# `EEVM.Interpreter.Instructions.StackMemoryStorage.StackOps`
[🔗](https://github.com/mw2000/eevm/blob/v0.1.0/lib/eevm/interpreter/instructions/stack_memory_storage/stack_ops.ex#L1)

Stack manipulation opcodes: POP (0x50), DUP1–DUP16 (0x80–0x8F), and
SWAP1–SWAP16 (0x90–0x9F).

# `stack_op`

```elixir
@spec stack_op(non_neg_integer(), [non_neg_integer()]) :: [non_neg_integer()]
```

Applies a stack manipulation opcode to the stack (a list, top first) and
returns the new stack.

- POP discards the top element.
- DUPn pushes a copy of the nth element (DUP1 copies the top).
- SWAPn exchanges the top element with the one n below it.

The interpreter has already checked that the stack holds the opcode's inputs.

    iex> alias EEVM.Interpreter.Instructions.StackMemoryStorage.StackOps
    iex> StackOps.stack_op(0x50, [1, 2])
    [2]
    iex> StackOps.stack_op(0x81, [1, 2, 3])
    [2, 1, 2, 3]
    iex> StackOps.stack_op(0x91, [1, 2, 3, 4])
    [3, 2, 1, 4]

---

*Consult [api-reference.md](api-reference.md) for complete listing*