Re: [fpc-pascal] Illegal counter variable?

[wkitty42]

On 9/11/19 1:06 AM, Ralf Quint wrote:

On 9/10/2019 4:26 PM, wkitt...@windstream.net wrote:

On 9/9/19 10:11 AM, James Richters wrote:

Pascal doesn't have things like step...


hunh??? i don't think that's right but i'm just catching up after several 10+ 
hours days of $job...


i know that i've written code in the past that did use something to step X 
numbers per run through the look and it did not involved manually incrementing 
the loop var...



I am not aware of any Pascal implementation that does have a STEP parameter for 
FOR loops, and I am programming in Pascal at least as long as you... ;-)


i may be thinking of a while loop... am in the middle of 10+ hour days at the 
moment... first since May of this year... at least now i don't have to go to the 
food bank for eats... maybe this weekend i can scan my old TP6 code and find 
what i'm remembering?? i dunno...


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Re: [fpc-pascal] Illegal counter variable?

[James Richters]

I reported it here:

https://bugs.freepascal.org/view.php?id=36065

 

James

 

>Actually, the original code used two VARs, not typed CONST. One VAR was 
>initialized and one was not. I think this is a bug and should be fixed.


>As Jonas already pointed out:

 

>"var i : longint = 0;" is internally handled using the same code path as 

>"const i : longint = 0", and typed constants cannot be used as counter 

>variables. This is indeed probably a bug.

 

> On Wed, 11 Sep 2019 12:40:57 -0400  > wrote 

 

>Yes, off topic. 

>The initial poster's code had the loop variable declared as an initialized 
>constant. Not as a true variable. No FPC in hand, I can't test if setting 
>'assignable typed >constants = true' would permit the use of an initialized 
>typed constant or not. 

 

 

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Re: [fpc-pascal] Illegal counter variable?

[DougC]

Actually, the original code used two VARs, not typed CONST. One VAR was 
initialized and one was not. I think this is a bug and should be fixed.


As Jonas already pointed out:

"var i : longint = 0;" is internally handled using the same code path as 

"const i : longint = 0", and typed constants cannot be used as counter 

variables. This is indeed probably a bug.




 On Wed, 11 Sep 2019 12:40:57 -0400   wrote 


Yes, off topic. The initial poster's code had the loop variable declared as an 
initialized constant. Not as a true variable. No FPC in hand, I can't test if 
setting 'assignable typed constants = true' would permit the use of an 
initialized typed constant or not. ___
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Re: [fpc-pascal] Illegal counter variable?

[scoxb...@shaw.ca]

Yes, off topic. The initial poster's code had the loop variable declared as an initialized constant. Not as a true variable. No FPC in hand, I can't test if setting 'assignable typed constants = true' would permit the use of an initialized typed constant or not. Sent from my Huawei phone Original Message --------Subject: Re: [fpc-pascal] Illegal counter variable?From: DougC To: FPC-Pascal users discussions CC: The last messages have wandered off topic somewhat. Can we stick to the original request, which was why the handling of the two declarations differed?Doug C.___
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Re: [fpc-pascal] Illegal counter variable?

[Sven Barth via fpc-pascal]

James Richters  schrieb am Mi., 11. Sep.
2019, 16:24:

> How do you get ‘By’ to work?   I have downto working but if I try ‘By’ I
> get
>
>
>
> Fatal: Syntax error, "DO" expected but "identifier BY" found
>

Did you see anywhere that said that this bug report was resolved and the
patch integrated into trunk?


>
> If FPC is going to support downto and by, why not also support changing
> the control variable when not in {$Mode TP} as well, and just make a note
> that doing so may not be compatible with other pascal compilers.. but who
> cares anyway FPC is better than all the others anyway 😊
>

There is no interest in lifting that restriction. Out of the dialects that
FPC supports TP is the only one that does not. Even Wirth advised against
allowing it.

Also FPC already supports downto. Just like TP and Delphi do...

Regards,
Sven

>
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Re: [fpc-pascal] Illegal counter variable?

