Dual Light Affine Logic Research Articles

Computation by interaction for space-bounded functional programming

When programming with sublinear space constraints one often needs to use special implementation techniques even for simple tasks, such as function composition. In this paper, we study how such implementation techniques can be supported in a functional programming language. Our approach is based on modelling computation by interaction using the Int construction of Joyal, Street & Verity. We apply this construction to a term model of a first-order programming language and use the resulting structure to derive the functional programming language intml. Intml can be understood as a programming language simplification of Stratified Bounded Affine Logic. We formulate intml by means of a type system inspired by Baillot & Terui's Dual Light Affine Logic. We show that it captures the complexity classes flogspace and nflogspace. We illustrate its expressiveness by showing how typical graph algorithms, such a test for acyclicity in undirected graphs, can be represented.

Light combinators for finite fields arithmetic

This work completes the definition of a library which provides the basic arithmetic operations in binary finite fields as a set of functional terms with very specific features. Such a functional terms have type in Typeable Functional Assembly (TFA). TFA is an extension of Dual Light Affine Logic (DLAL). DLAL is a type assignment designed under the prescriptions of Implicit Computational Complexity (ICC), which characterises polynomial time costing computations.We plan to exploit the functional programming patterns of the terms in the library to implement cryptographic primitives whose running-time efficiency can be obtained by means of the least hand-made tuning as possible.We propose the library as a benchmark. It fixes a kind of lower bound on the difficulty of writing potentially interesting low cost programs inside languages that can express only computations with predetermined complexity. In principle, every known and future ICC compliant programming language for polynomially costing computations should supply a simplification over the encoding of the library we present, or some set of combinators of comparable interest and difficulty.We finally report on the applicative outcome that our library has and which is a reward we get by programming in the very restrictive scenario that TFA provides. The term of TFA which encodes the inversion in binary fields suggested us a variant of a known and efficient imperative implementation of the inversion itself given by Fong. Our variant, can outperform Fong's implementation of inversion on specific hardware architectures.

A type system for PSPACE derived from light linear logic

We present a polymorphic type system for lambda calculus ensuring that well-typed programs can be executed in polynomial space: dual light affine logic with booleans (DLALB). To build DLALB we start from DLAL (which has a simple type language with a linear and an intuitionistic type arrow, as well as one modality) which characterizes FPTIME functions. In order to extend its expressiveness we add two boolean constants and a conditional constructor in the same way as with the system STAB. We show that the value of a well-typed term can be computed by an alternating machine in polynomial time, thus such a term represents a program of PSPACE (given that PSPACE = APTIME). We also prove that all polynomial space decision functions can be represented in DLALB. Therefore DLALB characterizes PSPACE predicates.

Light types for polynomial time computation in lambda calculus

We present a polymorphic type system for lambda calculus ensuring that well-typed programs can be executed in polynomial time: dual light affine logic (DLAL). DLAL has a simple type language with a linear and an intuitionistic type arrow, and one modality. It corresponds to a fragment of light affine logic (LAL). We show that contrarily to LAL, DLAL ensures good properties on lambda-terms (and not only on proof-nets): subject reduction is satisfied and a well-typed term admits a polynomial bound on the length of any of its beta reduction sequences. We also give a translation of LAL into DLAL and deduce from it that all polynomial time functions can be represented in DLAL.

Verification of Ptime Reducibility for system F Terms: Type Inference in Dual Light Affine Logic

In a previous work Baillot and Terui introduced Dual light affine logic (DLAL) as a variant of Light linear logic suitable for guaranteeing complexity properties on lambda calculus terms: all typable terms can be evaluated in polynomial time by beta reduction and all Ptime functions can be represented. In the present work we address the problem of typing lambda-terms in second-order DLAL. For that we give a procedure which, starting with a term typed in system F, determines whether it is typable in DLAL and outputs a concrete typing if there exists any. We show that our procedure can be run in time polynomial in the size of the original Church typed system F term.