chrisdone

find ~/Work -name stack.yaml | xargs grep -o '^resolver: \([^#]*\)'

chrisdone

newtype Decode a =
  Decode
    { runDecode :: ByteString -> (a, ByteString)
    }
  deriving (Functor)
instance Applicative Decode where
  (<*>) = ap
  pure = return
  {-# INLINE (<*>) #-}
instance Monad Decode where

chrisdone

fix :: (a -> a) -> a
fix f = let x = f x in x

on :: (b -> b -> c) -> (a -> b) -> a -> a -> c
(.*.) `on` f = \x y -> f x .*. f y

(&) :: a -> (a -> b) -> b
x & f = f x

chrisdone

chris@precision:~/Work/chrisdone/prana$ docker run -v`pwd`:`pwd` -w`pwd` --rm ghc-compile sh -c "find /root/ghc_build -name '*.prana' -exec ls -lh {} \;"
-rw-r--r-- 1 root root 939 Jan 18 14:02 /root/ghc_build/ghc-8.0/libraries/base/base_GHC.Err.prana
-rw-r--r-- 1 root root 9.8K Jan 18 14:03 /root/ghc_build/ghc-8.0/libraries/base/base_GHC.Event.TimerManager.prana
-rw-r--r-- 1 root root 9.7K Jan 18 13:59 /root/ghc_build/ghc-8.0/libraries/base/base_Data.Bifunctor.prana
-rw-r--r-- 1 root root 9.5K Jan 18 14:00 /root/ghc_build/ghc-8.0/libraries/base/base_Data.Type.Coercion.prana
-rw-r--r-- 1 root root 9.4K Jan 18 14:05 /root/ghc_build/ghc-8.0/libraries/base/base_GHC.IO.Device.prana
-rw-r--r-- 1 root root 88 Jan 18 14:01 /root/ghc_build/ghc-8.0/libraries/base/base_Foreign.Marshal.Unsafe.prana
-rw-r--r-- 1 root root 80K Jan 18 14:07 /root/ghc_build/ghc-8.0/libraries/base/base_GHC.RTS.Flags.prana
-rw-r--r-- 1 root root 8.8K Jan 18 14:05 /root/ghc_build/ghc-8.0/libraries/base/base_GHC.IO.Buffer.prana
-rw-r--r-- 1 roo

chrisdone

Motivation

For an ADT type, such as,

data Exp = Num Int | App Char Exp
  deriving (Show)

In Haskell we have case expressions to deconstruct values, and they have exhaustiveness checking. We have

chrisdone

chrisdone

Repo                       Staleness  Issues  Stale issues  Avg. last update
commercialhaskell/hindent  89.80%     49      44            288.08 days     
commercialhaskell/intero   47.06%     17      8             71.47 days      
chrisdone/jl               83.33%     6       5             126.00 days     
fpco/odbc                  100.00%    5       5             174.40 days     
chrisdone/lucid            0.00%      5       0             2.40 days       
haskell-perf/sequences     100.00%    2       2             95.00 days      
haskell-perf/dictionaries  100.00%    1       1             158.00 days     

chrisdone

{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE PartialTypeSignatures #-}
{-# LANGUAGE ParallelListComp #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE DisambiguateRecordFields #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE OverloadedStrings #-}

chrisdone

In his talk Maybe Not, Rich Hickey explores a way of thinking about data in terms of the functions that work on them, rather than baking in any assumptions into the system directly. He's trying to take his spec system in this direction. I also have a keen interest in moving over to using records more often in typed Haskell-like languages.

An example from the slides was:

chrisdone

main = print (fib 5)

fib 0 = 0
fib 1 = 1
fib n = fib (n-1) + fib (n-2)

chrisdone

{-# LANGUAGE GADTs #-}

data Tree a where
  OneT :: Show a => a -> Tree a
  Ap   :: (Show a, Show b) => (a -> b -> c) -> Tree a -> Tree b -> Tree c

instance Show a => Show (Tree a) where
  show (OneT a) = show a
  show (Ap _ x y) = "" ++ show x ++ "," ++ show y ++ ""