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Polymorphism and Separation in Hoare Type Theory
, 2006
"... In previous work, we proposed a Hoare Type Theory (HTT) which combines effectful higherorder functions, dependent types and Hoare Logic specifications into a unified framework. However, the framework did not support polymorphism, and failed to provide a modular treatment of state in specifications. ..."
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Cited by 81 (13 self)
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In previous work, we proposed a Hoare Type Theory (HTT) which combines effectful higherorder functions, dependent types and Hoare Logic specifications into a unified framework. However, the framework did not support polymorphism, and failed to provide a modular treatment of state in specifications. In this paper, we address these shortcomings by showing that the addition of polymorphism alone is sufficient for capturing modular state specifications in the style of Separation Logic. Furthermore, we argue that polymorphism is an essential ingredient of the extension, as the treatment of higherorder functions requires operations not encodable via the spatial connectives of Separation Logic.
Generic programming within dependently typed programming
 In Generic Programming, 2003. Proceedings of the IFIP TC2 Working Conference on Generic Programming, Schloss Dagstuhl
, 2003
"... Abstract We show how higher kinded generic programming can be represented faithfully within a dependently typed programming system. This development has been implemented using the Oleg system. The present work can be seen as evidence for our thesis that extensions of type systems can be done by prog ..."
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Cited by 66 (8 self)
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Abstract We show how higher kinded generic programming can be represented faithfully within a dependently typed programming system. This development has been implemented using the Oleg system. The present work can be seen as evidence for our thesis that extensions of type systems can be done by programming within a dependently typed language, using data as codes for types. 1.
TypeBased Termination of Recursive Definitions
, 2002
"... This article The purpose of this paper is to introduce b, a simply typed calculus that supports typebased recursive definitions. Although heavily inspired from previous work by Giménez (Giménez 1998) and closely related to recent work by Amadio and Coupet (Amadio and CoupetGrimal 1998), the techn ..."
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Cited by 52 (4 self)
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This article The purpose of this paper is to introduce b, a simply typed calculus that supports typebased recursive definitions. Although heavily inspired from previous work by Giménez (Giménez 1998) and closely related to recent work by Amadio and Coupet (Amadio and CoupetGrimal 1998), the technical machinery behind our system puts a slightly different emphasis on the interpretation of types. More precisely, we formalize the notion of typebased termination using a restricted form of type dependency (a.k.a. indexed types), as popularized by (Xi and Pfenning 1998; Xi and Pfenning 1999). This leads to a simple and intuitive system which is robust under several extensions, such as mutually inductive datatypes and mutually recursive function definitions; however, such extensions are not treated in the paper
Abstract predicates and mutable ADTs in Hoare type theory
 IN PROC. ESOP’07, VOLUME 4421 OF LNCS
, 2007
"... Hoare Type Theory (HTT) combines a dependently typed, higherorder language with monadically encapsulated, stateful computations. The type system incorporates pre and postconditions, in a fashion similar to Hoare and Separation Logic, so that programmers can modularly specify the requirements and ..."
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Cited by 50 (21 self)
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Hoare Type Theory (HTT) combines a dependently typed, higherorder language with monadically encapsulated, stateful computations. The type system incorporates pre and postconditions, in a fashion similar to Hoare and Separation Logic, so that programmers can modularly specify the requirements and effects of computations within types. This paper extends HTT with quantification over abstract predicates (i.e., higherorder logic), thus embedding into HTT the Extended Calculus of Constructions. When combined with the Hoarelike specifications, abstract predicates provide a powerful way to define and encapsulate the invariants of private state; that is, state which may be shared by several functions, but is not accessible to their clients. We demonstrate this power by sketching a number of abstract data types and functions that demand ownership of mutable memory, including an idealized custom memory manager.
Elimination with a Motive.
 Types for Proofs and Programs (Proceedings of the International Workshop, TYPES’00),
, 2002
"... Abstract. I present a tactic, BasicElim, for Type Theory based proof systems to apply elimination rules in a re nement setting. Applicable rules are parametric in their conclusion, expressing the leverage hypothesesx yield on any x we choose. represents the motive for an elimination: BasicElim&apos ..."
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Cited by 48 (14 self)
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Abstract. I present a tactic, BasicElim, for Type Theory based proof systems to apply elimination rules in a re nement setting. Applicable rules are parametric in their conclusion, expressing the leverage hypothesesx yield on any x we choose. represents the motive for an elimination: BasicElim's job is to construct a suited to the goal at hand. If thesex inhabit an instance of 's domain, I adopt a technique standard in`folklore', generalizing thex and expressing the restriction by equation. A novel notion of = readily permits dependent equations, and a second tactic, Unify, simpi es the equational hypotheses thus appearing in subgoals. Given such technology, it becomes e ective to express properties of datatypes, relations and functions in this style. A small extension couples BasicElim with rewriting, allowing complex techniques to be packaged in a single rule.
