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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

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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

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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

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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/

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Re: GPC MANUAL: Schemata, Pointer arithmetics
by Frank Heckenbach 03 Jun '98

03 Jun '98

Peter Gerwinski wrote: > here are three new sections for the "programmer's guide to GPC" (see > `info -f gpc -n programming'). Comments/improvements/etc. welcome. OK, here they are. :-) > @node Schemata > [...] > Schemata are types that depend on a variable, called ``discriminant''. <nitpick> There can be more than one discriminant. </nitpick> > @node Pointer arithmetics > [...] > @smallexample > Var > A: array [ 1..7 ] of Char; > p, q: ^Char; > i: Integer; > > [...] > > for p:= @@A [ 1 ] to @@A [ 7 ] do > p^:= 'x'; > > q:= @@A [ 3 ]; > while p > q do This is a bad example, IMHO, since p is defined as being undefined after a for loop, AFAIK -- even if it might actually have the correct value here. > begin > p^:= 'y'; > dec ( p ); > end (* while *); > > i:= q - p; This would, after the above while loop, always be 0, and is therefore not very instructive, I think. > @node Type casts This section does not clearly draw the distinction between value type casting and variable type casting. So I'll try to write an improvement of this section (it got a little bit longer ;-): @c ============================================================================ @node Type casts @section Type Casts @cindex type casts In some cases, especially when interfacing with other languages, Pascal's strong typing can be an obstacle. To temporarily circumvent this, GPC (and other Pascal compilers) defines explicit ``type casts''. There are two kinds of type casts, value type casts and variable type casts. Value type casts To convert a value of one data type into another type, you can use the target type like the name of a function that is called. The value to be converted can be a variable or an expression. An example: @smallexample Var Ch: Char; i: Integer; [...] i := Integer (Ch); @end smallexample Another, more complicated, example: @smallexample Type CharPtr = ^Char; CharArray = array [ 0..99 ] of Char; CharArrayPtr = ^CharArray; Var Foo1, Foo2: CharPtr; Bar: CharArrayPtr; [...] @{$X+@} @{ We need extended syntax in order to use ``Succ'' on a pointer @} Foo1 := CharPtr ( Bar ); Foo2 := CharPtr ( Succ ( Bar ) ); @end smallexample However, because of risks involved with type casts, explained below, you should try to avoid type casts whenever possible -- and it should be possible in most cases. For instance, the first example above could use the built-in function ``Ord'' instead of the type cast: @smallexample i := Ord (Ch); @end smallexample The assignments in the second example could be written in the following way without any type casts: @smallexample Foo1 := @@Bar^ [ 0 ]; Foo2 := @@Bar^ [ 1 ]; @end smallexample Value type casting only works between certain types: either between different ordinal types (including integer types), or between different real types, or between different pointer types. In each case, the actual value, i.e. the ordinal or numeric value or the address pointed to, respectively, is preserved in the cast. Note: It is also possible to cast from an integer into a real type. This is a consequence of the fact that integer values are generally automatically converted to real values when needed. Note: In the case of pointers, a warning is issued if the dereferenced target type requires a bigger alignment than the dereferenced source type (see @ref{alignment}). Variable type casts It is also possible to temporarily change the type of a variable, without converting its contents in any way. This is called variable type casting. The syntax is the same as for value type casting. This can be confusing, as the example below shows. The type-casted variable is still the same variable (memory location) as the original one, just with a different type. Outside of the type cast, the variable keeps its original type. There are some important differences between value and variable type casting: - Variable type casting only works on variables, not on expressions. - The result of a variable type casting is still a variable. Especially, it can be used on the left side of an assignment (as a so-called ``lvalue''), or passed by reference to a procedure. - No values are converted. The contents of the variable, seen as a raw bit pattern, are just interpreted according to the new type. In many cases, this does not make a big difference, e.g. the same ordinal values of different ordinal types have the same bit pattern (provided, the types have the same size), and similarly for different pointer types. However, there are cases where it does make a difference, most notably the completely different internal representation of integer and real types. This is demonstrated in the following example, admittedly a very constructed example, by using an integer and a real type of the same size