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117
Simple unificationbased type inference for GADTs
, 2006
"... Generalized algebraic data types (GADTs), sometimes known as “guarded recursive data types ” or “firstclass phantom types”, are a simple but powerful generalization of the data types of Haskell and ML. Recent works have given compelling examples of the utility of GADTs, although type inference is k ..."
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Cited by 194 (38 self)
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Generalized algebraic data types (GADTs), sometimes known as “guarded recursive data types ” or “firstclass phantom types”, are a simple but powerful generalization of the data types of Haskell and ML. Recent works have given compelling examples of the utility of GADTs, although type inference is known to be difficult. Our contribution is to show how to exploit programmersupplied type annotations to make the type inference task almost embarrassingly easy. Our main technical innovation is wobbly types, which express in a declarative way the uncertainty caused by the incremental nature of typical typeinference algorithms.
System F with type equality coercions
, 2007
"... We introduce System FC, which extends System F with support for nonsyntactic type equality. There are two main extensions: (i) explicit witnesses for type equalities, and (ii) open, nonparametric type functions, given meaning by toplevel equality axioms. Unlike System F, FC is expressive enough to ..."
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Cited by 109 (27 self)
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We introduce System FC, which extends System F with support for nonsyntactic type equality. There are two main extensions: (i) explicit witnesses for type equalities, and (ii) open, nonparametric type functions, given meaning by toplevel equality axioms. Unlike System F, FC is expressive enough to serve as a target for several different sourcelanguage features, including Haskell’s newtype, generalised algebraic data types, associated types, functional dependencies, and perhaps more besides.
Associated Types with Class
 In POPL ’05: Proceedings of the 32nd ACM SIGPLANSIGACT symposium on Principles of programming languages
, 2005
"... In this paper, we explore an extension to Haskell type classes that allows a type class declaration to define data types as well as values (or methods). Similarly, an instance declaration gives a witness for such data types, as well as a witness for each method. It turns out that this extension dire ..."
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Cited by 95 (24 self)
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In this paper, we explore an extension to Haskell type classes that allows a type class declaration to define data types as well as values (or methods). Similarly, an instance declaration gives a witness for such data types, as well as a witness for each method. It turns out that this extension directly supports the idea of a typeindexed type, and is useful in many applications, especially for selfoptimising libraries that adapt their data representations and algorithms in a typedirected manner.
Associated type synonyms
 In Proceedings of the Tenth ACM SIGPLAN International Conference on Functional Programming
, 2005
"... Haskell programmers often use a multiparameter type class in which one or more type parameters are functionally dependent on the first. Although such functional dependencies have proved quite popular in practice, they express the programmer’s intent somewhat indirectly. Developing earlier work on a ..."
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Cited by 94 (23 self)
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Haskell programmers often use a multiparameter type class in which one or more type parameters are functionally dependent on the first. Although such functional dependencies have proved quite popular in practice, they express the programmer’s intent somewhat indirectly. Developing earlier work on associated data types, we propose to add functionallydependent types as type synonyms to typeclass bodies. These associated type synonyms constitute an interesting new alternative to explicit functional dependencies.
Wobbly types: type inference for generalised algebraic data types
, 2004
"... Generalised algebraic data types (GADTs), sometimes known as “guarded recursive data types ” or “firstclass phantom types”, are a simple but powerful generalisation of the data types of Haskell and ML. Recent works have given compelling examples of the utility of GADTs, although type inference is k ..."
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Cited by 50 (2 self)
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Generalised algebraic data types (GADTs), sometimes known as “guarded recursive data types ” or “firstclass phantom types”, are a simple but powerful generalisation of the data types of Haskell and ML. Recent works have given compelling examples of the utility of GADTs, although type inference is known to be difficult. It is time to pluck the fruit. Can GADTs be added to Haskell, without losing type inference, or requiring unacceptably heavy type annotations? Can this be done without completely rewriting the alreadycomplex Haskell typeinference engine, and without complex interactions with (say) type classes? We answer these questions in the affirmative, giving a type system that explains just what type annotations are required, and a prototype implementation that implements it. Our main technical innovation is wobbly types, which express in a declarative way the uncertainty caused by the incremental nature of typical typeinference algorithms. 1
Stratified type inference for generalized algebraic data types
, 2005
"... Stratified type inference for generalized algebraic data types We offer a solution to the type inference problem for an extension of Hindley and Milner’s type system with generalized algebraic data types. Our approach is in two strata. The bottom stratum is a core language that marries type inferenc ..."
