2 research outputs found
A Logic Programming Playground for Lambda Terms, Combinators, Types and Tree-based Arithmetic Computations
With sound unification, Definite Clause Grammars and compact expression of
combinatorial generation algorithms, logic programming is shown to conveniently
host a declarative playground where interesting properties and behaviors emerge
from the interaction of heterogenous but deeply connected computational
objects.
Compact combinatorial generation algorithms are given for several families of
lambda terms, including open, closed, simply typed and linear terms as well as
type inference and normal order reduction algorithms. We describe a
Prolog-based combined lambda term generator and type-inferrer for closed
well-typed terms of a given size, in de Bruijn notation.
We introduce a compressed de Bruijn representation of lambda terms and define
its bijections to standard representations. Our compressed terms facilitate
derivation of size-proportionate ranking and unranking algorithms of lambda
terms and their inferred simple types.
The S and K combinator expressions form a well-known Turing-complete subset
of the lambda calculus. We specify evaluation, type inference and combinatorial
generation algorithms for SK-combinator trees. In the process, we unravel
properties shedding new light on interesting aspects of their structure and
distribution.
A uniform representation, as binary trees with empty leaves, is given to
expressions built with Rosser's X-combinator, natural numbers, lambda terms and
simple types. Using this shared representation, ranking/unranking algorithm of
lambda terms to tree-based natural numbers are described.
Our algorithms, expressed as an incrementally developed literate Prolog
program, implement a declarative playground for exploration of representations,
encodings and computations with uniformly represented lambda terms, types,
combinators and tree-based arithmetic.Comment: 70 page
Formula Transformers and Combinatorial Test Generators for Propositional Intuitionistic Theorem Provers
We develop combinatorial test generation algorithms for progressively more
powerful theorem provers, covering formula languages ranging from the
implicational fragment of intuitionistic logic to full intuitionistic
propositional logic. Our algorithms support exhaustive and random generators
for formulas of these logics.
To provide known-to-be-provable formulas, via the Curry-Howard
formulas-as-types correspondence, we use generators for typable lambda terms
and combinator expressions. Besides generators for several classes of formulas,
we design algorithms that restrict formula generation to canonical
representatives among equiprovable formulas and introduce program
transformations that reduce formulas to equivalent formulas of a simpler
structure. The same transformations, when applied in reverse, create harder
formulas that can catch soundness or incompleteness bugs.
To test the effectiveness of the testing framework itself, we describe use
cases for deriving lightweight theorem provers for several of these logics and
for finding bugs in known theorem provers. Our Prolog implementation available
at: https://github.com/ptarau/TypesAndProofs and a subset of formula generators
and theorem provers, implemented in Python is available at:
https://github.com/ptarau/PythonProvers.
Keywords: term and formula generation algorithms, Prolog-based theorem
provers, formulas-as-types, type inference and type inhabitation, combinatorial
testing, finding bugs in theorem provers.Comment: 32 page