Celestin Apprentice 4/Apprentice-Release4.iso/Languages/CW MacMindy 1.4/Examples/Modules/stack.dyl

Text File | 1995-11-14 | 767 b | 35 lines | [TEXT/CWIE]

module:            Stack
author:            Patrick C. Beard <[e-mail]>
description:    A simple LIFO stack.

define module Stack
    use Dylan;                // all programs need this.
    export
        <stack>,
        top;
end module Stack;

define class <stack> (<object>)
    slot %contents :: <list>,
        init-value: #();
end class <stack>;

define method push (stack :: <stack>, value) => (stack :: <stack>);
    stack.%contents := pair(value, stack.%contents);
    stack;
end method;

define method pop (stack :: <stack>) => (value :: <object>);
    let value = top(stack);
    stack.%contents := tail(stack.%contents);
    value;
end method;

define method top (stack :: <stack>) => (value :: <object>);
    if (~empty?(stack.%contents))
        head(stack.%contents);
    else
        error("stack is empty!");
    end if;
end method;