Gpc June 1998

gpc@gnu.de

38 participants
59 discussions

Re: GPC REFERENCES: do
by Frank Heckenbach 03 Jun '98

03 Jun '98

Miklos Cserzo wrote: > The later form is for easy access of fields of record or schema type > variables. or object type -- Frank Heckenbach, frank(a)pascal.gnu.de http://fjf.gnu.de/ PGP keys: http://pgp5.ai.mit.edu/pks/lookup?op=index&search=Frank+Heckenbach

1 0

Re: GPC REFERENCE: repeat
by Frank Heckenbach 03 Jun '98

03 Jun '98

Miklos Cserzo wrote: > "repeat" is reserved word in all Pascal dialects for creating loops in the ^a > program execution. The statements after the "repeat" executed ^are > sequentially. When the "until" statement reached the execution continues ^is > with the next statement if the boolean expression evaluates "true". If it > is "false" the execution continues at the next statement after the ^^^^first(?) > starting "repeat" of the loop and the enclosed statements will be executed > again. > > The statements in the loop will be executed at least once. If the > expression in the "until" statement always "false" the execution falls ^is > into infinite loop. ^an > It is allowed the create nested "repeat - until" loops where the closest ^^^to > .... > repeat { echo the input from "infile" to "outfile" } > readln(infile,buffer); > writeln(outfile,buffer); > until eof(infile); > close(infile); close(outfile); > .... IMHO a bad example for repeat, better suited for a while loop, since infile can be empty. -- Frank Heckenbach, frank(a)pascal.gnu.de http://fjf.gnu.de/ PGP keys: http://pgp5.ai.mit.edu/pks/lookup?op=index&search=Frank+Heckenbach

1 0

Re: GPC REFERENCE: for
by Kevin A. Foss 03 Jun '98

03 Jun '98

On Wed, 3 Jun 1998 18:54:27 +0200 (MEST), Peter Gerwinski wrote: >According to Miklos Cserzo: >> After the execution of the loop the value of the control variable is >> undefined. > >While this is stated in ISO-10206 I have seen some ISO-7185 test programs >that require the value to be <final_value>. Somebody knows definitly? ISO 7185:6.8.3.9 says that it should be undefined, unless the loop is exited via a goto. (This same discussion came up recently on c.l.p.ansi-iso, so I'm fairly sure of this... don't have the standard in front of me right as I write this :) ) >> A proper code should not relay on that value. I agree with this, so I'm interested to hear about the test programs you have that rely on post loop values of the control variable. Perhaps this is something that wasn't enforced in early Pascal implementations and later was codified in the standard. >(You see: The "Standards" section is taking over ... ;-) > >(You also see why I am so slow in writing documentation. ;-)-: I think this might be the best benefit of the current process of having everyone post their entries to the list. Partially so others can comment on other standards that the author of each section might not be familiar with, and partially so the developers can comment on any extra GPC-specific features that might also be available. -Kevin -- Kevin A. Foss -- kfoss(a)mint.net

1 0

Subject: Re: GPC REFERENCES: do
by Frank Heckenbach 03 Jun '98

03 Jun '98

(* The subject line is misleading now since this will be in the "to begin"/ "to end" sections, but I kept it anyway. *) > to begin do statement; > or ^ Better mention it with or without this one? > to end do statement; In this case, I'd say, with the semicolon, since the semicolon is necessary because of the "to begin do". In other cases, like the various loops, there should be -- strictly speaking -- no semicolon at the end, because it's not required by the loop, and actually doesn't have to be there (e.g. before an "end" or an "else" that belongs to a "case"), and sometimes even must not be there (before an "else" that belongs to an "if"). -- Frank Heckenbach, frank(a)pascal.gnu.de http://fjf.gnu.de/ PGP keys: http://pgp5.ai.mit.edu/pks/lookup?op=index&search=Frank+Heckenbach

1 0

Subject: Re: GPC REFERENCE: for
by Frank Heckenbach 03 Jun '98

03 Jun '98

Just some spelling corrections and such... > variable set to the initial value then incremented by 1 after each ^is > loop executed ones. If the initial value higher than the final value the ^s ^^^^once ^is > body of the "do" statement not executed. ^is > In the second form of the command the control variable decremented by 1 in ^is > inside the loop. The code that violate that rule will compile and run - if ^^^() ^s > After the execution of the loop the value of the control variable is > undefined. A proper code should not relay on that value. ^^^^^rely -- Frank Heckenbach, frank(a)pascal.gnu.de http://fjf.gnu.de/ PGP keys: http://pgp5.ai.mit.edu/pks/lookup?op=index&search=Frank+Heckenbach

1 0

GPC REFERENCE: begin
by Miklos Cserzo 03 Jun '98

03 Jun '98

begin SYNTAX: begin statement1; statement2; .... end; DESCRIPTION: "begin" is word-symbol (reserved word) in all Pascal standards. "begin" with its enclosing "end" groups together the statements between them so they are treated as one single statement during the execution. Wherever the Pascal syntax requires one statement "begin" ... "end" constructions can be used. (It is allowed to use empty statement: "begin end;".) The execution part of a program block syntactically is a single statement therefore should be enclosed into a "begin ... end." construction. This apply to the execution part of procedures and functions as well. It is a syntax error having a "begin" without an enclosing "end". STANDARDS: all EXAMPLE: var ok:boolean; ... if not ok then begin writeln('Error occurred, execution aborted.'); halt; end; SEE ALSO: end, for, while, do _________________________ Comment this please. miklos

