date:20171226

Re: [fpc-devel] * GMX Spamverdacht * An extension of fpc language: the BASED construct

2017-12-26 Thread Giuliano Colla




Il 26/12/2017 18:43, Karoly Balogh (Charlie/SGR) ha scritto:

As far as I understand (I did not try) this was once supported, but
explicitly removed by FPC 2.4.0 from Absolute keyword dereferencing is no
longer allowed:

http://wiki.freepascal.org/User_Changes_2.4.0#Absolute_variable_declarations

As the reasoning there shows, it's a very slippery slope this, which could
open a can of worms, so careful people.:)


What was allowed before 2.4.0 was *implicit* keyword dereferencing, 
while explicit dereferencing has never been allowed. This was rather 
inconsistent, and rightfully suppressed.


Giuliano

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Re: [fpc-devel] An extension of fpc language: the BASED construct

2017-12-26 Thread Giuliano Colla


Il 26/12/2017 18:26, Sven Barth via fpc-devel ha scritto:

Am 26.12.2017 13:33 schrieb "Giuliano Colla" 
>:


If the idea is not rejected, then a number of refinements (which
I'm ready to implement) are required to make the feature generally
available:


My following remarks are independent of an eventual acceptance of the 
feature :


- All architectures should be supported (now it's only for x86_64
- symcpu.pas).

It might be possible to implement this in a platform independent way 
that might simply need to expand the capabilites of "absolute".


The feature in itself is platform independent.

The only catch is that in pdecvar.pas (where variable declaration is 
handled) there's a per platform hook for each symbol type, in order to 
allow for special handling of some features.
For consistency I did follow the same rule, which is used for all the 
other declarations, disregarding whether they're platform independent or 
not.
As a consequence, for each supported platform you must add in its 
specific symcpu.pas a type entry:


tcpubasedvarsym = class(tbasedvarsym)
end;
tcpubasedvarsymclass = class of tcpubasedvarsym;

and a line of code:

  cbasedvarsym:=tcpubasedvarsym;

As this is tedious, I've only done it for the platform I'm using 
(x86_64/symcpu.pas). To deploy the feature, the same lines must be added 
in each platform symcpu.pas unit. There's no more that that.



- It should be decided if to make the feature generally available,
or conditioned by an {$IFDEF FPCHASBASED}

- It should be decided if the feature should be available in all
modes or only in a selected number of modes (what of TurboPascal
Mode or Delphi Mode?).

Rule of thumb: new features added as a separate mode switch, no 
FPC_HAS_* define necessary as by definition this can be done with 
version checks (there is only one trunk version, namely the current one).


- It should be decided if error messages should be specific for
the BASED construct or common to the ABSOLUTE one, slightly
rephrasing the error message.

Might be one or the other depending on the message.

- It should be decided if internal error # which currently keep
the same number of the nearby ABSOLUTE internal error should be
given new values.

Internal errors shall always be unique as they are used to find the 
error location, even for copy pasted code.




What's the rule to avoiding clashes? I gathered sort of MMDD## is it 
correct?


Giuliano



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Re: [fpc-devel] * GMX Spamverdacht * An extension of fpc language: the BASED construct

2017-12-26 Thread Giuliano Colla




Il 26/12/2017 18:43, Karoly Balogh (Charlie/SGR) ha scritto:

HI,

On Tue, 26 Dec 2017, Thorsten Engler wrote:


  Item: BYTE BASED ItemPtr;

Ignoring any other considerations for now, I would have at least used a
logical extension derived from already supported syntax:

Item: Byte absolute ItemPtr^;

As far as I understand (I did not try) this was once supported, but
explicitly removed by FPC 2.4.0 from Absolute keyword dereferencing is no
longer allowed:

http://wiki.freepascal.org/User_Changes_2.4.0#Absolute_variable_declarations

As the reasoning there shows, it's a very slippery slope this, which could
open a can of worms, so careful people. :)


I'd not be in favour of using the same syntax for two quite different 
beasts.
Although the practice implementation is similar, the semantics is 
completely different:


ABSOLUTE declares a variable whose storage is known and assigned at 
compile time.


BASED declares a variable whose storage is unknown, and will only be 
instantiated at run time.