[James Richters]

I don't know what the syntax would be if it did have a way to do a step

https://wiki.lazarus.freepascal.org/FOR..DO

"In Pascal, the for loop can only count in increments (steps) of 1"

James

-Original Message-
From: fpc-pascal  On Behalf Of 
wkitt...@windstream.net
Sent: Tuesday, September 10, 2019 7:26 PM
To: fpc-pascal@lists.freepascal.org
Subject: Re: [fpc-pascal] Illegal counter variable?

On 9/9/19 10:11 AM, James Richters wrote:
> Pascal doesn't have things like step...

hunh??? i don't think that's right but i'm just catching up after several 10+ 
hours days of $job...

i know that i've written code in the past that did use something to step X 
numbers per run through the look and it did not involved manually incrementing 
the loop var...


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Re: [fpc-pascal] Illegal counter variable?

[James Richters]

How do you get ‘By’ to work?   I have downto working but if I try ‘By’ I get

 

Fatal: Syntax error, "DO" expected but "identifier BY" found

 

If FPC is going to support downto and by, why not also support changing the 
control variable when not in {$Mode TP} as well, and just make a note that 
doing so may not be compatible with other pascal compilers.. but who cares 
anyway FPC is better than all the others anyway 😊 

 

>Well, we do have a patch for "for ... (down)to ... by" support: 
>https://bugs.freepascal.org/view.php?id=25549

 

James

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Re: [fpc-pascal] Illegal counter variable?

[Martin Wynne]

If step is wanted, it's easy enough:

For n:=a to b Do
   Begin
     if n Mod step <> 0 then Continue;
     ...



p.s. make that

  if (n-a) Mod step <> 0 then Continue;

for cases where a is not a multiple of step.

Martin.

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Re: [fpc-pascal] Illegal counter variable?

[Martin Wynne]

I am not aware of any Pascal implementation that does have a STEP 
parameter for FOR loops


If step is wanted, it's easy enough:

For n:=a to b Do
  Begin
if n Mod step <> 0 then Continue;
...


Martin.

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Re: [fpc-pascal] Illegal counter variable?

[Sven Barth via fpc-pascal]

Christo Crause  schrieb am Mi., 11. Sep. 2019,
09:54:

>
> On Wed, Sep 11, 2019 at 7:06 AM Ralf Quint  wrote:
>
>> On 9/10/2019 4:26 PM, wkitt...@windstream.net wrote:
>> > On 9/9/19 10:11 AM, James Richters wrote:
>> >> Pascal doesn't have things like step...
>> >
>> > hunh??? i don't think that's right but i'm just catching up after
>> > several 10+ hours days of $job...
>> >
>> > i know that i've written code in the past that did use something to
>> > step X numbers per run through the look and it did not involved
>> > manually incrementing the loop var...
>> >
>> >
>> I am not aware of any Pascal implementation that does have a STEP
>> parameter for FOR loops, and I am programming in Pascal at least as long
>> as you... ;-)
>>
>
> FPC documentation:
> https://www.freepascal.org/docs-html/ref/refsu58.html#x164-18600013.2.4 -
> at least FPC doesn't allow specifying an increment size.  Several other
> languages do allow specifying an increment (nice list of for loop
> constructs with specified increment in various languages:
> https://www.rosettacode.org/wiki/Loops/For_with_a_specified_step).  Modula-2
> or Oberon-2 code snippets could perhaps be mistaken for Pascal through the
> mists of time.
>

Well, we do have a patch for "for ... (down)to ... by" support:
https://bugs.freepascal.org/view.php?id=25549

Regards,
Sven

>
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Re: [fpc-pascal] Illegal counter variable?

[Christo Crause]

On Wed, Sep 11, 2019 at 7:06 AM Ralf Quint  wrote:

> On 9/10/2019 4:26 PM, wkitt...@windstream.net wrote:
> > On 9/9/19 10:11 AM, James Richters wrote:
> >> Pascal doesn't have things like step...
> >
> > hunh??? i don't think that's right but i'm just catching up after
> > several 10+ hours days of $job...
> >
> > i know that i've written code in the past that did use something to
> > step X numbers per run through the look and it did not involved
> > manually incrementing the loop var...
> >
> >
> I am not aware of any Pascal implementation that does have a STEP
> parameter for FOR loops, and I am programming in Pascal at least as long
> as you... ;-)
>

FPC documentation:
https://www.freepascal.org/docs-html/ref/refsu58.html#x164-18600013.2.4 -
at least FPC doesn't allow specifying an increment size.  Several other
languages do allow specifying an increment (nice list of for loop
constructs with specified increment in various languages:
https://www.rosettacode.org/wiki/Loops/For_with_a_specified_step).  Modula-2
or Oberon-2 code snippets could perhaps be mistaken for Pascal through the
mists of time.
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Re: [fpc-pascal] Illegal counter variable?

