierlm at gmx.de
Sun Mar 3 14:22:41 CET 2019

Hello Jörg,

Am 03.03.2019 um 14:02 schrieb Jörg:

> Automatic replacement of EXIT is something along these rules:
> * LOOP statSeq END                            —> done := FALSE; REPEAT statSeq UNTIL done;
> * IF cond THEN statSeq; EXIT END;   —> IF cond THEN statSeq; done := TRUE
>   statSeq2                                                      ELSE statSeq2
>                                                                        END

This does not take into account EXIT statements that are nested deeper
(in IF, CASE, WITH, or probably (not sure if allowed in OBERON-2) nested
FOR loops).

My approach (which causes ugly code) would be:

Rewrite »LOOP statSeq END« to
»done := FALSE; REPEAT statSeq' UNTIL done;«

while statSeq' is derived from statSeq by

- wrapping every individual statement in
  »IF NOT done THEN statement END«
- if the statement is a block statement, derive its nested statement
  sequences by the same way
- rewrite nested FOR loops (if allowed) to terminate if done is true
- replace every EXIT by done := TRUE;

Other EXIT which are found and not eliminated by these rules are either
a bug in the rewriting algorithm implementation or a compile error in
the original source code.

In case every EXIT statement is only contained in an IF statement that
is a direct child of the LOOP, Jörg simpler's algorithm could be used as



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