foreplay is a set of MAX/MSP externals for genetic mutation of one to four integers. They follow a concept I call subjective evolution (SE). As in the Dawkins' example, after comparing each mutation of the parent (in this case by listening) the user chooses which child is the most fit. This child is then made the parent of the next generation, hence subjective evolution.
The set consists of foreplay1, foreplay2, foreplay3 and foreplay4. The file's suffix indicates how may inputs/outputs it has. Below is an image of the help file for foreplay4 so you can see how it works.

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If you'd like the C source e-mail me.