[Ralf Quint]

On 9/10/2019 4:26 PM, wkitt...@windstream.net wrote:

On 9/9/19 10:11 AM, James Richters wrote:

Pascal doesn't have things like step...


hunh??? i don't think that's right but i'm just catching up after 
several 10+ hours days of $job...


i know that i've written code in the past that did use something to 
step X numbers per run through the look and it did not involved 
manually incrementing the loop var...



I am not aware of any Pascal implementation that does have a STEP 
parameter for FOR loops, and I am programming in Pascal at least as long 
as you... ;-)


The closest would be the FOR..IN variant, which works in Delphi (D2006? 
and later) and is AFAIK supported in FPC by now. But that would be 
iterating over a set, not increment an integer/cardinal variable in an 
increment other than 1...


Ralf

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Re: [fpc-pascal] Illegal counter variable?

[wkitty42]

On 9/9/19 10:11 AM, James Richters wrote:

Pascal doesn't have things like step...


hunh??? i don't think that's right but i'm just catching up after several 10+ 
hours days of $job...


i know that i've written code in the past that did use something to step X 
numbers per run through the look and it did not involved manually incrementing 
the loop var...



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Re: [fpc-pascal] Illegal counter variable?

[James Richters]

I’m trying to use it in a way that always worked in Turbo Pascal for DOS, I 
have no idea how to program in C,  I find Pascal much more clear and easy to 
follow and C just confuses me, so I never spent much time other than a few 
stray projects here and there on C…  I’ve always used pascal since the 80s, and 
in fact my units that change the for loop variable that run in {$Mode TP} are 
the original code from turbo pascal written in the 80s.. over the decades I’ve 
modified stuff all around it, but the actual code with for loops with changing 
control variables is the exact same code I was running on old 4.7MHz Dos 
machines with turbo pascal for DOS…  so for nearly 40 years I have never even 
known there was some rule against changing the control variable in for loops,  
it’s always worked and I’ve always used it.. and it still works if I use {$Mode 
TP}  it may not work if I try to use Delphi or something else, and there may be 
some pascal version even older than turbo pascal for DOS that didn’t act this 
way, but from the entire scope of my programming experience, this is something 
that has just always worked and I never had a reason not to use it.

 

James

 

From: fpc-pascal  On Behalf Of Markus 
Greim
Sent: Monday, September 9, 2019 1:32 PM
To: FPC-Pascal users discussions 
Subject: Re: [fpc-pascal] Illegal counter variable?

 

James, 

 

not every body is using a GHz machine. I am , for example, programming a 80186 
in an embedded system with very limited speed an RAM. 

But I understand thats not a general argument. 

 

But look at MISRA C. Its a big set of rules for "real" save C programming, more 
or less now the standard in the automobile industry. 

Also here are strict rules for counters in for loops. 

See: 

https://www.misra.org.uk/forum/viewtopic.php?t=272​

 

So what they are doing is writing Pascal programs in C... ;-) And they need 
huge and expensive and complex  tools to check the C code for 

MISRA compatibility!

So we should NOT give up the safety of Pascal for the sloppiness of C! 

