Conference paper Open Access

Implementing Baker's SUBTYPEP decision procedure

Valais Léo; Newton Jim; Verna Didier

We present here our partial implementation of Baker’s decision
procedure for subtypep . In his article “A Decision Procedure for
Common Lisp’s SUBTYPEP Predicate”, he claims to provide imple-
mentation guidelines to obtain a subtypep more accurate and as
efficient as the average implementation. However, he did not pro-
vide any serious implementation and his description is sometimes
obscure. In this paper we present our implementation of part of his
procedure, only supporting primitive types, Clos classes, member ,
range and logical type specifiers. We explain in our words our un-
derstanding of his procedure, with much more detail and examples
than in Baker’s article. We therefore clarify many parts of his de-
scription and fill in some of its gaps or omissions. We also argue in
favor and against some of his choices and present our alternative
solutions. We further provide some proofs that might be missing
in his article and some early efficiency results. We have not re-
leased any code yet but we plan to open source it as soon as it is

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