Mixing the two things may cause a lot of troubles, and most likely 
that's the reason why it was removed from fpc 2.4.0.


Giuliano
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Re: [fpc-devel] An extension of fpc language: the BASED construct

2017-12-26 Thread Giuliano Colla




Il 26/12/2017 14:27, Mark Morgan Lloyd ha scritto:
What does gdb (and possibly other debuggers) make of this? 

What currently gdb tells (and any other debugger would tell) is :

No symbol "Item" in current context.

Once the appropriate entries are implemented in the debugger symbol 
table, it will behave like it does in similar conditions, i.e. 
displaying a value referenced by a pointer. I didn't mention in my ToDo 
list because I'm a bit lazy, but this too has to be done.
Is it really appropriate to declare Item as a variable, when it's 
really more akin to a macro? 

It's not different from the declarations:

myString: string;
myObject: TObject;

where your declaration only reserves a pointer, while the actual string 
or object will be instantiated only at run time.


Item is a variable, whose location isn't known at compile time, but will 
be known only at run time.


Giuliano

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Re: [fpc-devel] An extension of fpc language: the BASED construct

2017-12-26 Thread Thorsten Engler

In that case, if the functionality is going to be included, the best course of 
action might be to restore pre 2.4.0 behaviour, add the ability to use explicit 
dereference, and bind it to a separate mode switch.

Binding it to a mode switch solves the Delphi compatibility reason for removing 
it.
Allowing both explicit and implicit dereference solves the consistency reason 
for removing it.

And as Sven said, allowing absolute with expressions would be preferable to 
introducing a new keyword.

> -Original Message-
> From: fpc-devel [mailto:fpc-devel-boun...@lists.freepascal.org] On
> Behalf Of Karoly Balogh (Charlie/SGR)
> Sent: Wednesday, 27 December 2017 03:43
> To: FPC developers' list 
> Subject: Re: [fpc-devel] *** GMX Spamverdacht *** An extension of
> fpc language: the BASED construct
> 
> HI,
> 
> On Tue, 26 Dec 2017, Thorsten Engler wrote:
> 
> > >  Item: BYTE BASED ItemPtr;
> >
> > Ignoring any other considerations for now, I would have at least
> used
> > a logical extension derived from already supported syntax:
> >
> > Item: Byte absolute ItemPtr^;
> 
> As far as I understand (I did not try) this was once supported, but
> explicitly removed by FPC 2.4.0 from Absolute keyword dereferencing
> is no longer allowed:
> 
> http://wiki.freepascal.org/User_Changes_2.4.0#Absolute_variable_decl
> arations
> 
> As the reasoning there shows, it's a very slippery slope this, which
> could open a can of worms, so careful people. :)
> 
> Charlie
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Re: [fpc-devel] * GMX Spamverdacht * An extension of fpc language: the BASED construct

2017-12-26 Thread Karoly Balogh (Charlie/SGR)

HI,

On Tue, 26 Dec 2017, Thorsten Engler wrote:

> >  Item: BYTE BASED ItemPtr;
>
> Ignoring any other considerations for now, I would have at least used a
> logical extension derived from already supported syntax:
>
> Item: Byte absolute ItemPtr^;

As far as I understand (I did not try) this was once supported, but
explicitly removed by FPC 2.4.0 from Absolute keyword dereferencing is no
longer allowed:

http://wiki.freepascal.org/User_Changes_2.4.0#Absolute_variable_declarations

As the reasoning there shows, it's a very slippery slope this, which could
open a can of worms, so careful people. :)

Charlie
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Re: [fpc-devel] An extension of fpc language: the BASED construct

2017-12-26 Thread Sven Barth via fpc-devel

Am 26.12.2017 13:33 schrieb "Giuliano Colla" :

If the idea is not rejected, then a number of refinements (which I'm ready
to implement) are required to make the feature generally available:


My following remarks are independent of an eventual acceptance of the
feature :

- All architectures should be supported (now it's only for x86_64 -
symcpu.pas).

It might be possible to implement this in a platform independent way that
might simply need to expand the capabilites of "absolute".

