#10958: "Annotating pure code for parallelism" docs based on old par/pseq primitives -------------------------------------+------------------------------------- Reporter: robstewartuk | Owner: Type: bug | Status: new Priority: lowest | Milestone: Component: Documentation | Version: 7.10.2 Keywords: parallelim | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The example code in GHC 7.10.2 docs "7.28. Concurrent and Parallel Haskell", then in "7.15.4. Annotating pure code for parallelism" the recommendation is to use `par` and `pseq`. These primitives pre-dates the strategy combinators `rpar` and `rseq`. The example given is: {{{#!hs import Control.Parallel nfib :: Int -> Int nfib n | n <= 1 = 1 | otherwise = par n1 (seq n2 (n1 + n2 + 1)) where n1 = nfib (n-1) n2 = nfib (n-2) }}} The paper "Seq no more: Better Strategies for Parallel Haskell" ([http://www.macs.hw.ac.uk/~hwloidl/publications/strategies10.pdf]) advocates `Eval` as an "evaluation order" monad, as preferable (versus `par` and `seq`) for loose control of evaluation order of parallelism. Moreover, Simon Marlow's "Parallel and Concurrent Programming in Haskell" doesn't mention the `par` and `seq` primitives at all. Should the GHC docs for "Concurrent and Parallel Haskell" encourage the use Eval combinators, either in addition to or instead of the `par` and `seq` primitives? I'd be happy to contribute an update to the docs if people agree to a shift in emphasis towards the Eval monad in the docs. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10958 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler