A compiler plugin to add a new phase to the compiler which supports mutual tail recursion. TwoTails adds in a code transforming phase to the compiler. As such, code using macros or code enhancing techniques (such as that in Spring) may fail to compile at best or work in an unexpected manner at worst. We want to specifically call out AoP libraries such as AspectJ where the intention of an author is to have each "loop" of the recursive call trigger some side-effect. In such cases, similar to code using @tailcall, only the first "loop" will induce the effect; all others will have been compiled away.