=Paper=
{{Paper
|id=Vol-1335/wflp2014_tutorial
|storemode=property
|title=Declarative Multi-paradigm Programming
|pdfUrl=https://ceur-ws.org/Vol-1335/wflp2014_tutorial.pdf
|volume=Vol-1335
|dblpUrl=https://dblp.org/rec/conf/wlp/Hanus14
}}
==Declarative Multi-paradigm Programming==
https://ceur-ws.org/Vol-1335/wflp2014_tutorial.pdf
Declarative Multi-paradigm Programming
Michael Hanus
Institut für Informatik, CAU Kiel, D-24098 Kiel, Germany.
mh@informatik.uni-kiel.de
Abstract. This tutorial provides an overview and introduction to
declarative programming exploiting multiple paradigms, in particular,
functional, logic, and constraint programming. To demonstrate the pos-
sibility to support these paradigms within a single programming model,
we survey the features of the declarative multi-paradigm language Curry.
1 Overview
Compared to traditional imperative languages, declarative programming lan-
guages provide a higher and more abstract level of programming that leads to
reliable and maintainable programs. However, there is no distinct “declarative
programming” paradigm. Instead, there are various programming paradigms and
related languages based on different methods to structure declarative knowledge.
Functional programming is based on the lambda calculus and provide functions
as computational entities. Logic programming is based on first-order predicate
logic and uses predicates as basic programming entities. Constraint program-
ming offers constraint solvers to reason about models described with the help
of various constraint structures. Although the motivation to exploit high-level
programming is similar in all paradigms, the concrete languages associated to
them are quite different. Thus, it is a natural idea to combine these worlds of
programming into a single paradigm, and attempts for doing so have a long
history. However, the interactions between functional and logic programming
features are complex in detail so that the concrete design of such declarative
multi-paradigm languages is a non-trivial task. This is demonstrated by a lot of
research work on the semantics, operational principles, and implementation of
functional logic languages since more than two decades. Fortunately, recent ad-
vances in the foundation and implementation of functional logic languages have
shown reasonable principles that lead to the design of practically applicable
programming languages.
This tutorial provides an overview on the principles of integrated functional
logic languages. As a concrete programming language, we survey the declarative
multi-paradigm language Curry1 [13, 20]. It is developed by an international
initiative of researchers in this area and intended to provide a common platform
for research, teaching, and application of integrated functional logic languages.
1
http://www.curry-language.org
Details about functional logic programming and Curry can be found in recent
surveys [5, 18] and in the language report [20].
The integration of functional and logic programming has various advantages.
Beyond the fact that one can use the best features of declarative languages
in a single language, like strong typing, higher-order functions, optimal (lazy)
evaluation from functional programming, or non-determinism, computing with
partial information, and constraint solving from logic programming, there are
also clear advantages compared to the individual paradigms. For instance, the
combination of lazy evaluation and non-determinism leads to a demand-driven
exploration of the search space which is sometimes more efficient and optimal
for particular classes of programs [2]. Moreover, non-declarative features, which
are regularly used in practical logic programs, can be avoided in functional logic
languages, e.g., by functional notation or declarative I/O [22].
The combined features offered by functional logic languages led to new design
patterns [3, 6], better abstractions for application programming (e.g., program-
ming with databases [7, 11], GUI programming [14], web programming [15, 16,
19], string parsing [10]), and new techniques to implement programming tools,
like partial evaluators [1] or test case generators [12, 21]. In particular, functional
patterns, as proposed in [4], exploit non-determinism from logic programming
and demand-driven pattern matching from functional programming in order
to achieve a powerful executable specification method. For instance, functional
patterns have been used for XML processing [17] where it has been shown that
specialized logic programming approaches [8, 9] can be implemented with a few
lines of code in Curry. Some of these techniques are reviewed in this tutorial.
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