What I learned from Seven Languages in Seven Weeks (IPRUG)
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This document discusses seven programming languages that the author learned over seven weeks: Ruby, Io, Prolog, Scala, Erlang, Clojure, and Haskell. For each language, it provides a brief description and comparison of the language's features, strengths, and weaknesses. It discusses concepts like variables, functions, objects, concurrency, and more for each programming paradigm. The document aims to compare and contrast the languages at a high level based on the author's experiences learning them.
![Tuples
?- (X, Y, Z) = (1, 2, "foo").
X = 1,
Y = 2,
Z = [102, 111, 111].
?- (X, _, Z) = (1, 2, "foo").
X = 1,
Z = [102, 111, 111].](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-31-320.jpg)
![Calculation with lists
sum(0, []).
sum(Total, [Head|Tail]) :-
sum(Sum, Tail),
Total is Head + Sum.
?- sum(What, [1, 2, 3]).
What = 6.](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-32-320.jpg)
![Solving (4×4) sudoku
?- sudoku([_, _, 2, 3,
_, _, _, _,
_, _, _, _,
3, 4, _, _],
Solution).
Solution = [4,1,2,3,2,3,4,1,1,2,3,4,3,4,1,2].](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-33-320.jpg)
![Solving (4×4) sudoku
valid([]).
valid([Head|Tail]) :-
all_different(Head),
valid(Tail).
sudoku(Puzzle, Solution) :-
Solution = Puzzle,
Puzzle = [S11, S12, S13, S14,
S21, S22, S23, S24,
S31, S32, S33, S34,
S41, S42, S43, S44],
Solution ins 1..4,
Row1 = [S11, S12, S13, S14], Row2 = [S21, S22, S23, S24],
Row3 = [S31, S32, S33, S34], Row4 = [S41, S42, S43, S44],
Col1 = [S11, S21, S31, S41], Col2 = [S12, S22, S32, S42],
Col3 = [S13, S23, S33, S43], Col4 = [S14, S24, S34, S44],
Square1 = [S11, S12, S21, S22], Square2 = [S13, S14, S23, S24],
Square3 = [S31, S32, S41, S42], Square4 = [S33, S34, S43, S44],
valid([Row1, Row2, Row3, Row4,
Col1, Col2, Col3, Col4,
Square1, Square2, Square3, Square4]).](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-34-320.jpg)
![Lists, sets & maps
scala> val list = List("one", "two", 3)
list: List[Any] = List(one, two, 3)
scala> list(1)
res0: Any = two
scala> Set(1, 2, 3) ++ Set(2, 3, 4)
res1: scala.collection.immutable.Set[Int] = Set(1, 2, 3, 4)
scala> val map = Map(1 -> "One", 2 -> "Two")
map: scala.collection.immutable.Map[Int,java.lang.String] =
Map(1 -> One, 2 -> Two)
scala> map(1)
res2: java.lang.String = One](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-45-320.jpg)
![Heads and tails
scala> val list = List("one", "two", "three")
list: List[java.lang.String] = List(one, two, three)
scala> list.head
res0: java.lang.String = one
scala> list.tail
res1: List[java.lang.String] = List(two, three)
scala> list.init
res2: List[java.lang.String] = List(one, two)
scala> list.last
res3: java.lang.String = three](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-46-320.jpg)
![List processing
scala> val jedi = List("Yoda", "Obiwan", "Luke")
jedi: List[java.lang.String] = List(Yoda, Obiwan, Luke)
scala> jedi.filter(name => name.size < 5)
res0: List[java.lang.String] = List(Yoda, Luke)
scala> jedi.map(name => name.size)
res1: List[Int] = List(4, 6, 4)
scala> val numbers = List(1, 2, 3)
numbers: List[Int] = List(1, 2, 3)
scala> numbers.foldLeft(0)((a, n) => a + n)
res2: Int = 6](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-47-320.jpg)
![The usual types (mostly)
1> 2 + 2.
4
2> "Hello".
"Hello"
3> atom.
atom
4> {foo, 123, "bar"}.
{foo,123,"bar"}
5> [1, "one", two].
[1,"one", two]
6> [87, 84, 70, 63].
