[mcartyem]

I can see how closures would take some work. Thanks.

There's evidence garbage collection was not the desired solution but a plan B. McCarthy writes the reason reference counting was not implemented was a hardware limitation [1]:

"Since there were only six bits left in a word, and these were in separated parts of the word, reference counts seemed infeasible without a drastic change in the way list structures were represented. (A list handling scheme using reference counts was later used by Collins (1960) on a 48 bit CDC computer).

The second alternative is garbage collection..."

[1] - http://www-formal.stanford.edu/jmc/history/lisp/node3.html#S...