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Monadic Regions

This paper explores the integration of monadic structures with region-based memory management to enhance the management of object lifetimes in pure programming languages. By introducing a monadic sub-language, we bridge the two lines of research: region algebras and monadic effects. We present the design of a region monad, RGN, and demonstrate how it encapsulates region computations and memory allocation through efficient type constructs. Our work lays the foundation for sophisticated type-preserving translations and the encapsulation of imperative features within pure languages.

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Monadic Regions

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  1. Monadic Regions Matthew Fluet Cornell University

  2. Introduction • Draw together two lines of research • Region-based memory management • Regions delimit lifetimes of objects • new .e • Monadic encapsulation of effects • Embed imperative features in pure languages • runST :: .(s. ST s )  

  3. Introduction • Encode Tofte-Talpin region calculus in System F with monadic sub-language • Features • runST serves as inspiration • runRGN – encapsulate region computation • newRGN – encapsulate a single region • Sufficient polymorphism to encode region polymorphism

  4. FRGN = System F + RGN monad • System F • Monadic (sub)-language • Monadic types and operations • RGN r – monadic region computations • RGNVar r – region allocated values • RGNHandle r – region handles

  5. FRGN = System F + RGN monad • Create and read region allocated values allocRGNVar :: ,r.   RGNHandle r  RGN r (RGNVar r ) readRGNVar :: ,r. RGNVar r   RGN r 

  6. FRGN = System F + RGN monad • Encapsulate and run a monadic computation runRGN :: .(r. RGNHandle r  RGN r )  

  7. FRGN = System F + RGN monad • Encapsulate a region newRGN :: ,r.(s. RGNHandle s  RGN s )  RGN r 

  8. FRGN = System F + RGN monad • Encapsulate a region newRGN :: ,r.(s. r  s  RGNHandle s  RGN s )  RGN r α  ≡ ,r,s. RGN r   RGN s 

  9. Single Effect Calculus • LIFO stack of regions imposes a partial order on live (allocated) regions • Regions lower on the stack outlive regions higher on the stack • A single region can serve as a witness for a set of effects • Region appears as a single effect in place of the set

  10. Translation • Type-preserving translation from Single Effect Calculus to FRGN new .e newRGN (.w.h. e)

  11. Conclusion • Monadic encoding of effects applicable to region calculi • Trivial (syntactic) equality on types • Encapsulation within monad

  12. FRGN = System F + RGN monad • Monadic unit and bind returnRGN :: ,r.   RGN r  thenRGN :: ,,r. RGN r  ( RGN r )  RGN r 

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