DebugLn

From Free Pascal wiki

DebugLn is a LazLogger procedure that can assist debugging.

In your main program use code like:

program main;
uses
{$ifdef DEBUG}
  LazLogger;
{$end}

...

end.

In units where you need debugln-style debugging:

uses
{$ifdef DEBUG}
  LazLoggerBase;
{$else}
  LazLoggerDummy;
{$end}

procedure dosomething();
var
  s: string;
begin
...
  debugln( s );
...
end;

Syntax of debugln is comparable to writeln syntax.