[Oberon] Oberon System 3 on WIndows: Why does the step sizein FOR-loop have to be a constant expression?

[Skulski, Wojciech]

Joerg:

oh, I see. On reading the message I thought that the step was removed. I agree that the most common pattern is a constant step.

Wojtek
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From: Oberon [oberon-bounces at lists.inf.ethz.ch] on behalf of Jörg Straube [joerg.straube at iaeth.ch]
Sent: Sunday, December 9, 2018 7:27 PM
To: ETH Oberon and related systems
Subject: Re: [Oberon] Oberon System 3 on WIndows: Why does the step     sizein  FOR-loop have to be a constant expression?

Wojtek

«BY» is still in the language. It does not have to be 1. You can increment by 2, 3, 4, 12, 59 whatever, but it has to be constant. If it is a variable take WHILE.

Jörg

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Von: Skulski, Wojciech<mailto:skulski at pas.rochester.edu>
Gesendet: Montag, 10. Dezember 2018 01:24
An: ETH Oberon and related systems<mailto:oberon at lists.inf.ethz.ch>
Betreff: Re: [Oberon] Oberon System 3 on WIndows: Why does the step sizein FOR-loop have to be a constant expression?

Joerg:

Removing an increment "BY" from a FOR loop looks like a highly questionable optimization to me. I am not sure if the person who made this optimization wrote a lot of data processing code, or any at all. Stepping by an increment other than "1" is a common practice in data processing.

Wojtek
________________________________________
From: Oberon [oberon-bounces at lists.inf.ethz.ch] on behalf of Jörg Straube [joerg.straube at iaeth.ch]
Sent: Sunday, December 9, 2018 4:15 PM
To: ETH Oberon and related systems
Subject: Re: [Oberon] Oberon System 3 on WIndows: Why does the step size in     FOR-loop have to be a constant expression?

Use WHILE if step size is variable.

Jörg

> Am 09.12.2018 um 17:54 schrieb Dieter <d.gloetzel at web.de>:
>
> On page 273 of "Programming in Oberon" Wirth and Reiser write:
>
> FORStatement = "FOR" ident ":=" expression "TO" expression
>                              ["BY" ConstExpression "DO"]
>                               StatementSequence
>                              "END"
> And indeed when I try to put a variable as step size, the compiler doesn't like it.
>
> This means I cannot write reusable code, which allows to be executed under different conditions with different step sizes.
>
> I am sure, there is some reasoning behind this, but I find it kind-off inconvenient.
>
> Regards, Dieter
>
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