- It should be decided if to make the feature generally available, or
conditioned by an {$IFDEF FPCHASBASED}

- It should be decided if the feature should be available in all modes or
only in a selected number of modes (what of TurboPascal Mode or Delphi
Mode?).

Rule of thumb: new features added as a separate mode switch, no FPC_HAS_*
define necessary as by definition this can be done with version checks
(there is only one trunk version, namely the current one).

- It should be decided if error messages should be specific for the BASED
construct or common to the ABSOLUTE one, slightly rephrasing the error
message.

Might be one or the other depending on the message.

- It should be decided if internal error # which currently keep the same
number of the nearby ABSOLUTE internal error should be given new values.

Internal errors shall always be unique as they are used to find the error
location, even for copy pasted code.

Regards,
Sven
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Re: [fpc-devel] * GMX Spamverdacht * An extension of fpc language: the BASED construct

2017-12-26 Thread Sven Barth via fpc-devel

Am 26.12.2017 14:44 schrieb "Thorsten Engler" :

>  Item: BYTE BASED ItemPtr;

Ignoring any other considerations for now, I would have at least used a
logical extension derived from already supported syntax:

Item: Byte absolute ItemPtr^;


I agree, as it avoids adding a new keyword (even if it is context
specific).

Regards,
Sven
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Re: [fpc-devel] An extension of fpc language: the BASED construct

2017-12-26 Thread Ozz Nixon

See: http://tutorial.modernpascal.com/?DataTypes

I implemented INTEGER as 32bit, but, if FPC makes it 16bit only, I will go
make the change right now. My end-users all know *DO NOT USE INTEGER* it's
even in the license agreement. "It is only there for make code compatible
w/ Delphi and FPC." I am still spending all my spare time to get MPC's
tutorial site up to par with FPC - as I promote MPC as FPC's Script Engine.

On Tue, Dec 26, 2017 at 8:50 AM, Ozz Nixon  wrote:

> I like the concept, I would like to ask that we do not support INTEGER as
> a type, and be more specific by limiting to SHORTINT, SMALLINT, LONGINT,
> INT64. That way code snippets are not confusing when you implement 16bit
> INT logic on a 32bit INT environment. Because I do a lot of documentation
> for n00bs in Pascal - the interchangeable INTEGER is probably one of
> Borland's biggest mistakes with the grammar! I would love to see FPC make
> the statement that the type INTEGER is 16bit only - deal with people
> freaking out for a year or two, and move the language forward. Even the
> INTEGER example here is assuming 16bit - which would be incorrect on 32bit
> platforms in specific $MODE. (may have picked wrong wording, however, I
> think everyone see's the point).
>
> Other than that, if FPC adds this, I will add it to Modern Pascal, so at
> least the two products are supporting "BASED".
>
> On Tue, Dec 26, 2017 at 8:27 AM, Mark Morgan Lloyd <
> markmll.fpc-de...@telemetry.co.uk> wrote:
>
>> On 26/12/17 12:45, Giuliano Colla wrote:
>>
>> /In short the BASED construct makes the C-style dereferencing operator
>>> unnecessary, by moving dereferencing from code to declaration.
>>>
>>> In fpc this translates into code looking like this, in this trivial
>>> example:
>>>
>>> var
>>>I: BYTE;
>>>I1: INTEGER;
>>>ItemPtr: Pointer;
>>>Item: BYTE BASED ItemPtr;
>>>IntegerItem: INTEGER BASED ItemPtr;
>>> 
>>>ItemPtr := @I;
>>>Item := $41;
>>> 
>>>ItemPtr := @I1;
>>>IntegerItem := -32767;
>>>
>>> This code will load the BYTE value $41 into the variable I, and the
>>> INTEGER value -32767 into the variable I1.
>>>
>>
>> What does gdb (and possibly other debuggers) make of this? Is it really
>> appropriate to declare Item as a variable, when it's really more akin to a
>> macro?
>>
>> --
>> Mark Morgan Lloyd
>> markMLl .AT. telemetry.co .DOT. uk
>>
>> [Opinions above are the author's, not those of his employers or
>> colleagues]
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>>
>
>
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Re: [fpc-devel] An extension of fpc language: the BASED construct