and trying to cast between them. - Because bit patterns are just interpreted differently, the source and target type must have the same size. If this is not the case, GPC will give a warning. (@@error? see below) - Beware: Variable type casts might have unexpected effects on different platforms since you cannot rely on a specific way the data is stored (e.g. see @ref{endianness}). @smallexample program TypeCastingTraps; { Declare a real type and an integer type of the same size, and some variables of these types we will need. } Type RealType = ShortReal; IntegerType = Integer ( BitSizeOf ( RealType ) ); Var i, i1, i2, i3, i4, i5: IntegerType; r, r1, r2, r3, r4: RealType; begin @{ First part: Casting integer into real types. @} @{ Start with some integer value @} i := 42; @{ First attempt to cast. Here, an lvalue is casted, so this must be a variable type cast. Therefore, the bit pattern of the value of i is transferred unchanged into r1 which results in a silly value of r1. @} IntegerType (r1) := i; @{ Second try. Here we cast an expression -- though a trivial one --, rather than a variable. So this can only be a value type cast. Therefore, the numeric value is preserved, i.e. r2 = 42.0 . @} r2 := RealType (i+0); @{ Third way. In this last example, a variable is casted, and the result is used as an expression, not as an lvalue. So this could be either a value or variable type cast. However, there is a rule that value type casting is preferred if possible. So r3 will contain the correct numeric value, too. @} r3 := RealType (i); @{ Of course, you do not need any casts at all here. A simple assignment will work because of the automatic conversion from integer to real types. So r4 will also get the correct result. @} r4 := i; @{ Now the more difficult part: Casting real into integer types. @} @{ Start with some real value. @} r := 41.9; @{ Like the first attempt above, this one does a variable type cast, preserving bit patterns, and leaving a silly value in i1. @} RealType (i1) := r; @{ The second try from above does not work, because an expression of type real is to be casted into an integer which is not allowed. @} @{ i2 := IntegerType (r+0); @} @{ Third way. This looks just like the third way in the first part which was a value type cast. But -- surprise! Since value type casting is not possible from real into integer, this really does a variable type casting, and the value of i3 is silly again! This difference in behaviour shows some of the hidden traps in type casting. @} i3 := IntegerType (r); @{ As often, it is possible to avoid type casts altogether and convert real types into integers easily by other means, i.e. by using the built-in functions ``Round'' or ``Trunc'', depending on the mode of rounding one wants. @} i4 := Round (r); @{ 42 @} i5 := Trunc (r); @{ 41 @} end. @end smallexample When dealing with objects (see @ref{OOP}), it is often necessary---and safe---to cast a pointer to an object into a pointer to a more specialized (derived) object. In future releases, GPC will provide an operator @samp{as} for a safer approach to this problem. See also: @ref{absolute}, @ref{alignment}, @ref{endianness}, @ref{OOP}, @ref{Ord}, @ref{Chr}, @ref{Round}, @ref{Trunc}. @c ============================================================================ Some notes: - My texi skills are quite limited. In particular I think I should - highlight the headings "value"- and "variable type casting" - mark the "Note:"'s specially and - format the enumeration better than with "-"'s, but I wanted to get this out tonight, so I didn't look up how to do it. - When writing this, I strongly thought there should be a way to mark certain sections as "advanced" and "very advanced"... :-) - I'm not completely sure about the kind of types between which value type casting works, with "works" in the sense of (either or all): supported by BP, supported by GPC currently, should be supported by GPC. This is left to be checked and corrected if necessary. - Unfortunately, GPC does not behave completely like I described it :-(, but I think wrongly so. In particular, for the line "RealType (i1) := r;", it does a value type cast which is IMHO wrong since it is an lvalue. So I consider it a bug in GPC, tested by the following program, very similar to the one above, without comments: program frank170; Type RealType = ShortReal; IntegerType = Integer ( BitSizeOf ( RealType ) ); Var r, r1, r2, r3, r4: RealType; i, i1, i2, i3, i4, i5: IntegerType; begin i := 42; IntegerType (r1) := i; r2 := RealType (i+0); r3 := RealType (i); r4 := i; r := 41.9; RealType (i1) := r; i3 := IntegerType (r); i4 := Round (r); { 42 } i5 := Trunc (r); { 41 } if (r1<>42) and (r2=42) and (r3=42) and (r4=42) and (i1<>41) and (i1<>42) and (i3<>41) and (i3<>42) and (i4=42) and (i5=41) then writeln('OK') else writeln('Failed') end. - I think, GPC should give an error, not just a warning, when casting between types of different size -- at least in {$x-} mode. With extended syntax active (or some other switch), a warning still seems appropriate. Of course: Comments/improvements/etc. welcome! Frank -- 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

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Re: GPC test suite (was: egcs-19980517 and gpc-980511)
by mrs＠wrs.com 02 Jun '98

