LISP and Symbolic Computation, 8(3)229-248
Dictionary-Free Overloading by Partial EvaluationMark P. Jones, Department of Computer Science, University of Nottingham, Nottingham NG7 2RD, UK
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Abstract: One of the most novel features in the functional
programming language Haskell is the system of type classes used to
support a combination of overloading and polymorphism. Current
implementations of type class overloading are based on the use of
dictionary values, passed as extra parameters to overloaded
functions. Unfortunately, this can have a significant effect on
run-time performance, for example, by reducing the effectiveness of
important program analyses and optimizations. This paper describes how a simple partial evaluator can be used to avoid the need for dictionary values at run-time by generating specialized versions of overloaded functions. This eliminates the run-time costs of overloading. Furthermore, and somewhat surprisingly given the presence of multiple versions of some functions, for all of the examples that we have tried so far, specialization actually leads to a reduction in the size of compiled programs. Keywords: partial evaluation, type class overloading, Haskell, specialization |
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