Functional Logic Programming

Functional logic programming aims to amalgamate the most important declarative programming paradigms, namely functional programming and logic programming. In comparison with pure functional languages, functional logic languages have more expressive power due to the availability of features like function inversion, partial data structures, existential variables, and non-deterministic search. In comparison with pure logic languages, functional logic languages have a more efficient operational behavior since functions provide for more efficient evaluation strategies (lazy evaluation, deterministic reductions) than predicates. Early research in this area has been concentrated on the definition and improvement of appropriate execution principles for functional logic languages. In recent years efficient implementations of these execution principles have been developed. You can look into an older survey and a newer survey of this area.

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Languages, Implementations
Curry: a proposal for a standard in functional logic programming
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Some researchers interested in functional logic programming
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