source: branches/interpreter/interpreter2/interpreter.lpr

program interpreter;

function IsWhiteSpace(C: Char): Boolean;
begin
  Result := (C = ' ') or (C = #13) or (C = #10) or (C = #9);
end;

procedure ShowError(Text: string);
begin
  WriteLn(Text);
  Halt;
end;

function ReadChar: Char;
begin
  if Eof then ShowError('Premature end of source');
  Read(Result);
end;

function ReadNext: string;
var
  C: Char;
begin
  Result := '';
  C := ReadChar;
  while IsWhiteSpace(C) do C := ReadChar;
  while not IsWhiteSpace(C) do begin
    Result := Result + C;
    C := ReadChar;
  end;
end;

procedure Expect(Text: string);
var
  Next: string;
begin
  Next := ReadNext;
  if Next <> Text then
    ShowError('Expected ' + Text + ' but found ' + Next);
end;

begin
  WriteLn('Start');
  Expect('begin');
  Expect('end.');
  WriteLn('Finished');
end.
{
|begin
|end.
}