Liberal Typing for Functional Logic Programs

López-Fraguas, Francisco Javier; Martin-Martin, Enrique; Rodríguez-Hortalá, Juan

doi:10.1007/978-3-642-17164-2_7

Cited by 5 publications

(9 citation statements)

References 24 publications

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“…This contrasts with [15], where we proposed another type system that breaks parametricity even further. In that work the instantiation of polymorphic type variables is allowed to be performed not only in opaque patterns but in any pattern of the program.…”

Section: Parametricitymentioning

confidence: 82%

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Safe typing of functional logic programs with opaque patterns and local bindings

López-Fraguas

Martin-Martin

Rodríguez-Hortalá

2014

Information and Computation

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Type systems are widely used in programming languages as a powerful tool providing safety to programs. Functional logic languages have inherited Damas-Milner type system from their functional part due to its simplicity and popularity. In this paper we address a couple of aspects that can be subject of improvement. One is related to a problematic feature of functional logic languages not taken under consideration by standard systems: it is known that the use of opaque HO patterns in left-hand sides of program rules may produce undesirable effects from the point of view of types. We reexamine the problem, and propose two variants of a Damas-Milner-like type system where certain uses of HO patterns (even opaque) are permitted while preserving type safety. The considered formal framework is that of programs without extra variables and using let-rewriting as reduction mechanism. The other aspect addressed is the different ways in which polymorphism of local definitions can be handled. At the same time that we formalize the type system, we have made the effort of technically clarifying the overall process of type inference in a whole program.

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Section: Parametricitymentioning

confidence: 82%

“…This makes a big difference with another recent work [15] where we develop a type system that deliberately aims to go beyond Damas-Milner types by radically liberalizing the well-typedness conditions for FLP programs.…”

Section: Higher Order Patternsmentioning

confidence: 99%

Safe typing of functional logic programs with opaque patterns and local bindings

López-Fraguas

Martin-Martin

Rodríguez-Hortalá

2014

Information and Computation

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“…In this way, the formalisms are relatively close and moving from one to another becomes technically more natural and comfortable. This applies also to some further developments of our setting that we have made so far, like the extension to higher order features given in (López-Fraguas et al 2008), the combination of semantics proposed in (López-Fraguas et al 2009a), or the application of let-rewriting as underlying formal notion of reduction for type systems in functional logic languages (López-Fraguas et al 2010b;López-Fraguas et al 2010a).…”

Section: Introductionmentioning

confidence: 87%

Rewriting and narrowing for constructor systems with call-time choice semantics

López-Fraguas¹,

Martin-Martin²,

Rodríguez-Hortalá³

et al. 2012

Theory and Practice of Logic Programming

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Non-confluent and non-terminating {constructor-based term rewriting systems are useful for the purpose of specification and programming. In particular, existing functional logic languages use such kinds of rewrite systems to define possibly non-strict non-deterministic functions. The semantics adopted for non-determinism is call-time choice, whose combination with non-strictness is a non-trivial issue, addressed years ago from a semantic point of view with the Constructor-based Rewriting Logic (CRWL), a well-known semantic framework commonly accepted as suitable semantic basis of modern functional logic languages. A drawback of CRWL is that it does not come with a proper notion of one-step reduction, which would be very useful to understand and reason about how computations proceed. In this paper, we develop thoroughly the theory for the first-order version of let-rewriting, a simple reduction notion close to that of classical term rewriting, but extended with a let-binding construction to adequately express the combination of call-time choice with non-strict semantics. Let-rewriting can be seen as a particular textual presentation of term graph rewriting. We investigate the properties of let-rewriting, most remarkably their equivalence with respect to a conservative extension of the CRWL-semantics coping with let-bindings, and we show by some case studies that having two interchangeable formal views (reduction/semantics) of the same language is a powerful reasoning tool. After that, we provide a notion of let-narrowing, which is adequate for call-time choice as proved by soundness and completeness results of let-narrowing with respect to let-rewriting. Moreover, we relate those let-rewriting and let-narrowing relations (and hence CRWL) with ordinary term rewriting and narrowing, providing in particular soundness and completeness of let-rewriting with respect to term rewriting for a class of programs which are deterministic in a semantic sense.

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“…The program contains an overloaded function arb which is a nondeterministic generator, and its instance for booleans. It also contains a function arbL2 which returns a list of two elements of the In this paper we propose and evaluate a type-passing translation of type classes for FLP based on type-indexed functionsfunctions with a different behavior for different types [14]-and type witnesses-representations of types as data values-that is well-typed in a new liberal type system recently proposed for FLP [20]. The proposed translation is not integrated in the type checking phase as in [10,30], but it is a separated phase after type checking.…”

Section: Introductionmentioning

confidence: 99%

“…3. Although the broad idea of using such kind of translation is not a novelty [29], its concrete realization and the application to FLP, relying in a new type system [20], are new.…”

Section: Introductionmentioning

confidence: 99%

Type classes in functional logic programming

Martin-Martin

2011

Proceedings of the 20th ACM SIGPLAN Workshop on Partial Evaluation and Program Manipulation

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Type classes provide a clean, modular and elegant way of writing overloaded functions. Functional logic programming languages (FLP in short) like Toy or Curry have adopted the Damas-Milner type system, so it seems natural to adopt also type classes in FLP. However, type classes has been barely introduced in FLP. A reason for this lack of success is that the usual translation of type classes using dictionaries presents some problems in FLP like the absence of expected answers due to a bad interaction of dictionaries with the call-time choice semantics for non-determinism adopted in FLP systems.In this paper we present a type-passing translation of type classes based on type-indexed functions and type witnesses that is well-typed with respect to a new liberal type system recently proposed for FLP. We argue the suitability of this translation for FLP because it improves the dictionary-based one in three aspects. First, it obtains programs which run as fast or faster-with an speedup from 1.05 to 2.30 in our experiments. Second, it solves the mentioned problem of missing answers. Finally, the proposed translation generates shorter and simpler programs.

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Liberal Typing for Functional Logic Programs

Cited by 5 publications

References 24 publications

Safe typing of functional logic programs with opaque patterns and local bindings

Safe typing of functional logic programs with opaque patterns and local bindings

Rewriting and narrowing for constructor systems with call-time choice semantics

Type classes in functional logic programming

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