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Reflections on Standard ML
 FUNCTIONAL PROGRAMMING, CONCURRENCY, SIMULATION AND AUTOMATED REASONING, VOLUME 693 OF LNCS
, 1992
"... Standard ML is one of a number of new programming languages developed in the 1980s that are seen as suitable vehicles for serious systems and applications programming. It offers an excellent ratio of expressiveness to language complexity, and provides competitive efficiency. Because of its type an ..."
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Cited by 198 (4 self)
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Standard ML is one of a number of new programming languages developed in the 1980s that are seen as suitable vehicles for serious systems and applications programming. It offers an excellent ratio of expressiveness to language complexity, and provides competitive efficiency. Because of its type and module system, Standard ML manages to combine safety, security, and robustness with much of the flexibility of dynamically typed languages like Lisp. It is also has the most welldeveloped scientific foundation of any major language. Here I review the strengths and weaknesses of Standard ML and describe some of what we have learned through the design, implementation, and use of the language.
The Polymorphic Picalculus: Theory and Implementation
, 1995
"... We investigate whether the πcalculus is able to serve as a good foundation for the design and implementation of a stronglytyped concurrent programming language. The first half of the dissertation examines whether the πcalculus supports a simple type system which is flexible enough to provide a su ..."
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Cited by 95 (0 self)
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We investigate whether the πcalculus is able to serve as a good foundation for the design and implementation of a stronglytyped concurrent programming language. The first half of the dissertation examines whether the πcalculus supports a simple type system which is flexible enough to provide a suitable foundation for the type system of a concurrent programming language. The second half of the dissertation considers how to implement the πcalculus efficiently, starting with an abstract machine for πcalculus and finally presenting a compilation of πcalculus to C. We start the dissertation by presenting a simple, structural type system for πcalculus, and then, after proving the soundness of our type system, show how to infer principal types for πterms. This simple type system can be extended to include useful typetheoretic constructions such as recursive types and higherorder polymorphism. Higherorder polymorphism is important, since it gives us the ability to implement abstract datatypes in a typesafe manner, thereby providing a greater degree of modularity for πcalculus programs. The functional computational paradigm plays an important part in many programming languages. It is wellknown that the πcalculus can encode functional computation. We go further and show that the type structure of λterms is preserved by such encodings, in the sense that we can relate the type of a λterm to the type of its encoding in the πcalculus. This means that a πcalculus programming language can genuinely support typed functional programming as a special case. An efficient implementation of πcalculus is necessary if we wish to consider πcalculus as an operational foundation for concurrent programming. We first give a simple abstract machine for πcalculus and prove it correct. We then show how this abstract machine inspires a simple, but efficient, compilation of πcalculus to C (which now forms the basis of the Pict programming language implementation).
Simple Imperative Polymorphism
 LISP and Symbolic Computation
, 1995
"... . This paper describes a simple extension of the HindleyMilner polymorphic type discipline to callbyvalue languages that incorporate imperative features like references, exceptions, and continuations. This extension sacrifices the ability to type every purely functional expression that is typable ..."
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Cited by 92 (3 self)
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. This paper describes a simple extension of the HindleyMilner polymorphic type discipline to callbyvalue languages that incorporate imperative features like references, exceptions, and continuations. This extension sacrifices the ability to type every purely functional expression that is typable in the HindleyMilner system. In return, it assigns the same type to functional and imperative implementations of the same abstraction. Hence with a module system that separates specifications from implementations, imperative features can be freely used to implement polymorphic specifications. A study of a number of ML programs shows that the inability to type all HindleyMilner typable expressions seldom impacts realistic programs. Furthermore, most programs that are rendered untypable by the new system can be easily repaired. Keywords: Continuations, functional programming, polymorphism, references, state 1. Polymorphism, Imperative Features, and Modules The HindleyMilner polymorphic ty...
The Marriage of Effects and Monads
, 1998
"... this paper is to marry effects to monads, writing T for a computation that yields a value in and may have effects delimited by oe. Now we have that ( is ..."
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Cited by 92 (4 self)
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this paper is to marry effects to monads, writing T for a computation that yields a value in and may have effects delimited by oe. Now we have that ( is
A TypeTheoretic Interpretation of Standard ML
 IN PROOF, LANGUAGE AND INTERACTION: ESSAYS IN HONOUR OF ROBIN MILNER
, 2000
"... ..."