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Cited by 39 (4 self)
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Stratified type inference for generalized algebraic data types We offer a solution to the type inference problem for an extension of Hindley and Milner’s type system with generalized algebraic data types. Our approach is in two strata. The bottom stratum is a core language that marries type inference in the style of Hindley and Milner with type checking for generalized algebraic data types. This results in an extremely simple specification, where case constructs must carry an explicit type annotation and type conversions must be made explicit. The top stratum consists of (two variants of) an independent shape inference algorithm. This algorithm accepts a source term that contains some explicit type information, propagates this information in a local, predictable way, and produces a new source term that carries more explicit type information. It can be viewed as a preprocessor that helps produce some of the type annotations required by the bottom stratum. It is proven sound in the sense that it never inserts annotations that could contradict the type derivation that the programmer has in mind.
Practical RefinementType Checking
, 1997
"... Refinement types allow many more properties of programs to be expressed and statically checked than conventional type systems. We present a practical algorithm for refinementtype checking in a calculus enriched with refinementtype annotations. We prove that our basic algorithm is sound and comple ..."
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Cited by 37 (1 self)
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Refinement types allow many more properties of programs to be expressed and statically checked than conventional type systems. We present a practical algorithm for refinementtype checking in a calculus enriched with refinementtype annotations. We prove that our basic algorithm is sound and complete, and show that every term which has a refinement type can be annotated as required by our algorithm. Our positive experience with an implementation of an extension of this algorithm to the full core language of Standard ML demonstrates that refinement types can be a practical program development tool in a realistic programming language. The required refinement type definitions and annotations are not much of a burden and serve as formal, machinechecked explanations of code invariants which otherwise would remain implicit. 1 Introduction The advantages of staticallytyped programming languages are well known, and have been described many times (e.g. see [Car97]). However, conventional ty...
Concoqtion: indexed types now
 In Workshop on Partial Evaluation and SemanticsBased Program Manipulation
, 2007
"... Almost twenty years after the pioneering efforts of Cardelli, the programming languages community is vigorously pursuing ways to incorporate Fωstyle indexed types into programming languages. This paper advocates Concoqtion, a practical approach to adding such highly expressive types to fullfledged ..."
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Cited by 34 (1 self)
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Almost twenty years after the pioneering efforts of Cardelli, the programming languages community is vigorously pursuing ways to incorporate Fωstyle indexed types into programming languages. This paper advocates Concoqtion, a practical approach to adding such highly expressive types to fullfledged programming languages. The approach is applied to MetaOCaml using the Coq proof checker to conservatively extend HindleyMilner type inference. The implementation of MetaOCaml Concoqtion requires minimal modifications to the syntax, the type checker, and the compiler; and yields a language comparable in notation to the leading proposals. The resulting language provides unlimited expressiveness in the type system while maintaining decidability. Furthermore, programmers can take advantage of a wide range of libraries not only for the programming language but also for the indexed types. Programming in MetaOCaml Concoqtion is illustrated with small examples and a case study implementing a staticallytyped domainspecific language. 1.
The Gentle Art of Levitation
"... We present a closed dependent type theory whose inductive types are given not by a scheme for generative declarations, but by encoding in a universe. Each inductive datatype arises by interpreting its description—a firstclass value in a datatype of descriptions. Moreover, the latter itself has a de ..."
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Cited by 31 (8 self)
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We present a closed dependent type theory whose inductive types are given not by a scheme for generative declarations, but by encoding in a universe. Each inductive datatype arises by interpreting its description—a firstclass value in a datatype of descriptions. Moreover, the latter itself has a description. Datatypegeneric programming thus becomes ordinary programming. We show some of the resulting generic operations and deploy them in particular, useful ways on the datatype of datatype descriptions itself. Surprisingly this apparently selfsupporting setup is achievable without paradox or infinite regress. 1.
Programming with proofs and explicit contexts
 In Symposium on Principles and Practice of Declarative Programming, 2008. François Pottier and Nadji
"... This paper explores a new point in the design space of functional programming: functional programming with dependentlytyped higherorder data structures described in the logical framework LF. This allows us to program with proofs as higherorder data. We present a decidable bidirectional type syste ..."
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Cited by 30 (10 self)
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This paper explores a new point in the design space of functional programming: functional programming with dependentlytyped higherorder data structures described in the logical framework LF. This allows us to program with proofs as higherorder data. We present a decidable bidirectional type system that distinguishes between dependentlytyped data and computations. To support reasoning about open data, our foundation makes contexts explicit. This provides us with a concise characterization of open data, which is crucial to elegantly describe proofs. In addition, we present an operational semantics for this language based on higherorder pattern matching for dependently typed objects. Based on this development, we prove progress and preservation.