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Summary: An Indexed Model of Impredicative Polymorphism and Mutable References
Amal Ahmed Andrew W. Appel Roberto Virga
Princeton University
{amal,appel,rvirga}@cs.princeton.edu
Abstract
We present a semantic model of the polymorphic lambda
calculus augmented with a higher-order store, allowing the
storage of values of any type, including impredicative quan-
tified types, mutable references, recursive types, and func-
tions. Our model provides the first denotational semantics
for a type system with updatable references to values of im-
predicative quantified types. The central idea behind our
semantics is that instead of tracking the exact type of a mu-
table reference in a possible world our model keeps track
of the approximate type. While high-level languages like
ML and Java do not themselves support storage of impred-
icative existential packages in mutable cells, this feature is
essential when representing ML function closures, that is, in
a target language for typed closure conversion of ML pro-
grams.
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