GET chnl-exp [, position-clause ] [, lock-clause ]

                         { RFA rfa-var      }
        position-clause: { RECORD num-exp   }
                         { KEY # key-clause }

        lock-clause:  { ALLOW allow-clause [WAIT [int-exp]] }
                      { WAIT [int-exp]                      }
                      { REGARDLESS                          }

                       { NONE   }
        allow-clause:  { READ   }
                       { MODIFY }

                                     { str-exp      }
        key-clause:  int-exp1 rel-op { int-exp2     }
                                     { decimal-exp  }
                                     { quadword-exp }

                 { EQ }
        rel-op:  { GE }
                 { GT }
                 { NX }
                 { NXEQ }