Discussions on functional programming often revolve around the virtues of higher-order functions, algebraic data types, type classes, and various other well-established modularity techniques. From an architectural perspective, however, these techniques play a secondary role relative to the ultimate goal of functional programming: quoting Prof. Wadler, “A functional programming language is a domain-specific language for implementing domain-specific languages.” The purpose of this talk is to emphasize the architectural significance of DSLs in functional applications and to illustrate this concept using the tagless-final style.