learn rules: #=>

 #=> :
    description:
        op |ket> #=> sequence
        op |ket> #=>
            statements ... 

        associate the uncompiled sequence with op|ket>
        this "sequence" can be any type of BaseSequence
        on invocation of op|ket>, the sequence is compiled and then returned
        frequently used with label-descent

    examples:
        -- print out when invoked:
        invoke |me> #=> print |I have just been invoked!>

        -- see what we now know:
        sa: dump
            ------------------------------------------
            |context> => |Global context>

            invoke |me> #=> print|I have just been invoked!>
            ------------------------------------------

        -- now invoke it:
        sa: invoke |me>

            I have just been invoked!
            |I have just been invoked!>

    see also:
        => , .=> , +=> , !=>