  Most functional languages rely on some garbage collection for automatic
memory management. They usually eschew reference counting in favor of a tracing
garbage collector, which has less bookkeeping overhead at runtime. On the other
hand, having an exact reference count of each value can enable optimizations,
such as destructive updates. We explore these optimization opportunities in the
context of an eager, purely functional programming language. We propose a new
mechanism for efficiently reclaiming memory used by nonshared values, reducing
stress on the global memory allocator. We describe an approach for minimizing
the number of reference counts updates using borrowed references and a
heuristic for automatically inferring borrow annotations. We implemented all
these techniques in a new compiler for an eager and purely functional
programming language with support for multi-threading. Our preliminary
experimental results demonstrate our approach is competitive and often
outperforms state-of-the-art compilers.
