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Pascal

Pascal is a procedural programming language created by Niklaus Wirth in 1970.

Pascal was a popular choice for microcomputers in the 70's and 80's, even more popular than C initially (C was still quite an UNIX-only language) due to its simple design, which allowed fast simple single-pass compilers. Later on in the mid-80s and early-90s Pascal began losing its dominance to C, mainly because of the influence of OSes of that time, which were all written in C.

In its "vanilla" form, Pascal is not any more complex than C, aside from having features that C doesn't have, such as range types, nested procedures, sets, builtin tagged unions, etc.

Pascal has two ISO standards: ISO 7185, informally named "Standard Pascal" an ISO 10206, named "Extended Pascal". Because the Pascal described in the ISO 7185 standard is quite useless for practical programming, most compilers are for an extended superset of the Pascal described in that standard. A more useful Pascal is described on the "Extended Pascal" standard, but by the time it came out it was quite late.

Compilers

  • FPC (Free Pascal Compiler): currently the most popular Pascal compiler with wide support for different OSes and architectures, libre software.
  • GNU Pascal: frontend for GCC, abandoned.
  • Turbo Pascal: old compiler for DOS systems, proprietary.
  • Delphi: proprietary, adds OOP bloat and exception handling.

Notes

Returning values from functions

{ The "classical" way, assigning the return value to the function name }
function Square(n: integer): integer;
begin
    Square := n * n; 
end;

{ Object Pascal and Delphi, assigning to special `Result` variable }
{ Enable with `-S2` in FPC }
function Square(n: integer): integer;
begin
    Result := n * n; 
end;

{ Return statement like }
function Square(n: integer): integer;
begin
    Exit(n * n);
end;

Identifiers

Pascal is case-insensitive, so WriteLn, writeLn, writeln and wRiTeLn are the same identifiers.

Examples

Hello world

program HelloWorld;

begin
    writeLn('Hello, World!');
end.

And then compile:

fpc hellopascal.pas

Factorial

program Factorial;

{ qword = 64 bit unsigned type }
function factorial(n: qword): qword;
begin
    Result := 1;
    while n > 0 do
    begin
        { The usage of C-like arithmetic assignment operators is possible with -Sc: }
        { Result *= n; }
        Result := Result * n;
        dec(n); { equivalent to C's `--` operator }
    end;
end;

var
    n: qword;
    values: array of qword = (14, 5, 2, 10, 1, 18, 4);
begin
    for n in values do
    begin
        writeLn('Factorial of ', n, ' = ',  factorial(n));
    end;
end.

Compiling:

fpc -O3 -S2 fact.pas

Resources

See also