Kleisli is a modern data integration system that has made a significant impact on bioinformatics data integration. The primary query language provided by Kleisli is called CPL, which is a functional query language whose surface syntax is based on the comprehension syntax. Kleisli is itself implemented using the functional language SML. This paper describes the influence of functional programming research that benefits the Kleisli system, especially the less obvious ones at the implementation level. 1 Introduction The Kleisli system [14] is an advanced broad-scale integration technology that has proved useful in the bioinformatics arena. Many bioinformatics problems require access to data sources that are high in volume, highly heterogeneous and complex, constantly evolving, and geographically dispersed. Solutions to these problems usually involve multiple carefully sequenced steps and require information to be passed smoothly between the steps. Kleisli is designed to handle these req...