Pascal basics

A PXX Pascal program has a program header, declarations, and a main block:

program demo;

var
  name: string;

begin
  name := 'PXX';
  writeln('Hello from ', name);
end.

Statements are separated with semicolons. The program ends with end..

Declarations

Common declaration sections are:

const
  Answer = 42;

type
  TPoint = record
    X, Y: Integer;
  end;

var
  P: TPoint;

PXX supports the usual Pascal statement forms:

if P.X = 0 then
  writeln('origin')
else
  writeln('not origin');

while P.X < 10 do
  Inc(P.X);

for P.Y := 1 to 3 do
  writeln(P.Y);

case selects on an ordinal value. The default branch may be introduced with either else or its synonym otherwise:

case P.X of
  0:    writeln('zero');
  1, 2: writeln('small');
otherwise
  writeln('large');
end;

Procedures do not return a value. Functions assign their return value through Result:

function Twice(N: Integer): Integer;
begin
  Result := N * 2;
end;

Parameters can be passed by value, const, var, or out, depending on the routine contract.

Reusable code lives in units and is imported with uses:

program app;
uses sysutils;
begin
  writeln(IntToStr(123));
end.

The pxx wrapper created by install.sh adds the bundled library roots, so project units can usually be found without extra flags.