2017-12-26 Thread Ozz Nixon

I like the concept, I would like to ask that we do not support INTEGER as a
type, and be more specific by limiting to SHORTINT, SMALLINT, LONGINT,
INT64. That way code snippets are not confusing when you implement 16bit
INT logic on a 32bit INT environment. Because I do a lot of documentation
for n00bs in Pascal - the interchangeable INTEGER is probably one of
Borland's biggest mistakes with the grammar! I would love to see FPC make
the statement that the type INTEGER is 16bit only - deal with people
freaking out for a year or two, and move the language forward. Even the
INTEGER example here is assuming 16bit - which would be incorrect on 32bit
platforms in specific $MODE. (may have picked wrong wording, however, I
think everyone see's the point).

Other than that, if FPC adds this, I will add it to Modern Pascal, so at
least the two products are supporting "BASED".

On Tue, Dec 26, 2017 at 8:27 AM, Mark Morgan Lloyd <
markmll.fpc-de...@telemetry.co.uk> wrote:

> On 26/12/17 12:45, Giuliano Colla wrote:
>
> /In short the BASED construct makes the C-style dereferencing operator
>> unnecessary, by moving dereferencing from code to declaration.
>>
>> In fpc this translates into code looking like this, in this trivial
>> example:
>>
>> var
>>I: BYTE;
>>I1: INTEGER;
>>ItemPtr: Pointer;
>>Item: BYTE BASED ItemPtr;
>>IntegerItem: INTEGER BASED ItemPtr;
>> 
>>ItemPtr := @I;
>>Item := $41;
>> 
>>ItemPtr := @I1;
>>IntegerItem := -32767;
>>
>> This code will load the BYTE value $41 into the variable I, and the
>> INTEGER value -32767 into the variable I1.
>>
>
> What does gdb (and possibly other debuggers) make of this? Is it really
> appropriate to declare Item as a variable, when it's really more akin to a
> macro?
>
> --
> Mark Morgan Lloyd
> markMLl .AT. telemetry.co .DOT. uk
>
> [Opinions above are the author's, not those of his employers or colleagues]
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Re: [fpc-devel] * GMX Spamverdacht * An extension of fpc language: the BASED construct

2017-12-26 Thread Thorsten Engler

>  Item: BYTE BASED ItemPtr;

Ignoring any other considerations for now, I would have at least used a
logical extension derived from already supported syntax:

Item: Byte absolute ItemPtr^;



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Re: [fpc-devel] An extension of fpc language: the BASED construct

2017-12-26 Thread Mark Morgan Lloyd


On 26/12/17 12:45, Giuliano Colla wrote:

/In short the BASED construct makes the C-style dereferencing operator 
unnecessary, by moving dereferencing from code to declaration.


In fpc this translates into code looking like this, in this trivial example:

var
   I: BYTE;
   I1: INTEGER;
   ItemPtr: Pointer;
   Item: BYTE BASED ItemPtr;
   IntegerItem: INTEGER BASED ItemPtr;

   ItemPtr := @I;
   Item := $41;

   ItemPtr := @I1;
   IntegerItem := -32767;

This code will load the BYTE value $41 into the variable I, and the 
INTEGER value -32767 into the variable I1.


What does gdb (and possibly other debuggers) make of this? Is it really 
appropriate to declare Item as a variable, when it's really more akin to 
a macro?


--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]
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[fpc-devel] An extension of fpc language: the BASED construct

2017-12-26 Thread Giuliano Colla


  
  
Hi fpc developers,

here enclosed a patch to the compiler (and ppudump) to support
  the BASED construct (PL/1 and PL/M style), together with a patch
  to Lazarus codetools in order to be able to use it with Lazarus
  IDE.

For those unfamiliar with the BASED construct, here's a short
  description taken from Intel's PL/M-86 manual:
Based Variables
  Sometimes a direct reference to a PL/M-86 data element is either
  impossible or inconvenient. This happens for example, when the
  location of a data element must remain unknown until it is
  computed ad run time. In such cases, it may be necessary to write
  PL/M-86 code to manipulate the locations of data elements
  themselves.
To permit this type of manipulation PL/M-86 uses "based
  variables". A based variable is one that is pointed to by another
  variable called its "base". This means the base contains the
  address of the desired (based) variable.
  
