Tim Daly on Symbolics and the elimination of the Compile-Pray-Debug Cycle:

"The Symbolics machine (its kittens all the way down...) gave me the insight that one of the most important parts of programming is the time it takes to "close the loop". Start from the point of failure, find the failure in source code, fix the failure, recompile, and re-execute. Measure the time that takes. Call this cycle the OODA loop (after the military acronym).

On a Symbolics machine, the OODA loop takes seconds. In Java it can take many minutes to an hour or more. Common lisp on stock hardware takes about a factor of 10 less than Java. Your OODA loop time may vary.

But the important point is that this OODA loop is a vital measure of how productive a language and its environment can be. By any measure, the Symbolics lisp machine was exceptional."

In On Lisp, Paul Graham likens the traditional compile/pray/debug cycle suffered by programmers to having a conversation with a friend orbiting in outer space, several light-minutes away. Whereas using a Lisp-style REPL - especially in the form it takes under Symbolics Genera - is like having a normal face-to-face conversation. This results in qualitative differences in just what kind of conversations you are able and willing to have.