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TheorySeemingly impossible programsIn case this one went under the radar, at POPL'12, Martín Escardó gave a tutorial on seemingly impossible functional programs:
A shorter version (coded in Haskell) appears in Andrej Bauer's blog. By Ohad Kammar at 20141022 09:57  Category Theory  Fun  Functional  Paradigms  Semantics  Theory  6 comments  other blogs  3304 reads
smlfamily.orgIn his blog, Bob Harper, in joint effort with Dave MacQueen and Lars Bergstrom, announces the launch of smlfamily.org:
By Ohad Kammar at 20140930 19:27  Fun  Functional  History  Implementation  Paradigms  Semantics  Theory  1 comment  other blogs  4125 reads
Inferring algebraic effectsLogical methods in computer science just published Matija Pretnar's latest take on algebraic effects and handlers:
Pretnar and Bauer's Eff has made previous appearances here on LtU. Apart from the new fangled polymorphic effect system, this paper also contains an Eff tutorial. By Ohad Kammar at 20140927 23:16  Functional  Implementation  Paradigms  Semantics  Theory  8 comments  other blogs  5971 reads
Breaking the Complexity Barrier of Pure Functional Programs with Impure Data StructuresBreaking the Complexity Barrier of Pure Functional Programs with Impure Data Structures by Pieter Wuille and Tom Schrijvers:
This paper is along the same lines a question I asked a couple of years ago. The idea here is to allow programming using immutable interfaces, and then automatically transform it into a more efficient mutable equivalent. Luca Cardelli FestschriftEarlier this week Microsoft Research Cambridge organised a Festschrift for Luca Cardelli. The preface from the book:
Hopefully the videos will be posted soon. By Ohad Kammar at 20140912 10:10  Category Theory  Lambda Calculus  Misc Books  Semantics  Theory  Type Theory  4 comments  other blogs  3724 reads
Propositions as TypesPropositions as Types, Philip Wadler. Draft, March 2014.
Philip Wadler has written a very enjoyable (Like busses: you wait two thousand years for a definition of â€œeffectively calculableâ€, and then three come along at once) paper about propositions as types that is accessible to PLTlettantes. By Manuel J. Simoni at 20140307 16:38  Fun  History  Theory  34 comments  other blogs  11726 reads
The marriage of bisimulations and Kripke logical relations
CK Hur, D Dreyer, G Neis, V Vafeiadis (POPL 2012). The marriage of bisimulations and Kripke logical relations.
There has been great progress in recent years on developing effective techniques for reasoning about program equivalence in MLlike languagesthat is, languages that combine features like higherorder functions, recursive types, abstract types, and general mutable references. Two of the most prominent types of techniques to have emerged are bisimulations and Kripke logical relations (KLRs). While both approaches are powerful, their complementary advantages have led us and other researchers to wonder whether there is an essential tradeoff between them. Furthermore, both approaches seem to suffer from fundamental limitations if one is interested in scaling them to interlanguage reasoning.I understand the paper as offering an extension to bisimulation that handles the notion of hidden transitions properly and so allows a generalisation of KLRs to any systems that can be treated using bisimulations. Applications to verified compilation are mentioned, and everything has been validated in Coq. Copatterns: the final approach to codata?Andreas Abel and Brigitte Pientka's WellFounded Recursion with Copatterns; a Unified Approach to Termination and Productivity is one of my highlights of the justfinished ICFP 2013, but it makes sense to focus on the first paper on this work, published at POPL back in January.
Codata has been often discussed here and elsewhere. See notably the discussion on Turner's Total Functional Programming (historical note: this 2004 beautification of the original 1995 paper which had much of the same ideas), and on the categorytheoryinspired Charity language. Given those precedents, it would be easy for the quick reader to "meh" on the novelty of putting "observation" first (elimination rather than introduction rules) when talking about codata; yet the above paper is the first concrete, usable presentation of an observation in a practical setting that feels right, and it solves longstanding problem that current dependentlytyped languages (Coq and Agda) have. Coinduction has an even more prominent role, due to its massive use to define program equivalence in concurrent process calculi; the relevant LtU discussion being about Davide Sangiorgi's On the origins of Bisimulation, Coinduction, and Fixed Points. The POPL'13 paper doesn't really tell us how coinduction should be seen with copatterns. It does not adress the question of termination, which is the topic of the more recent ICFP'13 paper, but I would say that the answer on that point feels less definitive. The SizeChange Termination Principle for Constructor Based LanguagesThe SizeChange Termination Principle for Constructor Based Languages, by Pierre Hyvernat:
Looks like a relatively straightforward and complete description of a termination checker based on a notion of 'sized types' limited to firstorder programs. LtU has covered this topic before, although this new paper doesn't seem to reference that particular Abel work. By naasking at 20130919 01:59  Functional  Theory  login or register to post comments  other blogs  11517 reads
Types for Flexible ObjectsTypes for Flexible Objects, by Pottayil Harisanker Menon, Zachary Palmer, Alexander Rozenshteyn, Scott Smith:
An interesting paper I stumbled across quite by accident, it purports quite an ambitious set of features: generalizing previous work on firstclass cases while supporting subtyping, mutation, and polymorphism all with full type inference, in an effort to match the flexibility of dynamically typed languages. It does so by introducing a host of new concepts that are almostbutnotquite generalizations of existing concepts, like "onions" which are kind of a typeindexed extensible record, and "scapes" which are sort of a generalization of pattern matching cases. Instead of approaching objects via a record calculus, they approach it using its dual as variant matching. Matching functions then have degenerate dependent types, which I first saw in the paper Type Inference for FirstClass Messages with MatchFunctions. Interesting aside, Scott Smith was a coauthor on this last paper too, but it isn't referenced in the "flexible objects" paper, despite the fact that "scapes" are "matchfunctions". Overall, quite a dense and ambitous paper, but the resulting TinyBang language looks very promising and quite expressive. Future work includes making the system more modular, as it currently requires whole program compilation, and adding firstclass labels, which in past work has led to interesting results as well. Most work exploiting row polymorphism is particularly interesting because it supports efficient compilation to indexpassing code for both records and variants. It's not clear if onions and scapes are also amenable to this sort of translation. Edit: a previous paper was published in 2012, A Practical, Typed Variant Object Model  Or, How to Stand On Your Head and Enjoy the View. BigBang is their language that provides syntactic sugar on top of TinyBang. Edit 2: commas fixed, thanks! By naasking at 20130904 16:57  MetaProgramming  ObjectFunctional  Theory  Type Theory  42 comments  other blogs  15206 reads

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