Abstract. Functional logic programming languages combine the most important declarative programming paradigms, and attempts to combine these paradigms have a long history. The declarative multi-paradigm language Curry is influenced by recent advances in the foundations and implementation of functional logic languages. The development of Curry is an international initiative intended to provide a common platform for the research, teaching, and application of integrated functional logic languages. This paper surveys the foundations of functional logic programming that are relevant for Curry, the main features of Curry, and extensions and applications of Curry and functional logic programming. 1

In this paper we propose a new approach to implement web services based on the Common Gateway Interface (CGI). Since we use the multi-paradigm declarative language Curry as an implementation language, many of the drawbacks and pitfalls of traditional CGI programming can be avoided. For instance, the syntactical details of HTML and passing values with CGI are hidden by a wrapper that executes abstract HTML forms by translating them into concrete HTML code. This leads to a high-level approach to server side web service programming where notions like event handlers, state variables and control of interactions are available. Thanks to the use of a functional logic language, we can structure our approach as an embedded domain specic language where the functional and logic programming features of the host language are exploited to abstract from details and frequent errors in standard CGI programming.

Abstract. We introduce a handful of software design patterns for functional logic languages. Following usual approaches, for each pattern we propose a name and we describe its intent, applicability, structure, consequences, etc. Our patterns deal with data type construction, identifier declarations, mappings, search, nondeterminism and other fundamental aspects of the design and implementation of programs. We present some problems and we show fragments of programs that solve these problems using our patterns. The programming language of our examples is Curry. The complete programs are available on-line. 1

Partial evaluation is an automatic technique for program optimization which preserves program semantics. The range of its potential applications is extremely large, as witnessed by successful experiences in several fields. This paper summarizes our findings in the development of partial evaluation tools for Curry, a modern multi-paradigm declarative language which combines features from functional, logic and concurrent programming. From a practical point of view, the most promising approach appears to be a recent partial evaluation framework which translates source programs into a maximally simplified representation. We support this statement by extending the underlying method in order to design a practical partial evaluation tool for the language Curry. The process is fully automatic and can be incorporated into a Curry compiler as a source-to-source transformation on intermediate programs. An implementation of the partial evaluator has been undertaken. Experimental resul...

In this paper we propose a new concept to deal with dynamic predicates in functional logic programs. The definition of a dynamic predicate can change over time, i.e., one can add or remove facts that define this predicate. Our approach is easy to use and has a clear semantics that does not depend on the particular (demand-driven) evaluation strategy of the underlying implementation. In particular, the concept is not based on (unsafe) side effects so that the order of evaluation does not influence the computed results—an essential requirement in non-strict languages. Dynamic predicates can also be persistent so that their definitions are saved across invocations of programs. Thus, dynamic predicates are a lightweight alternative to the explicit use of external database systems. Moreover, they extend one of the classical application areas of logic programming to functional logic programs. We present the concept, its use and an implementation in a Prolog-based compiler. 1 Motivation and Related Work Functional logic languages [11] aim to integrate the best features of functional and logic languages in order to provide a variety of programming concepts to the programmer. For instance, the concepts of demand-driven evaluation, higherorder functions, and polymorphic typing from functional programming can be combined with logic programming features like computing with partial information (logical variables), constraint solving, and non-deterministic search for solutions. This combination leads to optimal evaluation strategies [2] and new design patterns [4] that can be applied to provide better programming abstractions, e.g., for implementing graphical user interfaces [13] or programming dynamic web pages [14]. However, one of the traditional application areas of logic programming is not yet sufficiently covered in existing functional logic languages: the combination

The aim of many program transformers is to improve efficiency while preserving program meaning. Correctness issues have been dealt with extensively. However, very little attention has been paid to formally establish the improvements achieved by these transformers. In this work, we introduce the scheme of a narrowing-driven partial evaluator enhanced with abstract costs. They are "abstract" in the sense that they measure the number of basic operations performed during a computation rather than actual execution times. Thus, we have available a setting in which one can discuss the effects of the program transformer in a precise framework and, moreover, to quantify these effects. Our scheme may serve as a basis to develop speedup analyses and cost-guided transformers. An implementation of the cost-augmented specializer has been undertaken, which demonstrates the practicality of our approach.

This paper presents an environment to support high-level database programming in the multi-paradigm declarative programming language Curry. We define an application programming interface (API) that abstracts from the concrete database access methods. The API supports transactions and exploits Curry’s type system to ensure a strict separation between queries and updates. In order to ensure database updates that are safe w.r.t. an intended data model (e.g., containing specific relations between entities), we assume a description of the data dependencies in the entity-relationship (ER) model from which all access and update operations related to the database are generated. We propose a representation of ER diagrams in the declarative language Curry so that they can be constructed by various tools and then translated into this representation. Furthermore, we have implemented a compiler from this representation into a Curry program that provides safe access and update operations based on the API for database programming.

In this paper we present CIDER (Curry Integrated Development EnviRonment), an analysis and programming environment for the declarative multi-paradigm language Curry. CIDER is a graphical environment to support the development of Curry programs by providing integrated tools for the analysis and visualization of programs. CIDER is completely implemented in Curry using libraries for GUI programming (based on Tcl/Tk) and meta-programming. An important aspect of our environment is the possible adaptation of the development environment to other declarative source languages (e.g., Prolog or Haskell) and the extensibility w.r.t. new analysis methods. To support the latter feature, the lazy evaluation strategy of the underlying implementation language Curry becomes quite useful.

Functional logic languages combine nondeterministic search facilities of logic languages with features of functional languages, e.g., monadic I/O to provide a declarative method to deal with I/O actions. Unfortunately, monadic I/O cannot be used in programs which split the computation due to nondeterministic reductions. This problem can be avoided if nondeterministic computations are encapsulated by search operators which are available, for instance, in the multi-paradigm language Curry. To support the programmer in identifying nondeterministic parts of a program, we develop a method based on a type and eect system that will nd every possible source of nondeterminism. Additionally, such information can be exploited in compilers to optimize deterministically reducible parts of a program.

Bernd Brael , Michael Hanus , and Frank Steiner RWTH Aachen, Germany brassel@halifax.rwth-aachen.de Institut fur Informatik, CAU Kiel, D-24098 Kiel, Germany fmh,fstg@informatik.uni-kiel.de Abstract. While declarative programming languages are based on the idea of specifying the static relationships of problems, the right modeling of the dynamic behavior is equally important for many practical applications.