simpliest michelson example

gistfile1.txt

# This contract contains an integer in the storage (= a counter).
# It has two entrypoints :
#  - increaseCounterBy : storage = storage + value
#  - decreaseCounterBy : storage = storage - value
parameter (or (int %increaseCounterBy) (int %decreaseCounterBy));
storage int;
code {
      UNPAIR;
      IF_LEFT {
                ADD
              }
              {
                SWAP;
                SUB
              };
      NIL operation;
      PAIR;
    }