Lightweight monadic regions

Oleg Kiselyov, Chung Chieh Shan

Research output: Chapter in Book/Report/Conference proceedingConference contribution

12 Citations (Scopus)


We present Haskell libraries that statically ensure the safe use of resources such as file handles. We statically prevent accessing an already closed handle or forgetting to close it. The libraries can be trivially extended to other resources such as database connections and graphic contexts. Because file handles and similar resources are scarce, we want to not just assure their safe use but further deallocate them soon after they are no longer needed. Relying on Fluet and Morrisett's [4] calculus of nested regions, we contribute a novel, improved, and extended implementation of the calculus in Haskell, with file handles as resources. Our library supports region polymorphism and implicit region subtyping, along with higher-order functions, mutable state, recursion, and run-time exceptions. A program may allocate arbitrarily many resources and dispose of them in any order, not necessarily LIFO. Region annotations are part of an expression's inferred type. Our new Haskell encoding of monadic regions as monad transformers needs no witness terms. It assures timely deallocation even when resources have markedly different lifetimes and the identity of the longest-living resource is determined only dynamically. For contrast, we also implement a Haskell library for manual resource management, where deallocation is explicit and safety is assured by a form of linear types. We implement the linear typing in Haskell with the help of phantom types and a parameterized monad to statically track the type-state of resources.

Original languageEnglish
Title of host publicationHaskell'08 - Proceedings of the ACM SIGPLAN 2008 Haskell Symposium
Number of pages12
Publication statusPublished - 2008
Externally publishedYes
Event1st ACM SIGPLAN Haskell Symposium, Haskell'08 - Victoria, BC, Canada
Duration: 2008 Sept 252008 Sept 25

Publication series

NameHaskell'08 - Proceedings of the ACM SIGPLAN 2008 Haskell Symposium


Other1st ACM SIGPLAN Haskell Symposium, Haskell'08
CityVictoria, BC


  • Effect systems
  • Monads
  • Parametric polymorphism
  • Regions
  • Resource management
  • Subtyping
  • Type classes
  • Type systems

ASJC Scopus subject areas

  • Computer Science Applications
  • Software
  • Electrical and Electronic Engineering


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