FuSe is a lightweight OCaml module that implements the session-based communication primitives in and enables session type checking and inference. It works with any out-of-the-box installation of OCaml and supports the following features:
For questions, suggestions and bug reports please contact Luca Padovani.
You need OCaml to compile FuSe.
Compile the library and the examples:
Test an example:
Test session type inference:
cd examples make Tmath.st
Users may refer to the API documentation extracted with
ocamldoc and to the tutorial.
The principles and internals of FuSe are described in .
Below is an almost verbatim transcription in OCaml+FuSe of the bookshop example found in .
module Session = Session.Bare let rec shopLoop s order = match Session.branch s with | `Add s -> let book, s = Session.receive s in shopLoop s (book :: order) | `CheckOut s -> let card, s = Session.receive s in let address, s = Session.receive s in Session.close s let shop shopAccess = shopLoop (Service.accept shopAccess)  let isChildrensBook book = true let voucher card address c book = let c = if isChildrensBook book then let c = Session.select (fun x -> `Add x) c in Session.send book c else c in let c = Session.select (fun x -> `CheckOut x) c in let c = Session.send card c in let c = Session.send address c in Session.close c; book let mother card address shopAccess sonAccess book = let c = Service.request shopAccess in let c = Session.select (fun x -> `Add x) c in let c = Session.send book c in let s = Service.request sonAccess in let s = Session.send (voucher card address c) s in let sonBook, s = Session.receive s in Session.close s let son sonAccess book = let s = Service.accept sonAccess in let f, s = Session.receive s in let s = Session.send (f book) s in Session.close s let _ = let mCard = "0123 4567 7654 3210" in let mAddress = "17 session type rd" in let mBook = "Life of Ada Lovelace" in let sBook = "Types and programming languages" in let shopAccess = Service.create () in let sonAccess = Service.create () in let _ = Thread.create shop shopAccess in let _ = Thread.create (son sonAccess) sBook in mother mCard mAddress shopAccess sonAccess mBook
Here are the (session) types inferred by OCaml, pretty printed in a
more readable form by the
rosetta utility that accompanies the
library (the tutorial gives the correspondence between
OCaml types and this notation). Note the amount of parametric
polymorphism compared to the typing of the example as given in
val shopLoop : rec X.&[ Add: ?α.X | CheckOut: ?β.?γ ] → α list → unit val shop : rec X.&[ Add: ?α.X | CheckOut: ?β.?γ ] Service.t → unit val isChildrensBook : α → bool val voucher : α → β → rec X.⊕[ Add: !γ.X | CheckOut: !α.!β ] → γ → γ val mother : α → β → &[ Add: ?γ.rec X.&[ Add: ?δ.X | CheckOut: ?α.?β ] ] Service.t → ?(δ → δ).!ε Service.t → γ → unit val son : ?(α → β).!β Service.t → α → unit
Simon J. Gay, Vasco T. Vasconcelos, Linear type theory for asynchronous session types, Journal of Functional Programming, 2010.
Peter Thiemann and Vasco T. Vasconcelos: Context-Free Session Types, Proceedings of ICFP’16, 2016.
Luca Padovani: Context-Free Session Type Inference, Proceedings of ESOP’17, 2017.
Simon J. Gay and Malcolm Hole: Subtyping for session types in the pi calculus, Acta Informatica, 2005.
Luca Padovani: A Simple Library Implementation of Binary Sessions, Journal of Functional Programming, 2017.