[1 2 3]:a; # numeric only array, assigned to a and then dropped
10,:a;     # assign to a [0 1 2 3 4 5 6 7 8 9]
a 0= puts  # pick element at index 0 (stack: 0)
a 10+puts  # append 10 to the end of a
10 a+puts  # prepend 10 to a