[Oberon] Tidyness of iteration.

[Alexander Ilin]

14.11.2016, 21:18, "peter at easthope.ca" <peter at easthope.ca>:
> (* Pre-2013. *)
> PROCEDURE LOOPiteration();
> BEGIN
>         Texts.OpenReader(R, t, 0);
>         LOOP
>                 Texts.Read(R, ch);
>                 IF R.eot THEN EXIT ELSE (* Process ch *) END
>         END
> END LOOPinteration.
>
> Project Oberon 2013, Page 5.
> "2. The LOOP and EXIT statements (repetitions with multiple exit points) have been discarded."
>
> (* Using REPEAT, R.eot must be checked twice in each iteration. *)
> PROCEDURE REPEATiteration();
> BEGIN
>         Texts.OpenReader(R, t, 0);
>         REPEAT
>                 IF ~R.eot THEN Texts.Read(R, ch); (* Process ch *) END
>         UNTIL R.eot
> END REPEATinteration.
>
> (* Using WHILE, Texts.Read is duplicated. *)
> PROCEDURE WHILEiteration();
> BEGIN
>         Texts.OpenReader(R, t, 0);
>         Texts.Read(R, ch);
>         WHILE ~R.eot
>                 (* Process ch *);
>                 Texts.Read(R, ch)
>         END
> END WHILEinteration.
>
> Can the REPEAT example or the WHILE example be simplified further?
> (One must wonder about discarding REPEAT and WHILE and retaining LOOP with
> strictly one EXIT.)

  The REPEATiteration should be as follows:

PROCEDURE REPEATiteration();
BEGIN
        Texts.OpenReader(R, t, 0);
        REPEAT
                Texts.Read(R, ch);
                IF ~R.eot THEN (* Process ch *) END
        UNTIL R.eot
END REPEATiteration;

  To simplify the code, why not return R.eot from the Texts.Read?

PROCEDURE WHILEiteration();
BEGIN
        Texts.OpenReader(R, t, 0);
        WHILE Texts.Read(R, ch)
                (* Process ch *)
        END
END WHILEiteration;

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 Александр