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A Type of Partial Recursive Functions
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A Type of Partial Recursive Functions
Ana Bove4 and Venanzio Capretta5 
| (4) |
Department of Computer Science and Engineering, Chalmers University of Technology, 412 96 Göteborg, Sweden |
| (5) |
Computer Science Institute (ICIS), Radboud University Nijmegen, |
Abstract
Our goal is to define a type of partial recursive functions in constructive type theory. In a series of previous articles,
we studied two different formulations of partial functions and general recursion. We could obtain a type only by extending
the theory with either an impredicative universe or with coinductive definitions. Here we present a new type constructor that
eludes such entities of dubious constructive credentials. We start by showing how to break down a recursive function definition
into three components: the first component generates the arguments of the recursive calls, the second evaluates them, and
the last computes the output from the results of the recursive calls. We use this dissection as the basis for the introduction
rule of the new type constructor. Every partial recursive function is associated with an inductive domain predicate; evaluation
of the function requires a proof that the input values satisfy the predicate. We give a constructive justification for the
new construct by interpreting it into the base type theory. This shows that the extended theory is consistent and constructive.
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