HERMIT plugin for optimizing Scrap-Your-Boilerplate traversals.
A HERMIT plugin for GHC which optimizes SYB generic traversals to achieve equivalent performance to hand-written traversals.
Details can be found in the paper: http://michaeldadams.org/papers/syb-opt/
Note: This compiler plugin requires GHC 7.8 (or HEAD) and specially compiled copies of base, ghc-prim, and syb. Up-to-date instructions can be found at: https://github.com/ku-fpg/hermit/wiki/GHC-HEAD. We are working to lift these requirements.
As an example, we apply the optimization to Foo.hs, which contains the following code:
module Main where
import Data.Generics
import HERMIT.Optimization.SYB.Prelude
main :: IO ()
main = print (mapInt (+1) [1..10])
mapInt :: (Int -> Int) -> [Int] -> [Int]
mapInt f = everywhere (mkT f)
Note that importing HERMIT.Optimization.SYB.Prelude is required in any module targeted for optimization.
To compile Foo.hs with the optimization:
$ hermit Foo.hs -opt=HERMIT.Optimization.SYB +Main mapInt
This invokes GHC with a specific set of flags. These flags may be used instead of the hermit program itself, or placed in a cabal file.
The first argument to HERMIT is the target file. Next is the -opt flag, which specifies the plugin name. Then follows one or more target module names, each beginning with a plus sign. After each target module is a list of targeted functions. The distinguished interactive target will run the optimization on any other targets and then enter the HERMIT interactive shell. The distinguished 'interactive-only' target will open the HERMIT shell before optimization. HERMIT commands specific to this optimization are available for interactive use.