 

Kind Regards

 

Markus

  
<https://app.frontapp.com/api/1/noauth/companies/schleibinger_geraete_gmbh/seen/msg_3t3yn9e/han_9pzu6a/a2c200f4.gif>
 



On September 9, 2019, 7:19 PM GMT+2 ja...@productionautomation.net 
<mailto:ja...@productionautomation.net>  wrote:

Yes, today such limitations do seem too restrictive, I wonder if the reasons 
for the restrictions have become obsolete. You would have to have a really slow 
computer with very limited resources to optimize loops to the point of reducing 
functionality like this, and the tendency with modern pc's is to have a larger 
library of much more powerful and more flexible tools, even if they are more 
complex and take more memory and resources. For example Case statements used to 
only work with characters or integers, but the modern version now also works 
with strings, very much added functionality for sure, but also would use more 
resources but we would all rather have the capability because even a 
raspberry pi is blazing fast and has ram to burn compared to our old 8086s It 
seems silly to me that I can't so what I used to do with Turbo Pascal for DOS 
where I was limited to programs of a few hundred K, due to optimizations that 
just can't make much of a difference at all on modern computers. I am happy 
that FPC has TP compatibility mode though! It's just I get to a point where I 
eventually can't cross units since I can't have a circular unit reference. So I 
have to choose for any given unit.. do I want my old for loops and change the 
control variables, or do I want cool new case statements... etc.. it would be 
nice to have {$Mode everything_the_way_I_want_it}

Since the compiler knows I was trying to change the variable inside the for 
loop, could it not just compile in not quite as efficient code (TP MODE for 
loop) when it detects this, and use the more efficient optimized code when it 
detects that it is able to use it?

James

-Original Message-
From: fpc-pascal mailto:fpc-pascal-boun...@lists.freepascal.org> > On Behalf Of Bernd Oppolzer
Sent: Monday, September 9, 2019 10:46 AM
To: FPC-Pascal users discussions mailto:fpc-pascal@lists.freepascal.org> >
Subject: Re: [fpc-pascal] Illegal counter variable?

Am 09.09.2019 um 16:11 schrieb James Richters:


> I just don't see why having the limitation, there is no technical 
> reason that the for loop couldn't change that I can see.. especially since it 
> works in TP mode.

The original reason why some Pascal implementations had this limitation:

for performance or optimization reasons, the loop control variable was 
transferred to a register at the beginning of the loop, and changing the 
variable (at its storage location) inside the loop simply had no effect, 
because the variable was not fetched from there again during loop execution.
Worse: maybe, to make read accesses to

Re: [fpc-pascal] Illegal counter variable?

[Markus Greim]

James, 



not every body is using a GHz machine. I am , for example, programming a 80186 
in an embedded system with very limited speed an RAM. 

But I understand thats not a general argument. 



But look at MISRA C. Its a big set of rules for "real" save C programming, more 
or less now the standard in the automobile industry. 

Also here are strict rules for counters in for loops. 

See: 

https://www.misra.org.uk/forum/viewtopic.php?t=272​


So what they are doing is writing Pascal programs in C... ;-) And they need 
huge and expensive and complex tools to check the C code for 

MISRA compatibility!
So we should NOT give up the safety of Pascal for the sloppiness of C! 

Kind Regards


Markus

--- original message ---
On September 9, 2019, 7:19 PM GMT+2 ja...@productionautomation.net wrote:

Yes, today such limitations do seem too restrictive, I wonder if the reasons 
for the restrictions have become obsolete. You would have to have a really slow 
computer with very limited resources to optimize loops to the point of reducing 
functionality like this, and the tendency with modern pc's is to have a larger 
library of much more powerful and more flexible tools, even if they are more 
complex and take more memory and resources. For example Case statements used to 
only work with characters or integers, but the modern version now also works 
with strings, very much added functionality for sure, but also would use more 
resources but we would all rather have the capability because even a 
raspberry pi is blazing fast and has ram to burn compared to our old 8086s It 
seems silly to me that I can't so what I used to do with Turbo Pascal for DOS 
where I was limited to programs of a few hundred K, due to optimizations that 
just can't make much of a difference at all on modern computers. I am happy 
that FPC has TP compatibility mode though! It's just I get to a point where I 
eventually can't cross units since I can't have a circular unit reference. So I 
have to choose for any given unit.. do I want my old for loops and change the 
control variables, or do I want cool new case statements... etc.. it would be 
nice to have {$Mode everything_the_way_I_want_it}

Since the compiler knows I was trying to change the variable inside the for 
loop, could it not just compile in not quite as efficient code (TP MODE for 
loop) when it detects this, and use the more efficient optimized code when it 
detects that it is able to use it?

