View Source: Pascal - Waikato Linux Users Group

You are viewing an old revision of this page. View the current version.
An ImperativeProgrammingLanguage designed by NicolasWirth as a teaching language. Once very popular in schools before students started whining that they wanted to learn [C]. The ancestor of the language in [Borland]'s [Delphi] and [Kylix] [GUI] development environments, which added ObjectOrientation.

!!! A Sample

   __function__ plural (noun : __string__) : __string__;
      { Returns the plural version of a noun. }
   __var__
      i : integer;
   __begin__
      __case__ noun[[length(noun)] __of__
          's': __if__ noun[[length(noun)-1] = 'e' __then__
                  plural := noun
               __else__
                  plural := noun + 'es';
          'y': __begin__
                  delete(noun, length(noun), 1);
                  plural := noun + 'ies';
               __end__;
          __else__ plural := noun + 's';
      __end__;
   __end__; {plural}

(This is in the TurboPascal dialect of Pascal.)

!!! History

Pascal became popular very quickly because the original compiler was designed to be very easy to [port]. It was written in Pascal and compiled to [ByteCode]s, called ''P-Code''. All anyone had to do to get a Pascal compiler working on a new machine was to write the simple P-Code VirtualMachine for it -- they could hack the compiler around to generate proper MachineCode later. This meant that Pascal spread very quickly through the world's Universities. They began teaching in Pascal, because it was a very good language to demonstrate structured programming in -- a new idea and as such a hot topic at the time.

Standard Pascal was a nice language with terrible limitations: Pascal programs could not open files by name, could barely handle strings and could only pass arrays of predetermined sizes to functions. BrianKernighan famously described Pascal's problems in [Why Pascal is Not My Favorite Programming Language |http://www.lysator.liu.se/c/bwk-on-pascal.html]. It has to be noted that NicolasWirth had already addressed most of Pascal's problems in his follow-up language [Modula2] ''before'' BrianKernighan wrote this paper. In some places BrianKernighan seems to be just complaining that Pascal is not [C]. At any rate, these limitations meant that Pascal splintered into dialects as people hacked in missing features in incompatible ways. [C] did not have this problem, so it gradually took over from the Pascal dialects.

!!! Implementations

The Pascal grammer has maps very nicely to a RecursiveDescentParser struture and for this reason in it the language of choice when writing a RecursiveDescentParser by hand.

The most successful Pascal dialect has been Borland's TurboPascal. There are two OpenSource Pascal compilers for [Linux]:

* [GNU Pascal | http://www.gnu-pascal.de/]
* [Free Pascal | http://www.freepascal.org/]

Free Pascal tends more towards TurboPascal compatibility.

The online book [Pascal Implementation: A Book and Sources | http://www.cwi.nl/~steven/pascal/] walks you through the source code to the original Pascal compiler. It's educational to read just as an extended critique of a non-trivial program.

-----
CategoryProgrammingLanguages, CategoryImperativeProgrammingLanguages, CategoryMachineOrientedProgrammingLanguages
14 pages link to Pascal:
Version 15, saved on Wednesday, November 19, 2003 5:47:26 pm by AristotlePagaltzis
Edit PageHistory Diff Info LikePages