Observational Equality, Now!
 A SUBMISSION TO PLPV 2007
, 2007
"... This paper has something new and positive to say about propositional equality in programming and proof systems based on the CurryHoward correspondence between propositions and types. We have found a way to present a propositional equality type • which is substitutive, allowing us to reason by repla ..."
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Cited by 43 (15 self)
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This paper has something new and positive to say about propositional equality in programming and proof systems based on the CurryHoward correspondence between propositions and types. We have found a way to present a propositional equality type • which is substitutive, allowing us to reason by replacing equal for equal in propositions; • which reflects the observable behaviour of values rather than their construction: in particular, we have extensionality— functions are equal if they take equal inputs to equal outputs; • which retains strong normalisation, decidable typechecking and canonicity—the property that closed normal forms inhabiting datatypes have canonical constructors; • which allows inductive data structures to be expressed in terms of a standard characterisation of wellfounded trees; • which is presented syntactically—you can implement it directly, and we are doing so—this approach stands at the core of Epigram 2; • which you can play with now: we have simulated our system by a shallow embedding in Agda 2, shipping as part of the standard examples package for that system [20]. Until now, it has always been necessary to sacrifice some of these aspects. The closest attempt in the literature is Altenkirch’s construction of a setoidmodel for a system with canonicity and extensionality on top of an intensional type theory with proofirrelevant propositions [4]. Our new proposal simplifies Altenkirch’s construction by adopting McBride’s heterogeneous approach to equality [18].
The derivative of a regular type is its type of onehole contexts (extended abstract), 2001. Unpublished manuscript, available via http://strictlypositive.org/diff.pdf. Conor McBride and Ross Paterson. Applicative programming with effects
"... Polymorphic regular types are treelike datatypes generated by polynomial type expressions over a set of free variables and closed under least fixed point. The ‘equality types ’ of Core ML can be expressed in this form. Given such a type expression with free, this paper shows a way to represent the ..."
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Cited by 42 (8 self)
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Polymorphic regular types are treelike datatypes generated by polynomial type expressions over a set of free variables and closed under least fixed point. The ‘equality types ’ of Core ML can be expressed in this form. Given such a type expression with free, this paper shows a way to represent the onehole contexts for elements of within elements of, together with an operation which will plug an element of into the hole of such a context. Onehole contexts are given as inhabitants of a regular type, computed generically from the syntactic structure of by a mechanism better known as partial differentiation. The relevant notion of containment is shown to be appropriately characterized in terms of derivatives and plugging in. The technology is then exploited to give the onehole contexts for subelements of recursive types in a manner similar to Huet’s ‘zippers’[Hue97]. 1
A Coverage Checking Algorithm for LF
, 2003
"... Coverage checking is the problem of deciding whether any closed term of a given type is an instance of at least one of a given set of patterns. It can be used to verify if a function defined by pattern matching covers all possible cases. This problem has a straightforward solution for the first ..."
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Cited by 38 (10 self)
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Coverage checking is the problem of deciding whether any closed term of a given type is an instance of at least one of a given set of patterns. It can be used to verify if a function defined by pattern matching covers all possible cases. This problem has a straightforward solution for the firstorder, simplytyped case, but is in general undecidable in the presence of dependent types. In this paper we present a terminating algorithm for verifying coverage of higherorder, dependently typed patterns.
Faking It: Simulating Dependent Types in Haskell
, 2001
"... Dependent types reflect the fact that validity of data is often a relative notion by allowing prior data to affect the types of subsequent data. Not only does this make for a precise type system, but also a highly generic one: both the type and the program for each instance of a family of operations ..."
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Cited by 37 (6 self)
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Dependent types reflect the fact that validity of data is often a relative notion by allowing prior data to affect the types of subsequent data. Not only does this make for a precise type system, but also a highly generic one: both the type and the program for each instance of a family of operations can be computed from the data which codes for that instance. Recent experimental extensions to the Haskell type class mechanism give us strong tools to relativize types to other types. We may simulate some aspects of dependent typing by making counterfeit typelevel copies of data, with type constructors simulating data constructors and type classes simulating datatypes. This paper gives examples of the technique and discusses its potential. 1
Termination Checking with Types
, 1999
"... The paradigm of typebased termination is explored for functional programming with recursive data types. The article introduces , a lambdacalculus with recursion, inductive types, subtyping and bounded quanti cation. Decorated type variables representing approximations of inductive types ..."
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Cited by 36 (6 self)
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The paradigm of typebased termination is explored for functional programming with recursive data types. The article introduces , a lambdacalculus with recursion, inductive types, subtyping and bounded quanti cation. Decorated type variables representing approximations of inductive types are used to track the size of function arguments and return values. The system is shown to be type safe and strongly normalizing. The main novelty is a bidirectional type checking algorithm whose soundness is established formally.