James

-Original Message-
From: fpc-pascal  On Behalf Of Bernd 
Oppolzer
Sent: Monday, September 9, 2019 10:46 AM
To: FPC-Pascal users discussions 
Subject: Re: [fpc-pascal] Illegal counter variable?

Am 09.09.2019 um 16:11 schrieb James Richters:

>> I just don't see why having the limitation, there is no technical 

>> reason that the for loop couldn't change that I can see.. especially since 
>> it works in TP mode.


> The original reason why some Pascal implementations had this limitation:


> for performance or optimization reasons, the loop control variable was 
> transferred to a register at the beginning of the loop, and changing the 
> variable (at its storage location) inside the loop simply had no effect, 
> because the variable was not fetched from there again during loop execution.

> Worse: maybe, to make read accesses to the loop control variable valid inside 
> the loop, they are prepared by storing the control register value into the 
> loop control variable, thus turning changes to the loop control variable 
> useless.


> Forbidding (write) accesses to the loop control variable allows for many 
> aggressive optimization strategies around loops.


> Maybe today such limitations seem too restrictive.


> Kind regards


> Bernd


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Re: [fpc-pascal] Illegal counter variable?

[Markus Greim]

AFAIK these is the standard behavior since the first PASCAL versions. 

We must not change it. It prevents a lot of side effects, and PASCAL is NOT C 
without brackets!
Use while or repeat instead!



>From Niklaus Wirths last 2004 Oberon manual: 

https://people.inf.ethz.ch/wirth/ProgInOberon2004.pdf​




t "It is recommended that the for statement be used in simple cases only; in 
particular, no 
components of the expressions determining the range must be affected by the 
repeated 
statements, and, above all, the control variable itself must not be changed by 
the repeated 
statements. The value of the control variable must be considered as undefined 
after the for 
statement is terminated."

Kind Regards


Markus

--- original message ---
On September 9, 2019, 5:20 PM GMT+2 mar...@templot.com wrote:

On 09/09/2019 15:11, James Richters wrote:

>> If (I>86) And (I<95) then Continue;

>> What does continue do exactly? Loop back to the beginning of the for loop 
>> right away?


> Hi James,


> Yes in effect -- it jumps forward to the test at the end of a loop. Very 

> useful.


> See: https://www.freepascal.org/docs-html/rtl/system/continue.html


> cheers,


> Martin.

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Re: [fpc-pascal] Illegal counter variable?

[James Richters]

Maybe there's no technical reason it doesn't work... it's just set to not work 
to make it compatible with other pascal programs?

-Original Message-
From: fpc-pascal  On Behalf Of Mattias 
Gaertner via fpc-pascal
Sent: Monday, September 9, 2019 1:32 PM
To: fpc-pascal@lists.freepascal.org
Cc: Mattias Gaertner 
Subject: Re: [fpc-pascal] Illegal counter variable?

On Mon, 9 Sep 2019 19:27:49 +0200
Bart  wrote:

> On Mon, Sep 9, 2019 at 4:54 PM Jonas Maebe 
> wrote:
> 
> > "var i : longint = 0;" is internally handled using the same code 
> > path as "const i : longint = 0", and typed constants cannot be used 
> > as counter variables. This is indeed probably a bug.
> 
> D7 does not allow this for global variables: "for loop variables must 
> be simple local variables".
> In D7 you cannot initialize a local variable, so I cannot test that 
> scenario. Someone with a more recent Delphi should check if this 
> sysnatx is allowed.

Same in 10.3.

Mattias
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Re: [fpc-pascal] Illegal counter variable?

[Mattias Gaertner via fpc-pascal]

On Mon, 9 Sep 2019 19:27:49 +0200
Bart  wrote:

> On Mon, Sep 9, 2019 at 4:54 PM Jonas Maebe 
> wrote:
> 
> > "var i : longint = 0;" is internally handled using the same code
> > path as "const i : longint = 0", and typed constants cannot be used
> > as counter variables. This is indeed probably a bug.  
> 
> D7 does not allow this for global variables: "for loop variables must
> be simple local variables".
> In D7 you cannot initialize a local variable, so I cannot test that
> scenario. Someone with a more recent Delphi should check if this
> sysnatx is allowed.

Same in 10.3.

Mattias
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Re: [fpc-pascal] Illegal counter variable?

