ligo/src/proto_alpha/lib_protocol/test/contracts/concat.tz

parameter string;
storage string;
code {DUP;                      # We're going to need both the storage and parameter
      CAR;                      # Get the parameter
      DIP{CDR};                 # Get the storage value
      SWAP;                     # Get the order we want (this is optional)
      CONCAT;                   # Concatenate the strings
      NIL operation; PAIR}      # Match the calling convention