"WTF?"](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-56-320.jpg)
![Pattern matching
1> Pet = {{name, "Zorro"}, {type, "Cat"}}.
{{name,"Zorro"},{type,"Cat"}}
2> {{name, Name}, {type, Type}} = Pet.
{{name,"Zorro"},{type,"Cat"}}
3> Name.
"Zorro"
4> Type.
"Cat"
5> [Head|Tail] = [foo, bar, baz].
[foo,bar,baz]
6> {Head, Tail}.
{foo,[bar,baz]}](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-58-320.jpg)
![Bit matching
1> [A, B, C, D] = [1, 0, 50, 200].
[1,0,50,200]
2> Packed = <<A:1, B:1, C:6, D:8>>.
<<"²È">>
3> <<P:1, Q:1, R:6, S:8>> = Packed.
<<"²È">>
4> {P, Q, R, S}.
{1,0,50,200}](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-59-320.jpg)
![Basic functions
-module(demo).
-export([echo/1]).
echo(Anything) -> Anything.
1> c(demo).
{ok,demo}
5> demo:echo("Hello").
"Hello"
6> demo:echo(42).
42](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-60-320.jpg)
![Patterns in functions
-module(fact).
-export([fact/1]).
fact(0) -> 1;
fact(N) -> N * fact(N-1).
1> c(fact).
{ok,fact}
3> fact:fact(6).
720
4> fact:fact("foo").
** exception error: bad argument in an arithmetic
expression
in function fact:fact/1 (fact.erl, line 5)
6> fact:fact(10000).](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-61-320.jpg)
![Control structures
1> List = [1, 2, 3].
[1,2,3]
2> case List of
2> [] -> none;
2> [_|[]] -> one;
2> _ -> some
2> end.
some
3> A = 42.
42
4> if
4> A < 10 -> small;
4> A < 100 -> big;
4> true -> massive
4> end.
big](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-65-320.jpg)
![Higher order functions
1> Double = fun(X) -> X * 2 end.
#Fun<erl_eval.6.111823515>
2> Double(2).
4
3> List = [1, 2, 3].
[1,2,3]
4> lists:map(Double, List).
[2,4,6]
5> lists:map(fun(X) -> X + 1 end, List).
[2,3,4]
6> lists:foldl(fun(X, Sum) -> X + Sum end, 0, List).
6](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-66-320.jpg)
![Building lists
-module(double).
-export([double_all/1]).
double_all([]) -> [];
double_all([H|T]) -> [H * 2|double_all(T)].
1> c(double).
{ok,double}
2> double:double_all([1, 2, 3, 4]).
[2,4,6,8]](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-67-320.jpg)
![List comprehensions
1> Numbers = [1, 2, 3, 4].
[1,2,3,4]
2> Double = fun(X) -> X * 2 end.
#Fun<erl_eval.6.111823515>
3> lists:map(Double, Numbers).
[2,4,6,8]
4> [Double(X) || X <- Numbers].
[2,4,6,8]
5> [X || X <- Numbers, X > 1, X < 4].
[2,3]
6> Basket = [{pencil, 4, 0.25}, {pen, 1, 1.20}, {paper, 2, 1.00}].
[{pencil,4,0.25},{pen,1,1.2},{paper,2,1.0}]
7> Totals = [{Item, Qty * Price} || {Item, Qty, Price} <- Basket].
[{pencil,1.0},{pen,1.2},{paper,2.0}]](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-68-320.jpg)
![Message loops
-module(doubler).
-export([loop/0]).
loop() ->
receive
N ->
io:format("~b~n", [N * 2]),
loop()
end.
18> Doubler = spawn(fun doubler:loop/0).
<0.87.0>
19> Doubler ! 2.
4
2](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-70-320.jpg)
![Synchronous messages
-module(doubler).
-export([loop/0, double/2]).
loop() ->
receive
{Pid, N} ->
Pid ! (N * 2),
loop()
end.
double(To, N) ->
To ! {self(), N},
receive
Result -> Result
end.
27> Doubler = spawn(fun doubler:loop/0).
<0.118.0>
28> doubler:double(Doubler, 3).