[Bart]

On Mon, Sep 9, 2019 at 4:54 PM Jonas Maebe  wrote:

> "var i : longint = 0;" is internally handled using the same code path as
> "const i : longint = 0", and typed constants cannot be used as counter
> variables. This is indeed probably a bug.

D7 does not allow this for global variables: "for loop variables must
be simple local variables".
In D7 you cannot initialize a local variable, so I cannot test that scenario.
Someone with a more recent Delphi should check if this sysnatx is allowed.

-- 
Bart
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Re: [fpc-pascal] Illegal counter variable?

[James Richters]

Yes, today such limitations do seem too restrictive, I wonder if the reasons 
for the restrictions have become obsolete.  You would have to have a really 
slow computer with very limited resources to optimize loops to the point of 
reducing functionality like this, and the tendency with modern pc's is to have 
a larger library of much more powerful and more flexible tools, even if they 
are more complex and take more memory and resources.  For example Case 
statements used to only work with characters or integers,  but the modern 
version now also works with strings, very much added functionality for sure, 
but also would use more resources but we would all rather have the 
capability because even a raspberry pi is blazing fast and has ram to burn 
compared to our old 8086s  It seems silly to me that I can't so what I used to 
do with Turbo Pascal for DOS where I was limited to programs of a few hundred 
K, due to optimizations that just can't make much of a difference at all on 
modern computers.   I am happy that FPC has TP compatibility mode though!   
It's just I get to a point where I eventually can't cross units since I can't 
have a circular unit reference.  So I have to choose for any given unit.. do I 
want my old for loops and change the control variables, or do I want cool new 
case statements... etc..  it would be nice to have {$Mode 
everything_the_way_I_want_it}

Since the compiler knows I was trying to change the variable inside the for 
loop, could it not just compile in not quite as efficient code (TP MODE for 
loop) when it detects this, and use the more efficient optimized code when it 
detects that it is able to use it?

James

-Original Message-
From: fpc-pascal  On Behalf Of Bernd 
Oppolzer
Sent: Monday, September 9, 2019 10:46 AM
To: FPC-Pascal users discussions 
Subject: Re: [fpc-pascal] Illegal counter variable?


Am 09.09.2019 um 16:11 schrieb James Richters:
> I just don't see why having the limitation, there is no technical 
> reason that the for loop couldn't change that I can see.. especially since it 
> works in TP mode.


The original reason why some Pascal implementations had this limitation:

for performance or optimization reasons, the loop control variable was 
transferred to a register at the beginning of the loop, and changing the 
variable (at its storage location) inside the loop simply had no effect, 
because the variable was not fetched from there again during loop execution.
Worse: maybe, to make read accesses to the loop control variable valid inside 
the loop, they are prepared by storing the control register value into the loop 
control variable, thus turning changes to the loop control variable useless.

Forbidding (write) accesses to the loop control variable allows for many 
aggressive optimization strategies around loops.

Maybe today such limitations seem too restrictive.

Kind regards

Bernd

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Re: [fpc-pascal] Illegal counter variable?

[Martin Wynne]

On 09/09/2019 15:11, James Richters wrote:

If (I>86) And (I<95) then Continue;
What does continue do exactly?  Loop back to the beginning of the for loop 
right away?


Hi James,

Yes in effect -- it jumps forward to the test at the end of a loop. Very 
useful.


See: https://www.freepascal.org/docs-html/rtl/system/continue.html

cheers,

Martin.
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Re: [fpc-pascal] Illegal counter variable?

[Jonas Maebe]

On 2019-09-09 11:30, James Richters wrote:

Can someone please tell me why this happens?

Var
   I : Longint = 0;
Begin
For I := 1 to 6 Do
   Writeln(I);
End.

This gives me :
initialize.pas(4,5) Error: Illegal counter variable
initialize.pas(6,4) Fatal: There were 1 errors compiling module, 
stopping

initialize.pas(0) Fatal: Compilation aborted


"var i : longint = 0;" is internally handled using the same code path as 
"const i : longint = 0", and typed constants cannot be used as counter 
variables. This is indeed probably a bug.



Jonas
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Re: [fpc-pascal] Illegal counter variable?