2 1

GPC REFERENCES: do
by Miklos Cserzo 03 Jun '98

03 Jun '98

do SYNTAX: for iteration_variable := initial_value to final_value do statement or for iteration_variable := initial_value downto final_value do statement or while boolean_expression do statement or with list_element[,...] do statement DESCRIPTION: "do" is a reserved word in all Pascal standards. It is used for constructing loops during the execution with "for" and "while" statements. The statement following the "do" - the body of the "do" statement - will be executed in cycles according to the controlling iteration variable or boolean expression respectively. Often several simple statements grouped together in a compound-statement as the body of the cycle ("begin statement1; statement2;.... end;"). The later form is for easy access of fields of record or schema type variables. The references in the body of the "do" statement will access the corresponding fields directly in the listed record or schema identifiers. ***** it is rather cryptic. I hardly ever use this feature. correct this section ***** STANDARDS: All. EXAMPLE: See the section of the reference under "for", "while" and "with" for the examples. SEE ALSO: for, while, with ____________________________________ I am waiting for comments. miklos

2 1

Re: GPC REFERENCES: do
by Miklos Cserzo 03 Jun '98

03 Jun '98

On Wed, 3 Jun 1998, Nick Burrett wrote: > If we are going to supply syntax to Pascal constructs then I suggest > that they are suppled as proper grammar i.e. the LALR(1) format. Can you point me to good description? My searches on the net did not bring up anything useful. miklos

1 0

GPC REFERENCE: repeat
by Miklos Cserzo 03 Jun '98

03 Jun '98

repeat SYNTAX: repeat statement1; statement2; ... until boolean_expression; DESCRIPTION: "repeat" is reserved word in all Pascal dialects for creating loops in the program execution. The statements after the "repeat" executed sequentially. When the "until" statement reached the execution continues with the next statement if the boolean expression evaluates "true". If it is "false" the execution continues at the next statement after the starting "repeat" of the loop and the enclosed statements will be executed again. The statements in the loop will be executed at least once. If the expression in the "until" statement always "false" the execution falls into infinite loop. It is allowed the create nested "repeat - until" loops where the closest appearance of the keywords will define the individual loops. It is a syntax error if the number of "repeat"-s and "until"-s are different in a program block. STANDARDS: All EXAMPLE: .... repeat { echo the input from "infile" to "outfile" } readln(infile,buffer); writeln(outfile,buffer); until eof(infile); close(infile); close(outfile); .... This code is equivalent to the following: label 10; ... 10 readln(infile,buffer); writeln(outfile,buffer); if not eof(infile) then goto 10; close(infile); close(outfile); ... SEE ALSO: for, while, do _________________________________ Comment this please. miklos

1 0

Let's write the GPC reference together! (was: gpc-980511 build bug)
by Peter Gerwinski 03 Jun '98

03 Jun '98

Hi, everybody! Miklos Cserzo wrote: > > Before the official release we should do something about the documentation. > It is really poor. Some 160 pages are missing from the language reference. > That is definitely too much writing for a single person but with a joint > effort it should not be a problem. How about to post the missing sections > of the reference to the list? I consider this a VERY GOOD idea! While some nice people are already working on improving the documentation, a joint effort will certainly yield a faster and better result. Of course, such a project must be coordinated; otherwise we will end up with a lot of incompatible fragments. Here are my thoughts about how to do that: * Everyone is encouraged to write or improve sections of the GPC reference, `reference.texi'. The article should be mailed to this list with a subject like GPC REFERENCE: abs It must contain a complete section of `reference.texi' in the standardized format (GNU Texinfo) *including* the separator lines beginning with `@c'. I will post a real-world example in a few minutes. For a description of the GNU Texinfo format, type `info -f texinfo'. * When replying and improving the text, always include a complete snippet as described above without leading `> ' or such. This is to simplify integration into the file `reference.texi'. * Spelling corrections are welcome. And now for some guidelines how the documentation should look like: * Be exact. Examples must work. * Really explain it. "Help" screens like "Use the `Procedure' keyword to declare a procedure" do not help anyone. *Nothing* is self-evident. * Give examples. Besides a tiny easy-to-understand example there should always be a real-world example that helps to avoid pitfalls. (See `info -f gpc -n and' for an example: The first `if' is the easy example, while the `else if' describes a common pitfall. Maybe it would be even better to separate them ...) * Use cross references. When a cross reference appears in the help text, it is usually desirable to repeat it in the `See also' subsection. * Be technical, not personal. For example, I do not like `goto', and I never use it in my programs, but if I explain it, this does not matter. If there are some *technical* drawbacks using `goto' I can mention them, but a sentence telling "better don't use `goto'" causes nothing but confusion. * Read the tips in `info -f texinfo -n Tips'. Comments? An example of what I mean will follow in a few minutes. Also, I am uploading the file `reference.texi' to ftp://agnes.dida.physik.uni-essen.de/gnu-pascal/alpha/reference.texi so you do not need to download the whole GPC source just to get your hands on that single file. Peter -- Peter Gerwinski, Essen, Germany, http://home.pages.de/~Peter.Gerwinski/ Maintainer GNU Pascal - http://home.pages.de/~GNU-Pascal/ - gpc-980511 PGP key on request - 6C 94 45 BE 28 A4 96 - 0E CC E9 12 47 25 82 75 Fight the SPAM and UBE! - http://spam.abuse.net/ - http://maps.vix.com/

2 5

2024

2023

2022

2021

2020

2019

2018

2017

2016

2015

2014

2013

2012

2011

2010

2009

2008

2007

2006

2005

2004

2003

2002

2001

2000

1999

1998

1997

1996

1995

Gpc June 1998