6](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-71-320.jpg)
![Monitor and restart
-module(monitor).
-export([loop/0, start/0]).
loop() ->
process_flag(trap_exit, true),
receive
new ->
register(doubler, spawn_link(fun doubler:loop/0)),
loop();
{'EXIT', From, Reason} ->
io:format("~p exited: ~p.", [From, Reason]),
monitor ! new,
loop()
end.
start() ->
register(monitor, spawn(fun monitor:loop/0)),
monitor ! new.](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-72-320.jpg)
![[De]constructing lists
user=> (first '(1 2 3 4))
1
user=> (rest '(1 2 3 4))
(2 3 4)
user=> (last '(1 2 3 4))
4
user=> (cons 0 '(1 2 3 4))
(0 1 2 3 4)](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-83-320.jpg)
![Vectors for ordered data
user=> (count [:foo :bar :baz])
3
user=> (first [:foo :bar :baz])
:foo
user=> (rest [:foo :bar :baz])
(:bar :baz)
user=> (last [:foo :bar :baz])
:baz
user=> (nth [:foo :bar :baz] 1)
:bar
user=> ([:foo :bar :baz] 1)
:bar](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-84-320.jpg)
![Defining functions
user=> (defn answer [] 42)
#'user/answer
user=> (answer)
42
user=> (defn treble [a] (* 3 a))
#'user/treble
user=> (treble 20)
60](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-87-320.jpg)
![Destructuring params
user=> (def board [[:x :o :x] [:o :x :o] [:o :x :o]])
#'user/board
user=> (defn centre [[_ [_ c _] _]] c)
#'user/centre
user=> (centre board)
:x
user=>(defn centre [[_ [_ c]]] c)
#'user/centre
user=>(defn centre [board]
(let [[_ [_ c]] board] c))
#'user/centre](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-88-320.jpg)
![Anonymous functions
user=> (defn treble [a] (* 3 a))
#'user/treble
user=> (def numbers [1 2 3])
#'user/numbers
user=> (map treble numbers)
(3 6 9)
user=> (map (fn [n] (* 3 n)) numbers)
(3 6 9)
user=> (map #(* 3 %) numbers)
(3 6 9)](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-89-320.jpg)
![Recursion: loop & recur
user=> (defn size [v]
(if (empty? v)
0
(inc (size (rest v)))))
#'user/size
user=> (size [1 2 3])
3
user=> (defn size [v]
(loop [l v, c 0]
(if (empty? l)
c
(recur (rest l) (inc c)))))](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-90-320.jpg)
![Working with sequences
user=> (def numbers [1 2 3 4])
#'user/numbers
user=> (every? odd? numbers)
false
user=> (filter odd? numbers)
(1 3)
user=> (for [x numbers] (* 2 x))
(2 4 6 8)
user=> (for [x numbers, y numbers] (* x y))
(1 2 3 4 2 4 6 8 3 6 9 12 4 8 12 16)
user=> (for [x numbers, y numbers, :when (odd? x)]
(* x y))
(1 2 3 4 3 6 9 12)](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-91-320.jpg)
![Lazy evaluation
user=> (take 5 (cycle ["I" "am" "what"]))
("I" "am" "what" "I" "am")
user=> (take 5 (drop 2 (cycle [1 2 3])))
(3 1 2 3 1)
user=> (->> [1 2 3] (cycle) (drop 2) (take 5))
(3 1 2 3 1)
user=> (take 5 (iterate inc 1))
(1 2 3 4 5)
user=> (defn factorial [n]
(apply * (take n (iterate inc 1))))
#'user/factorial
user=> (factorial 5)
120](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-92-320.jpg)
![Records & protocols
user=> (defprotocol Shape
(area [this]))
Shape
user=> (defrecord Square [width height]
Shape
(area [this] (* width height)))
user.Square
user=> (defrecord Circle [radius]
Shape
(area [this] (* (. Math PI) (* radius radius))))
user.Circle
user=> (area (Square. 2 3))
6
user=> (area (Circle. 4))
50.26548245743669](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-93-320.jpg)
![Macro expansion
user=> (defn unless [test body] (if (not test) body))
#'user/unless
user=> (unless true (println "It's a lie!"))