In short the BASED construct makes the C-style dereferencing
operator unnecessary, by moving dereferencing from code to
declaration.

In fpc this translates into code looking like this, in this trivial
example:

var
  I: BYTE;
  I1: INTEGER;
  ItemPtr: Pointer;
  Item: BYTE BASED ItemPtr;
  IntegerItem: INTEGER BASED ItemPtr;

  ItemPtr := @I;
  Item := $41;

  ItemPtr := @I1;
  IntegerItem := -32767;

This code will load the BYTE value $41 into the variable I, and the
INTEGER value -32767 into the variable I1.
 

In more formal terms, the Declaration section of the fpc manual
should include a new path:

>--Variable modifiers -- based --  pointer -->
   |  |  |    | |
   |   -- PUint _expression_ ---| |
etc..



The main points are:

  
It doesn't break anything. - I have thoroughly tested it in
  my private fpc versions since fpc 2.2.4
  
  
Nobody is forced to use it: whoever doesn't like it can
  simply ignore its existence.
  
  
It provides a feature consistent with the general Pascal
  approach, to avoid whenever possible redundant dereferencing
  and typecasting, moving the tedious jobs from the developer 
  to the compiler.
  
  
It saves a number of C-style declarations, dereferencing and
  typecasting, and it provides a better type checking, making
  the code less error prone and much more readable and more
  "Pascalish".
  
  
It's very useful in message passing techniques, where
  different message types are funnelled to a single endpoint.
  Typically such messages are records composed by a fixed header
  which tells about the message type, followed by a variable
  content. They can be found everywhere, from IPC to X11
  interface to tcp/ip packets.

  
  I found it also useful in data entry applications, where
different fields require different data types.

The implementation is rather trivial: a BASED declaration is nothing
else than an ABSOLUTE declaration with an added dereferencing.
Therefore I've simply duplicated the code for the ABSOLUTE, with a
minimal change in pexpr.pas, and minimal adaptations elsewhere.
 
The enclosed patches are provided just to permit testing,
  evaluation and scrutiny from fpc maintainers. They only contain
  what is required for my personal usage.
 If the idea is not rejected, then a number of refinements (which
  I'm ready to implement) are required to make the feature generally
  available:
- All architectures should be supported (now it's only for x86_64
  - symcpu.pas).

- It should be decided if to make the feature generally
  available, or conditioned by an {$IFDEF FPCHASBASED}

- It should be decided if the feature should be available in all
  modes or only in a selected number of modes (what of TurboPascal
  Mode or Delphi Mode?).
- It should be decided if error messages should be specific for
  the BASED construct or common to the ABSOLUTE one, slightly
  rephrasing the error message.
- It should be decided if internal error # which currently keep
  the same number of the nearby ABSOLUTE internal error should be
  given new values.
- Maybe something else which I failed to notice.
I'd love to see my favourite programming language enriched by
  such a feature!
Giuliano



  

Index: nld.pas
===
--- nld.pas	(revisione 37753)
+++ nld.pas	(copia locale)
@@ -292,6 +292,8 @@
  case symtableentry.typ of
absolutevarsym :

Re: [fpc-devel] * GMX Spamverdacht * An extension of fpc language: the BASED construct

Re: [fpc-devel] An extension of fpc language: the BASED construct

Re: [fpc-devel] * GMX Spamverdacht * An extension of fpc language: the BASED construct

Re: [fpc-devel] An extension of fpc language: the BASED construct

Re: [fpc-devel] An extension of fpc language: the BASED construct

Re: [fpc-devel] * GMX Spamverdacht * An extension of fpc language: the BASED construct

Re: [fpc-devel] An extension of fpc language: the BASED construct

Re: [fpc-devel] * GMX Spamverdacht * An extension of fpc language: the BASED construct

Re: [fpc-devel] An extension of fpc language: the BASED construct

Re: [fpc-devel] An extension of fpc language: the BASED construct

Re: [fpc-devel] * GMX Spamverdacht * An extension of fpc language: the BASED construct

Re: [fpc-devel] An extension of fpc language: the BASED construct

[fpc-devel] An extension of fpc language: the BASED construct

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