The recursive record semantics of objects revisited

Abstract

In a call-by-value language, representing objects as recursive records requires using an unsafe fixpoint. We design, for a core language including extensible records, a type system which rules out unsafe recursion and still supports the construction of a principal type for each typable term. We illustrate the expressive power of this language with respect to object-oriented programming by introducing a sub-language for “mixin-based” programming.

Compilation of extended recursion in call-by-value functional languages

“…We say that the right-hand side strongly depends on f . Several techniques to check this condition have been proposed [3,14,12,8].…”

Mixin Modules and Computational Effects

“…More recently, [HL02] has considered a CMS-like calculus, called CMS v , with a refined type system in order to avoid bad recursion in a call-by-value setting. A separate compilation schema for CMS v has been also investigated by means of a translation down to a call-by-value λ-calculus λ B extended with a non-standard let rec construct, inspired by the calculus defined in [Bou02]. Like CMS do , both λ B and the calculus of Boudol serve as semantic basis for programming languages supporting mixins and introduce non-standard constructs for recursion which can produce terms having an undefined semantics.…”

“…Like CMS do , both λ B and the calculus of Boudol serve as semantic basis for programming languages supporting mixins and introduce non-standard constructs for recursion which can produce terms having an undefined semantics. However, λ B does not have imperative features, whereas the calculus in [Bou02] does not allow recursion in the presence of side-effects. For instance, in CMS do the term mdo (x ⇐ new(x); ret(x)) has a well-defined semantics, whereas the corresponding translated term let rec x = ref x in x in Boudol's calculus is not well-typed; indeed, the evaluation of this term gets stuck.…”

“…On the other hand, the more refined type systems adopted in [HL02,Bou02] are able to statically detect all bad recursive declarations. As already mentioned, the definition of the mdo construct in CMS do is inspired by the work on the semantics of recursive monadic bindings in Haskell [EL00,ELM01,ELM02,EL02].…”

“…Since the emphasis of the paper is on the operational aspects, we adopt a simple type system like that for Haskell, that does not detect dynamic errors related to bad recursive declarations; for instance, doall([; x ⇐ set(y, 1), y ⇐ new(0)]) is a well-typed term which evaluates into a dynamic error. However, more refined type systems based on dependencies analysis [Bou02,HL02] could be considered for CMS do in order to avoid this kind of dynamic errors. The rest of the paper is organized as follows.…”