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The following shows that the latest nixos-unstable channel has all the transitive dependencies for haskellPackages.lens available for fetching from the binary cache:

$ nix-env -f https://releases.nixos.org/nixos/unstable/nixos-18.09pre149415.8395f9aa85e/nixexprs.tar.xz \
  -iA haskellPackages.lens --dry-run
(dry run; not doing anything)
installing 'lens-4.16.1'
these paths will be fetched (136.28 MiB download, 1899.17 MiB unpacked):

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NixOS Installer Ideas

Background

I recently installed NixOS from scratch on a new device and since I haven’t needed to do this in 1.5 years I forgot the sequence needed and made a whole bunch of mistakes.

It would be nice to be able to improve the experience and guide the user. On the other end of the installer UX are assisted installers which often use insecure defaults (e.g. for partitioning, or default passwds, etc).

nixos-help is potentially a valuable tool here but the documentation could use some attention in terms of organization, flow, and ensuring the documentation is updated to the current release of NixOS it is shipped with.

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{ stdenv, fetchurl, gtk2, xorg, patchelf, unzip, makeWrapper, jre }:
let version = "1.5.6"; in
stdenv.mkDerivation rec {
  inherit version;
  name = "TLAToolBox-${version}";

  src = fetchurl {
    url = "https://tla.msr-inria.inria.fr/tlatoolbox/products/TLAToolbox-${version}-linux.gtk.x86_64.zip";
    sha256 = "1b5sf4d7sv0x1hg4f1if3q7wzsi09dr8fv71qfagj8m25zrh3lvj";
  };

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# Put in your ~/.ssh/config

### Problem
#
# You are on a public WiFi network that blocks SSH ports but you don't want to switch 
# to pushing your Github changes to GH remotes via HTTPS nor do you want to change the
# remote hostname in all your repos.

Host github.com
  Hostname ssh.github.com

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{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE RankNTypes        #-}
module FooBarBaz.Main
  ( compose3a
  , compose3b
  , compose3c
  , main
  ) where

{-

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#!/usr/bin/env bash

function usage() {
  >&2 echo "Usage: $0 SOURCE_URL PROXY_URL"
}

function main() {
  local -r source_url="${1}"
  local -r proxy_url="${2}"
  curl \

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node_modules

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/*
  SP: currying this gives the type: (T => T) => T => T
  That looks an awful lot like Haskell's application ($) operator. :)
  There is a higher order abstraction here, sniff it out.
*/
type ChurchNumeral[T] = (T => T, T) => T

def cn0[T](f:T=>T, x:T):T = x
def cn1[T](f:T=>T, x:T):T = f(x)
def cn2[T](f:T=>T, x:T):T = f(f(x))

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$ ruby bench/lazy.rb
                                                                                                           user     system      total        real
using Range#lazy                                                                                       0.330000   0.000000   0.330000 (  0.330689)
using Enumerator#yield                                                                                 0.170000   0.000000   0.170000 (  0.177117)
using Fiber#yield                                                                                      0.340000   0.120000   0.460000 (  0.458015)

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-- module of natural number properties ... and stuff
module Naturally where

import Prelude hiding (even, odd)

-- recursive data structure
data Nat = Zero     -- base case is "zero" 
         | Succ Nat -- successor of another Nat is the "recursive" case data constructor
         deriving (Eq)