ndmitchell

I suspect the below isn't a good idea, because the remember needs repeating lots of times for every user of a rule. The new design seems to eliminate these issues more cleanly, but it's an interesting point in the design space.

Rethinking Rules

The current Rule typeclass has a number of issues. It's a bit complex to use, it often results in more dependencies than you were hoping, it's hard to control. People often end up defining oracles instead or rules but then you don't get options for other things. This document attempts to rethink that.

Concept

Shake runs rules that produce values. These rules track the current state of the system (other rules) and external values (files on disk). Currently the value produced by a rule is tracked automatically. This is often awkward. Imagine we want:

ndmitchell

Each key gets intern'd into an Id


Key :-> Id

Id :-> Status

ndmitchell

{-# LANGUAGE Rank2Types #-}

import qualified Core.IO as F
import qualified Core.String as F
import qualified Core.Array as F
import qualified Core.VFS as F
import qualified Data.ByteString.Lazy as LBS
import qualified Data.ByteString as BS
import Codec.Compression.GZip as GZip
import Codec.Archive.Tar as Tar

ndmitchell

	Tue Jan 24 08:33 2017 Time and Allocation Profiling Report  (Final)

	   hlint +RTS -p -RTS src

	total time  =        2.27 secs   (2274 ticks @ 1000 us, 1 processor)
	total alloc = 42,443,280,112 bytes  (excludes profiling overheads)

COST CENTRE   MODULE                                %time %alloc

uniplateData  Data.Generics.Uniplate.Internal.Data   41.4   68.1

ndmitchell

Haskell can be written using nothing more than a text editor, and most popular editors include Haskell syntax highlighting out of the box. In addition, some editors can be enhanced to provide IDE-like features, using the tools listed below.

Intero (Emacs enhancement)

• Provides instant error feedback, completions, go to definition, applying suggestions, type of expression.
• Works with GHC 7.8 onwards, benefits from Stack.

ndmitchell

{-# OPTIONS_GHC -O2 #-}
import Control.Monad
import Control.Exception
import System.Time.Extra

import Criterion.Main

type DList a = [a] -> [a]

dTo f = f []

ndmitchell

	Thu Jun 01 08:33 2017 Time and Allocation Profiling Report  (Final)

	   hlint +RTS -P -RTS src

	total time  =        1.24 secs   (1242 ticks @ 1000 us, 1 processor)
	total alloc = 2,511,288,344 bytes  (excludes profiling overheads)

COST CENTRE                   MODULE                                %time %alloc  ticks     bytes

unifyExp                      Hint.Match                             23.0    2.0    286  49844616

ndmitchell

 TOT   INH   IND
51.0  47.4     -  Hint.Match readMatch (53)
12.0  12.0     -  Data.Generics.Uniplate.Internal.Data readCacheFollower (3)
10.3  10.2    .6  Language.Haskell.Exts parseFileContentsWithComments (53)
 8.7   7.5   7.5  Data.Generics.Uniplate.Internal.Data uniplateData (1377837)
99.9   5.2     -  MAIN MAIN (0)
 2.9   2.8   2.0  Data.Generics.Uniplate.Internal.Data descendBiData (109203)
 2.4   2.4     -  HSE.All runCpp (53)
 2.3   2.3   2.3  Data.Generics.Uniplate.Internal.Data typeKey (2721430)
 1.9   1.5   1.5  Data.Generics.Uniplate.Internal.Data fromOracle (1031785)

ndmitchell

import System.Environment
import System.Directory.Extra
import Control.Exception.Extra
import System.FilePath
import Control.Monad
import System.IO.Extra
import Data.List.Extra

main = do
    [dir,out] <- getArgs

ndmitchell

This is intended as a reply to https://ro-che.info/articles/2017-06-12-friendly-contributing-policies, but I don't really want it to be a blog post (it's not the right level for my blog), and that blog doesn't have comments, and I don't want to mis-express myself in 120 characters or whatever. So here goes a gist :)

Firstly, as to the talk, the context was read around the project, and figure out if it will suit you. I am deliberately quoting haskell-src-exts out of context, and deliberately not saying where either quote came from. I appreciate the full policy is much more welcoming than that one snippet would imply.

However, when I wanted to find an unfriendly contributing policy, I immediately thought of haskell-src-exts. I do genuinely find the document, as a whole, quite unwelcoming. I appreciate that languages sound different to native speakers, and it didn't stop me contributing, but it did give me pause. Whether a document is friendly or not is a feeling, and so by explaining why I have that feeling