hmaurer

require 'tire'
require 'nobrainer'

NoBrainer.connect 'rethinkdb://server/company'

class Employee
  include NoBrainer::Document

  field :name
  field :title

hmaurer

This is my recommended path for learning Haskell.

Something to keep in mind: don't sweat the stuff you don't understand immediately. Just keep moving.

Primary course

Installing Haskell

Ubuntu PPA

hmaurer

module Printf

%default total

data Format = FInt Format -- %d
            | FString Format -- %s
            | FOther Char Format -- [a-zA-Z0-9]
            | FEnd --

format : List Char -> Format

hmaurer

suc (a + suc b)   == suc (b + suc a)
        ^
        |
        |
suc (suc (a + b)) == suc (b + suc a)
                             ^
                             |
                             |
suc (suc (a + b)) == suc (suc (b + a))
                   ^

hmaurer

... = begin
        suc (a + suc b)
      ==< cong suc (lemma2 a b) >
        suc (suc (a + b))
      ==< cong (suc.suc) (comm a b) >
        suc (suc (b + a))
      ==< cong suc (sym (lemma2 b a)) >
        suc (b + suc a)
      []

hmaurer

Useful Scalac Flags

So, there have been some discussions and angry tweets recently about irritating Scala "features" (like value discarding and auto-tupling) that can actually be turned off by selecting the right compiler flag in conjunction with -Xfatal-warnings. I highly recommend a set of options something like those below.

scalacOptions ++= Seq(
  "-deprecation",           
  "-encoding", "UTF-8",       // yes, this is 2 args
  "-feature",                
 "-language:existentials",

hmaurer

apply :: (t -> a) -> (t -> b) -> (a, b)
apply f g x = (f x, g x)

hmaurer

sumUpTo :: Int -> [(Int, Int)]
sumUpTo n = map (\x -> (x, n - x)) [0..n]

mult xs ys = do
	cs <- map sumUpTo [0..maxCoef]
	return (sum $ map g $ filter f cs)
	where
		maxCoef = length xs + length ys - 2
		f (x, y) = x < length xs && y < length ys
		g (x, y) = (xs !! x) * (ys !! y)

hmaurer

// This is the structure of the binary nbt file
TAG_Compound('Level') {
	TAG_Compound('nested compound test') {
		TAG_Compound('egg') {
			TAG_String('name'): 'Eggbert'
			TAG_Float('value'): 0.5
		}
		TAG_Compound('ham') {
			TAG_String('name'): 'Hampus'
			TAG_Float('value'): 0.75

hmaurer

// Index of maximum: j
int j = 0;
for (int i = 1; i < array.length; i++) {
  if (array[i] > array[j]) j = i;
}