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Weak polymorphism can be sound

Published online by Cambridge University Press:  07 November 2008

John Greiner
Affiliation:
School of Computer Science, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, PA 15213-3891, USA
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Abstract

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The weak polymorphic type system of Standard ML of New Jersey (SML/NJ) (MacQueen, 1992) has only been presented as part of the implementation of the SML/NJ compiler, not as a formal type system. As a result, it is not well understood. And while numerous versions of the implementation have been shown unsound, the concept has not been proved sound or unsound. We present an explanation of weak polymorphism and show that a formalization of this is sound. We also relate this to the SML/NJ implementation of weak polymorphism through a series of type systems that incorporate elements of the SML/NJ type inference algorithm.

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Copyright © Cambridge University Press 1996

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