steshaw

#!/bin/bash

set -eu

source <(HALCYON_NO_SELF_UPDATE=1 /app/halcyon/halcyon paths)
HALCYON_NO_SELF_UPDATE=1 /app/halcyon/halcyon install \
    --ghc-version=7.10.1 \
    --app-no-strip

steshaw

$ cabal2nix --shell . >shell.nix
$ nix-shell -I ~ --command 'cabal configure'
these derivations will be built:
  /nix/store/rbij827rx40bgs6122b2n929b79z0rgy-ghc-7.10.1.drv
building path(s) ‘/nix/store/957j0j7a51xzi3bbl8ym11ha7gkg5jz8-ghc-7.10.1’
created 481 symlinks in user environment
There are problems in package conduit-extra-1.1.7.3:
  dependency "attoparsec-0.12.1.6-2dceb091855fa2d2aff2ca4101afc493" doesn't exist
  dependency "text-1.2.0.4-98506efb1b9ada233bb5c2b2db516d91" doesn't exist
There are problems in package hakyll-4.6.8.1:

steshaw

function work(workQ) {
  task, workQ_ ← pop(workQ)
  do(task)
  work(workQ_)
}
work(workQ)

steshaw

#!/usr/bin/env zsh

set -eu

unset FOO

if [[ ${FOO:-} == 'hi' ]]; then
  echo "It is 'hi'"
fi
if [[ ${FOO:-} == '' ]]; then

steshaw

perspectives on streams performance

In order to get the full benefit from JDK 8 streams we will need to make them optimize fully. Here are a few thoughts about that.

I think of streams as a more concise and orderly replacement of classic "for" loops. Every stream can be rewritten as one or more for-loops, at the cost of verbosity and commitment to hard-coding optimizations (like FJ).

A classic "for" loop is a external iterator notation: The iteration machinery is outside of (lexically around) the data structure access. This notation is at least as old as Fortran. Streams are an internal iteration notation: The iteration machinery (crucially, the looping part of the algorithm) is inside the data structure, and only the loop body appears in the user code (as a lambda). This notation is also old, found in Lisp and Smalltalk.

External iterators are easier to optimize, because their crucial iteration logic is always

steshaw

class Hash
  def safe_invert
    lazy
      .map {|a, b| [b, a]}
      .group_by {|a| a[0]}
      .map {|a, b| [a, b.collect {|c| c[1]}]}
      .to_h
  end
end

steshaw

#!/usr/bin/env runhaskell

import Data.List (stripPrefix, intercalate)

main = do
  contents <- getContents 
  mapM_ munge $ lines contents

munge :: String -> IO ()
munge url = case stripPrefix "https://steshaw.wordpress.com" url of

steshaw

#!/usr/bin/env runhaskell-sandbox parsec

import Data.List (stripPrefix, intercalate)
import Text.Parsec
import Text.Parsec.Char
import Debug.Trace

main = do
  contents <- getContents
  let ls = lines contents

steshaw

import System.Environment (getArgs)
import Control.Monad (forM_)
import Text.ParserCombinators.Parsec (spaces, char, chainl1, runParser)
import Text.ParserCombinators.Parsec.Number (int)

infixOp = do
  spaces
  char '+'
  spaces
  return (+)

steshaw

Prelude> putStrLn "\x03bb\x03a0"
λΠ