A Generalization of Exceptions and Control in MLlike Languages
 IN PROC. FPCA
, 1995
"... We add functional continuations and prompts to a language with an MLstyle type system. The operators significantly extend and simplify the control operators in SML/NJ, and can be themselves used to implement (simple) exceptions. We prove that welltyped terms never produce runtime type errors and ..."
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Cited by 61 (0 self)
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We add functional continuations and prompts to a language with an MLstyle type system. The operators significantly extend and simplify the control operators in SML/NJ, and can be themselves used to implement (simple) exceptions. We prove that welltyped terms never produce runtime type errors and give a module for implementing them in the latest version of SML/NJ.
Dynamics in ML
, 1993
"... Objects with dynamic types allow the integration of operations that essentially require runtime typechecking into staticallytyped languages. This article presents two extensions of the ML language with dynamics, based on our work on the CAML implementation of ML, and discusses their usefulness. ..."
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Cited by 56 (0 self)
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Objects with dynamic types allow the integration of operations that essentially require runtime typechecking into staticallytyped languages. This article presents two extensions of the ML language with dynamics, based on our work on the CAML implementation of ML, and discusses their usefulness. The main novelty of this work is the combination of dynamics with polymorphism.
Polymorphism and Type Inference in Database Programming
"... In order to find a static type system that adequately supports database languages, we need to express the most general type of a program that involves database operations. This can be achieved through an extension to the type system of ML that captures the polymorphic nature of field selection, toge ..."
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Cited by 38 (10 self)
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In order to find a static type system that adequately supports database languages, we need to express the most general type of a program that involves database operations. This can be achieved through an extension to the type system of ML that captures the polymorphic nature of field selection, together with a technique that generalizes relational operators to arbitrary data structures. The combination provides a statically typed language in which generalized relational databases may be cleanly represented as typed structures. As in ML types are inferred, which relieves the programmer of making the type assertions that may be required in a complex database environment. These extensions may also be used to provide static polymorphic typechecking in objectoriented languages and databases. A problem that arises with objectoriented databases is the apparent need for dynamic typechecking when dealing with queries on heterogeneous collections of objects. An extension of the type system needed for generalized relational operations can also be used for manipulating collections of dynamically typed values in a statically typed language. A prototype language based on these ideas has been implemented. While it lacks a proper treatment of persistent data, it demonstrates that a wide variety of database structures can be cleanly represented in a polymorphic programming language.
Polymorphism for Imperative Languages without Imperative Types
, 1993
"... The simple and elegant Hindley/Milner polymorphic type discipline is the basis of the type system of Standard ML, but ML's imperative features are a blight on this otherwise clean landscape. Polymorphism and imperative features cannot freely coexist without compromising type safety, hence Standard M ..."
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Cited by 29 (1 self)
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The simple and elegant Hindley/Milner polymorphic type discipline is the basis of the type system of Standard ML, but ML's imperative features are a blight on this otherwise clean landscape. Polymorphism and imperative features cannot freely coexist without compromising type safety, hence Standard ML assigns imperative types of limited polymorphism to procedures that use references, exceptions, or continuations. Several other solutions exist, but all introduce new kinds of types that complicate the type system, contaminate module signatures, and violate abstraction by revealing the pure or imperative nature of a procedure in its type. We propose a seemingly radical alternative: by restricting polymorphism to values, imperative procedures have the same types as their behaviorally equivalent functional counterparts. Although the resulting type system does not accept all expressions typable in the purely functional sublanguage, this limitation is seldom encountered in practice. The vast m...
Efficient Parallel Programming with Algorithmic Skeletons
 in Proceedings of EuroPar '96
, 1996
"... . Algorithmic skeletons are polymorphic higherorder functions representing common parallelization patterns and implemented in parallel. They can be used as the building blocks of parallel and distributed applications by integrating them into a sequential language. In this paper, we present a new ap ..."
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Cited by 23 (3 self)
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. Algorithmic skeletons are polymorphic higherorder functions representing common parallelization patterns and implemented in parallel. They can be used as the building blocks of parallel and distributed applications by integrating them into a sequential language. In this paper, we present a new approach to programming with skeletons. We integrate the skeletons into an imperative host language enhanced with higherorder functions and currying, as well as with a polymorphic type system. We thus obtain a highlevel programming language which can be implemented very efficiently. After describing a series of skeletons which work with distributed arrays, we give two examples of parallel algorithms implemented in our language, namely matrix multiplication and a statistical numerical algorithm for solving partial differential equations. Runtime measurements show that we approach the efficiency of messagepassing C up to a factor between 1 and 1.75. 1 Introduction Algorithmic skeletons repr...