RECURSIVE-DESCENT PARSER FOR PL/0 IN PSEUDO-CODE
                ------------------------------------------------


          procedure PROGRAM;
              begin
                  GET_TOKEN;
                  BLOCK;
                  if TOKEN <> "." then ERROR
              end;

          procedure BLOCK;
              begin
                  if TOKEN = "const" then begin
                      repeat
                          GET_TOKEN;
                          if TOKEN <> IDENT then ERROR;
                          GET_TOKEN;
                          if TOKEN <> "=" then ERROR;
                          GET_TOKEN;
                          if TOKEN <> NUMBER then ERROR;
                          GET_TOKEN
                      until TOKEN <> ",";
                      if TOKEN <> ";" then ERROR;
                      GET_TOKEN
                  end;
                  if TOKEN = "var" then begin
                      repeat
                          GET_TOKEN;
                          if TOKEN <> IDENT then ERROR;
                          GET_TOKEN
                      until TOKEN <> ",";
                      if TOKEN <> ";" then ERROR;
                      GET_TOKEN
                  end;
                  while TOKEN = "procedure" do begin
                      GET_TOKEN;
                      if TOKEN <> IDENT then ERROR;
                      GET_TOKEN;
                      if TOKEN <> ";" then ERROR;
                      GET_TOKEN;
                      BLOCK;
                      if TOKEN <> ";" then ERROR;
                      GET_TOKEN
                  end;
                  STATEMENT
              end;



















          procedure STATEMENT;
              begin
                  if TOKEN = IDENT then begin
                      GET_TOKEN;
                      if TOKEN <> ":=" then ERROR;
                      GET_TOKEN;
                      EXPRESSION
                  end
                  else if TOKEN = "call" then begin
                      GET_TOKEN;
                      if TOKEN <> IDENT then ERROR;
                      GET_TOKEN
                  end
                  else if TOKEN = "begin" then begin
                      GET TOKEN;
                      STATEMENT;
                      while TOKEN = ";" do begin
                          GET_TOKEN;
                          STATEMENT
                      end;
                      if TOKEN <> "end" then ERROR;
                      GET_TOKEN
                  end
                  else if TOKEN = "if" then begin
                      GET_TOKEN;
                      CONDITION;
                      if TOKEN <> "then" then ERROR;
                      GET_TOKEN;
                      STATEMENT
                  end
                  else if TOKEN = "while" then begin
                      GET_TOKEN;
                      CONDITION;
                      if TOKEN <> "do" then ERROR;
                      GET_TOKEN;
                      STATEMENT
                  end
              end;






























          procedure CONDITION;
              begin
                  if TOKEN = "odd" then begin
                      GET_TOKEN;
                      EXPRESSION
                  else begin
                      EXPRESSION;
                      if TOKEN <> RELATION then ERROR;
                      GET_TOKEN;
                      EXPRESSION
                  end
              end;

          procedure EXPRESSION;
              begin
                  if TOKEN = ADDING_OPERATOR then GET_TOKEN;
                  TERM;
                  while TOKEN = ADDING_OPERATOR do begin
                      GET_TOKEN;
                      TERM
                  end
              end;

          procedure TERM;
              begin
                  FACTOR;
                  while TOKEN = MULTIPLYING_OPERATOR do begin
                      GET_TOKEN;
                      FACTOR
                  end
              end;

          procedure FACTOR;
              begin
                  if TOKEN = IDENTIFIER then
                      GET_TOKEN
                  else if TOKEN = NUMBER then
                      GET_TOKEN
                  else if TOKEN = "(" then begin
                      GET_TOKEN;
                      EXPRESSION;
                      if TOKEN <> ")" then ERROR;
                      GET_TOKEN
                  end
                  else ERROR
              end;