Functional and Constraint Logic Programming

Abstract
This volume contains the proceedings of the 20th International Workshop onFunctional and (Constraint) Logic Programming (WFLP 2011), held in Odense,Denmark, July 19, 2011 at the University of Southern Denmark. WFLP aims atbringing together researchers interested in functional programming, (constraint)logic programming, as well as the integration of the two paradigms. It promotesthe cross-fertilizing exchange of ideas and experiences among researchers andstudents from the different communities interested in the foundations, applicationsand combinations of high-level, declarative programming languages andrelated areas. The previous editions of this workshop were:WFLP 2010 (Madrid,Spain), WFLP 2009 (Brasilia, Brazil), WFLP 2008 (Siena, Italy), WFLP 2007(Paris, France), WFLP 2006 (Madrid, Spain), WCFLP 2005 (Tallinn, Estonia),WFLP 2004 (Aachen, Germany), WFLP 2003 (Valencia, Spain), WFLP 2002(Grado, Italy), WFLP 2001 (Kiel, Germany), WFLP 2000 (Benicassim, Spain),WFLP 1999 (Grenoble, France), WFLP 1998 (Bad Honnef, Germany), WFLP1997 (Schwarzenberg,Germany),WFLP 1996 (Marburg, Germany),WFLP 1995(Schwarzenberg, Germany), WFLP 1994 (Schwarzenberg, Germany), WFLP1993 (Rattenberg, Germany), and WFLP 1992 (Karlsruhe, Germany). Since its2009 edition, the WFLP proceedings have been published by Springer in its LectureNotes in Computer Science series, as volumes 5979 and 6559, respectively.Each submission of WFLP 2011 was peer-reviewed by at least three ProgramCommittee members with the help of some external experts. The Program Committeemeeting was conducted electronically in May 2011 with the help of theconference management system EasyChair. After careful discussions, the ProgramCommittee selected ten submissions for presentation at the workshop. Nineof them were considered mature enough to be published in these proceedings.On behalf of the Program Committee, I would like to thank all researchers,who gave talks at the workshop, contributed to the proceedings, and submittedpapers to WFLP 2011. As Program Chair, I would also like to thank all membersof the Program Committee and the external reviewers for their careful work.Moreover, I am pleased to acknowledge the valuable assistance of the conferencemanagement system EasyChair and to thank its developer Andrei Voronkov forproviding it. Finally, all the participants ofWFLP 2011 and I are deeply indebtedto Peter Schneider-Kamp and his team, who organized the Odense Summer onLogic and Programming, which besides WFLP comprised the 21st InternationalSymposium on Logic-Based Program Synthesis and Transformation (LOPSTR2011), the 13th International ACM SIGPLAN Symposium on Principles andPractice of Declarative Programming (PPDP 2011), and the 4th InternationalWorkshop on Approaches and Applications of Inductive Programming (AAIP2011). All the local organizers did a wonderful job and provided invaluable supportin the preparation and organization of the overall event.

Keywords
functional logic programming; functional programming; constraint logic programming; declarative programming; integration of programming paradigms; term rewriting