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"