Polish expression: 13, 4, -, 2, 3, *, +

stack count:  7     kind: value        val: 13
stack count:  6     kind: value        val:  4
stack count:  5     kind: operator      op:  -
stack count:  4     kind: value        val:  2
stack count:  3     kind: value        val:  3
stack count:  2     kind: operator      op:  *
stack count:  1     kind: operator      op:  +
stack count:  0

Polish evaluation: 15