Parsing with derivatives may be viewed as a form of breadth-first recursive descent. Breadth-first search is orthogonal to depth-first search, and two lines which are orthogonal in two-dimensional Euclidean space may also be said to be perpendicular. Thus, an appropriate name for this library might be "parsper", as a shortening of "parse perpendicular". Such a name is eminently googleable and implies a wealth of potential Star Trek puns. Unfortunately, it looks far too much like a typo. Thus, "parseback" serves both as a faux shortening of "parse backwards" and a reference to "logback", for no particular reason. Parseback is a Scala implementation of parsing with derivatives (Might, Darais, Spiewak; 2011) taking into account the significant refinements of described by Adams, Hollenbeck and Might. It is designed to be an idiomatic, convenient and safe parser combinator library for formal general context-free grammars with production-viable performance.