[Bernd Oppolzer]

Am 09.09.2019 um 16:11 schrieb James Richters:

I just don't see why having the limitation, there is no technical reason that
the for loop couldn't change that I can see.. especially since it works in TP 
mode.



The original reason why some Pascal implementations had this limitation:

for performance or optimization reasons, the loop control variable was
transferred to a register at the beginning of the loop, and changing the
variable (at its storage location) inside the loop simply had no effect,
because the variable was not fetched from there again during loop 
execution.

Worse: maybe, to make read accesses to the loop control variable valid
inside the loop, they are prepared by storing the control register value
into the loop control variable, thus turning changes to the loop control
variable useless.

Forbidding (write) accesses to the loop control variable allows for many
aggressive optimization strategies around loops.

Maybe today such limitations seem too restrictive.

Kind regards

Bernd

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Re: [fpc-pascal] Illegal counter variable?

[James Richters]

If (I>86) And (I<95) then Continue; 
What does continue do exactly?  Loop back to the beginning of the for loop 
right away?   I didn't even know there was such a command.. it's not mentioned 
here:
https://wiki.lazarus.freepascal.org/FOR..DO

only break is mentioned.

As I said, there are ways around it, and that was just a stupid example that 
proves it works in {$Mode TP}  I have some really complicated nested for loops 
and changing the loop variable is really useful.. also it allows you to skip 
cycling around in the loop.  I just don't see why having the limitation, there 
is no technical reason that the for loop couldn't change that I can see.. 
especially since it works in TP mode.   Yes, I can work around it.. change to a 
while loop instead where or something.. where you can change variables all you 
want... I just don't see the point of enforcing this 
no-changing-the-for-loop-variable rule... 

Pascal doesn't have things like step... but if I modify the for variable myself 
I can make it act like it had step

{$Mode TP}
Var
   I:Byte;
Begin
  For I := 0 to 100 do
Begin
   Write(I,' ');
   Inc(I,3);
End;
End.
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 88 92 96 100

Or 

{$Mode TP}
Var
   I:Byte;
Begin
  For I := 101 downto 0 do
Begin
   Dec(I);
   Write(I,' ');
End;
End.
100 98 96 94 92 90 88 86 84 82 80 78 76 74 72 70 68 66 64 62 60 58 56 54 52 50 
48 46 44 42 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0

Yes lots of ways to do these things... but could always do it with for loops 
with Pascal before.. and they work fine this way in FPC if you are in TP mode, 
so why not just allow it all the time?... just to have the flexibility to do 
what you want.It would just be nice to get everything to work in all my 
units all the time.. but if I use TP mode, then I can't do things like use case 
statements with strings.

James

-Original Message-
From: fpc-pascal  On Behalf Of Martin 
Wynne
Sent: Monday, September 9, 2019 8:53 AM
To: fpc-pascal@lists.freepascal.org
Subject: Re: [fpc-pascal] Illegal counter variable?

On 09/09/2019 13:38, James Richters wrote:
> Var
> I:Byte;
> Begin
>I:=57;
>For I := I to 100 do
>  Begin
> If I=87 then
>I:=95;
> Write(I,' ');
>  End;
> End.

Why not:

Var
 I:Byte;
Begin
I:=57;
For I := I to 100 do
  Begin
 If (I>86) And (I<95) then Continue;
 Write(I,' ');
  End;
End.

which is much easier to follow the logic.

cheers,

Martin.
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Re: [fpc-pascal] Illegal counter variable?

[DougC]

The last messages have wandered off topic somewhat. 



Can we stick to the original request, which was why the handling of the two 
declarations differed?


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Re: [fpc-pascal] Illegal counter variable?

[Martin Wynne]

On 09/09/2019 13:38, James Richters wrote:

Var
I:Byte;
Begin
   I:=57;
   For I := I to 100 do
 Begin
If I=87 then
   I:=95;
Write(I,' ');
 End;
End.


Why not:

Var
I:Byte;
Begin
   I:=57;
   For I := I to 100 do
 Begin
If (I>86) And (I<95) then Continue;
Write(I,' ');
 End;
End.

which is much easier to follow the logic.

cheers,

Martin.
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Re: [fpc-pascal] Illegal counter variable?

