Collectors is a common lisp library to help accumulate values, that I just pushed to my github account.
Sometimes you just want to collect a list of things. Actually I need to do this all the time. Usually I end up iterating over something in which case Iterate‘s collecting/appending/unioning clauses serve me well. Sometimes though, that just is not a good fit, or I need to accumulate in places iterate deems unacceptable. In these cases it is nice to have specific collector macros. These setup an environment where a function is available that when called with an argument collects it, or when called without arguments returns the results of the collection.
These macros started as a piece of arnesi, but have been modified and added to. It is also nice to be able to include a library for a specific functionality set rather than a bag of semi-related, useful things.