02 Jun '98

> From: Peter Gerwinski <peter(a)gerwinski.de> > Date: Tue, 2 Jun 1998 10:44:24 +0200 (MEST) > Yes: The program contains a comment of the form > (* FLAG --extended-pascal --pedantic -Werror *) > which carries the flags that must be passed to the call to `gpc' > for that the test makes sense. Gee, this exactly mirrors the g++ testsuite. We spell it: // Special g++ Options: -pedantic -Werror

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gpc-bug
by Matthias Klose 02 Jun '98

02 Jun '98

A user reported this bug with gpc-980511, built with the egcs-19980525 snapshot on a Debian/Linux 2.0 system: % cat typrat.pas Unit typrat ; INTERFACE Type TRATIONNEL = Record num : integer ; den : integer ; end ; IMPLEMENTATION END. % cat meo_rat.pas unit meo_rat ; INTERFACE uses typrat in 'typrat.pas'; procedure AffichRat(a : Trationnel) ; IMPLEMENTATION procedure AffichRat(a : Trationnel) ; begin end ; END. % gpc -c typrat.pas % gpc -c meo_rat.pas gpc: Internal compiler error: program gpc1 got fatal signal 11 I hope that this is enough information to reproduce the bug. If not, please ask.

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GPC REFERENCE: ParamCount...
by Orlando Llanes 02 Jun '98

02 Jun '98

Is there a way to retrieve the number of parameters using GPC? See ya! Orlando Llanes "Meine Damen und Herren, Elvis hat soeben das Gebaeude verlassen!" "Look out fo' flyeeng feet" O__/ a010111t(a)bc.seflin.org \/|____. O <__. \/\> / \ ____________|___\______ http://ourworld.compuserve.com/homepages/Monkey414

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GPC REFERENCE: abs
by Peter Gerwinski 02 Jun '98

02 Jun '98

Hi! This is an example entry for how I think our joined effort to complete the GPC reference could work. The section I am posting is already in existence (`abs'): @c ---------------------------------------------------------------------------- @node abs @unnumberedsec abs @cindex abs @unnumberedsubsec Syntax @smallexample Function abs ( i: @var{integer type} ): @var{integer type}; @end smallexample or @smallexample Function abs ( x: @var{real type} ): @var{real type}; @end smallexample or @smallexample Function abs ( z: @var{complex type} ): @var{real type}; @end smallexample @unnumberedsubsec Description Returns the absolute value of the argument: @smallexample Function abs ( x: @var{some type} ): @var{some type}; begin (* abs *) if x < 0 then abs:= -x else abs:= x; end (* abs *); @end smallexample @unnumberedsubsec Standards The function @samp{abs} is defined in ISO-7185 Standard Pascal; its application to complex values is defined in ISO-10206 Extended Pascal. @unnumberedsubsec Example @smallexample Program TestAbs; Var i1: Complex; begin writeln ( abs ( 42 ) ); (* 42 *); writeln ( abs ( -42 ) ); (* 42 *); writeln ( abs ( -12.1 : 0 : 1 ) ); (* 12.1 *); i1:= cmplx ( 1, 1 ); (* 1 + i *) writeln ( abs ( i1 ) : 0 : 10 ); (* yields 1.4142135624, i.e. sqrt ( 2 ) *) end. @end smallexample @unnumberedsubsec See also @ref{sqr}. @c ---------------------------------------------------------------------------- If you follow-up to this mail and modify the section, please include a complete copy without leading "> " or such in order to make it easier for me to integrate the modified copy into `reference.texi'. Peter PS: I just was pointed to some errors in the above, so you can expect my own follow-up to this in a few minutes. :-) -- 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/

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Re: egcs-19980517 and gpc-980511
by mrs＠wrs.com 02 Jun '98

02 Jun '98

> From: Matthias Klose <Matthias.Klose(a)cs.tu-berlin.de> > Date: Fri, 22 May 1998 04:43:56 +0200 (MET DST) > To: egcs(a)cygnus.com, gpc(a)hut.fi > After patching the gpc-980511 drop in for egcs, I got a working > egcs-gpc compiler. Some problems remain: > - the gpc testsuite fails with dejagnu-971222, it runs ok with dejagnu-1.3 1.3 is horribly old, and I don't recommend you use it. dejagnu needs a new FSF release to incorporate all the latest good bits that people have put into it. All the people that use dejagnu, use newer snapshots. Please consider upgrading to dejagnu-971222.

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