# RE: [stack] Reversible computation and Joy

## wtanksley@bigfoot.com — 2000-05-15 17:20:27

    From: srenner@... [mailto:srenner@...]

     >If Joy is understood as linear (currently a topic of debate here),

     It undeniably can be made so, if it isn't already.

     >then is a Joy computation reversible? My intuition is that Joy can be

    >made reversible if  "garbage" is not collected during a computation

    >but pushed onto a "garbage stack".

    >[2 2 +] i == 4

    >3 1 + == 4

    >2 sq == 4

    >123 121 - == 4

    >Given 4 on the stack, what information do we need to reconstruct the

    >computation that created it? Isn't this information exactly the same

    >as the "garbage" we would normally collect?

     I don't think so -- I think you'd need to have (for example) + return both

    the answer and one of the addends.  So

      [2 2 +] i == 4 [2 2 +]  ( ? )

      3 1 + == 1 4

      2 sq == 4

      123 121 - == 121 4

    I'm not sure about how to handle the quotation unwrapping, honestly.

    -Billy