Chapters:
1: Introduction
2: Simple example
3: Invocation
4: Finer Control
5: X-Y Plots
6: Contour Plots
7: Image Plots
8: Examples
9: Gri Commands
10: Programming
11: Environment
12: Emacs Mode
13: History
14: Installation
15: Gri Bugs
16: Test Suite
17: Gri in Press
18: Acknowledgments
19: License
Indices:
Concepts
Commands
Variables

### 10.9.1: Stack Operators

Stack operators manipulate or display the stack.

``pop`' removes the top item from the stack (see Unary Operators).

``dup`' duplicates the top item on the stack (see Unary Operators).

``exch`' reorders the top two items on the stack (see Binary Operators).

``pstack`' prints the items on the stack (without changing the stack).

``roll_right`' rolls the items to the right.

``roll_left`' rolls the items to the left.

For example, the following shows how you might use ``exch`' or ``roll_right`' to change the sense of a subtraction.

    show {rpn 1 2            -} " ... yields -1"
    show {rpn 1 2 exch       -} " ... yields  1"
    show {rpn 1 2 roll_right -} " ... yields  1"