[James Richters]

>That page only talks about assigning the loop var *inside* the loop, which is 
>forbidden.

You can re-assign the loop variable if you are in {$Mode TP} it works perfectly 
fine to re-assign the for variable inside the loop, and I use that extensively, 
I have TP units specifically so I can do that.  I really don't understand why 
it's forbidden if you aren't in TP mode...  programmers can take care of their 
own variables and don't need to be protected from themselves.  I have good 
reasons to want to change the for loop variable and never have a problem with 
it.  I know there are ways around it, but I prefer to just modify the for 
variable... it can be very powerful.

This works great! 

{$MODE TP}
Var
   I:Byte;
Begin
  I:=57;
  For I := I to 100 do
Begin
   If I=87 then
  I:=95;
   Write(I,' ');
End;
End.

Output:
57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 
83 84 85 86 95 96 97 98 99 100

James
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Re: [fpc-pascal] Illegal counter variable?

[James Richters]

I don't understand what difference it makes if I assign I :=0 with the variable 
declaration or If I was using I for something else..  It's irrelevant what the 
condition of I was before the for loop, just as it's irrelevant that the status 
of a variable is before you assign it to something.I just don't think this 
should produce any kind of an error,  I'm not doing anything technically wrong 
as far as I can tell.
I should be able to use I for a whole pile of things then re-cycle it in my for 
loop.. then use it for more stuff after.. the condition of I before or after 
the for loop is irrelevant, as long as I make sure I initialize it before using 
it.. everything should be fine.   I should be able to do this if I want:

Var
   I : Longint = 57;
Begin
Inc(I);
Writeln(I);
I:=50;
Inc(I);
Writeln(I);
For I := 1 to 6 Do
  Writeln(I);
I:=-10;
Inc(I);
Writeln(I);
End.

It should not matter what I was using I for before or after the for loop or if 
it was initialized or used for some other purpose before or after the loop.

James
-Original Message-
From: fpc-pascal  On Behalf Of Mattias 
Gaertner via fpc-pascal
Sent: Monday, September 9, 2019 5:59 AM
To: fpc-pascal@lists.freepascal.org
Cc: Mattias Gaertner 
Subject: Re: [fpc-pascal] Illegal counter variable?

On Mon, 9 Sep 2019 11:44:05 +0200
SPRL AFOR  wrote:

> Hi.
> 
> Index variable can neither be initialized nor computed. Read 
> https://wiki.lazarus.freepascal.org/FOR..DO

That page only talks about assigning the loop var *inside* the loop, which is 
forbidden.

James question is about the difference between an initialized global var and a 
non initialized global var.

My guess is that it has to do with the different exe/linker sections where 
these vars are put. Hopefully some compiler guru can explain.

Mattias

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Re: [fpc-pascal] Illegal counter variable?

[Mattias Gaertner via fpc-pascal]

On Mon, 9 Sep 2019 11:44:05 +0200
SPRL AFOR  wrote:

> Hi.
> 
> Index variable can neither be initialized nor computed. Read 
> https://wiki.lazarus.freepascal.org/FOR..DO

That page only talks about assigning the loop var *inside* the loop,
which is forbidden.

James question is about the difference between an initialized global
var and a non initialized global var.

My guess is that it has to do with the different exe/linker sections
where these vars are put. Hopefully some compiler guru can explain.

Mattias

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Re: [fpc-pascal] Illegal counter variable?

[SPRL AFOR]

Hi.

Index variable can neither be initialized nor computed. Read 
https://wiki.lazarus.freepascal.org/FOR..DO


Antonio

Le 09/09/2019 à 11:30, James Richters a écrit :

Can someone please tell me why this happens?

Var
I : Longint = 0;
Begin
For I := 1 to 6 Do
Writeln(I);
End.

This gives me :
initialize.pas(4,5) Error: Illegal counter variable
initialize.pas(6,4) Fatal: There were 1 errors compiling module, stopping
initialize.pas(0) Fatal: Compilation aborted

but this works fine:
Var
I : Longint;
Begin
I := 0;
For I := 1 to 6 Do
Writeln(I);
End.

Shouldn't these two programs be identical?  What difference does it make if I 
initialize the variable in the Var section?

James
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