The semantics of the untyped (call-by-name) lambda-calculus is a well developed field built around the concept of solvable terms, which are elegantly characterized in many different ways. In particular, unsolvable terms provide a consistent notion of meaningless term. The semantics of the untyped call-by-value lambda-calculus (CbV) is instead still in its infancy, because of some inherent difficulties but also because CbV solvable terms are less studied and understood than in call-by-name. On the one hand, we show that a carefully crafted presentation of CbV allows us to recover many of the properties that solvability has in call-by-name, in particular qualitative and quantitative characterizations via multi types. On the other hand, we stress that, in CbV, solvability plays a different role: identifying unsolvable terms as meaningless induces an inconsistent theory.

@article{paperbot1501,
  title = {The theory of call-by-value solvability},
  author = {Beniamino Accattoli and Giulio Guerrieri},
  journal = {Proceedings of the ACM on Programming Languages},
  volume = {6},
  number = {ICFP},
  year = {2022},
  doi = {10.1145/3547652}
}