snippet6.tz

# This contract is an update of the counter.tz contract.
# It now keep the previous counter before each update.
# It has two entrypoints :
#  - increaseCounterBy : storage.previousCounter = storage.counter, storage.counter = storage.counter + value
#  - decreaseCounterBy : storage.previousCounter = storage.counter, storage.counter = storage.counter - value

parameter (or (int %increaseCounterBy) (int %decreaseCounterBy));
storage (pair (int %counter) (int %previousCounter));
code {
  UNPAIR;
  SWAP;
  CAR @newPreviousCounter;
  SWAP;
  DIP { DUP @currentCounter; };
  IF_LEFT {
    ADD @newCounter;
  }
  {
    SWAP;
    SUB @newCounter;
  };
  PAIR;
  NIL operation;
  PAIR;
}