It's a lie!
nil](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-94-320.jpg)
![Macro expansion
user=> (defn unless [test body] (if (not test) body))
#'user/unless
user=> (unless true (println "It's a lie!"))
It's a lie!
nil
user=> (defmacro unless [test body]
(list 'if (list 'not test) body))
#'user/unless
user=> (macroexpand '(unless condition body))
(if (not condition) body)
user=> (unless true (println "It's a lie!"))
nil
user=> (unless false (println "It's true!"))
It's true!
nil](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-96-320.jpg)
![Encapsulation with atoms
user=> (def numbers (atom [1 2 3]))
#'user/numbers
user=> numbers
#<Atom@7d98d9cf: [1 2 3]>
user=> @numbers
[1 2 3]
user=> (reset! numbers [4 5 6])
[4 5 6]
user=> (swap! numbers conj 7)
[4 5 6 7]](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-98-320.jpg)
![Agents in the background
user=> (defn slow-twice [x]
(do (Thread/sleep 5000) (* 2 x)))
#'user/slow-twice
user=> (def number (agent 2))
#'user/number
user=> number
#<Agent@4c825cf3: 2>
user=> @number
2
user=> (send number slow-twice)
#<Agent@4c825cf3: 2>
user=> @number
2
user=> @number
4](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-99-320.jpg)
![The basics
Prelude> 2 + 2
4
Prelude> 2.0 * 2
4.0
Prelude> "foo" ++ "bar"
"foobar"
Prelude> ['h', 'e', 'l', 'l', 'o']
"hello"
Prelude> 2 > 1
True
Prelude> if (2 > 1) then "yes" else "no"
"yes"](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-104-320.jpg)
![Type inference
Prelude> :set +t
Prelude> 42
42
it :: Integer
Prelude> "Hello"
"Hello"
it :: [Char]
Prelude> 2 == 2
True
it :: Bool
Prelude> 1/2
0.5
it :: Double](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-105-320.jpg)
![Specifying function types
module Main where
double :: Integer -> Integer
double x = 2 * x
Prelude> :load main
[1 of 1] Compiling Main ( main.hs, interpreted )
Ok, modules loaded: Main.
*Main> double 2
4](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-107-320.jpg)
![Tuples & lists
Prelude> let (x, y) = (1, 2)
Prelude> x
1
Prelude> y
2
Prelude> let (head:tail) = [1, 2, 3, 4]
Prelude> head
1
Prelude> tail
[2,3,4]
Prelude> 1:[2, 3]
[1,2,3]
Prelude> [1, "two"]
<interactive>:1:2:
No instance for (Num [Char])
arising from the literal `1'](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-109-320.jpg)
![Ranges and sequences
Prelude> [1..5]
[1,2,3,4,5]
Prelude> [2, 4 .. 10]
[2,4,6,8,10]
Prelude> [0, 0.5 .. 2]
[0.0,0.5,1.0,1.5,2.0]
Prelude> take 5 [1 ..]
[1,2,3,4,5]](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-110-320.jpg)
![List comprehensions
Prelude> let numbers = [1,2,3]
Prelude> [x * 2 | x <- [1, 2, 3]]
[2,4,6]
Prelude> [[x, y] | x <- numbers, y <- numbers]
[[1,1],[1,2],[1,3],[2,1],[2,2],[2,3],[3,1],[3,2],[3,3]]
Prelude> [[x, y] | x <- numbers, y <- numbers, x < y]
[[1,2],[1,3],[2,3]]
Prelude> let more_numbers = [4,5]
Prelude> [(x, y, x * y) | x <- numbers, y <- more_numbers, x < y]
[(1,4,4),(1,5,5),(2,4,8),(2,5,10),(3,4,12),(3,5,15)]](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-111-320.jpg)
![Higher order functions
Prelude> (x -> 2 * x) 5
10
Prelude> map (x -> 2 * x) [1, 2, 3]
[2,4,6]
Prelude> map (* 2) [1, 2, 3]
[2,4,6]
Prelude> filter odd [1, 2, 3, 4]
[1,3]
Prelude> foldl (+) 0 [1, 2, 3, 4]
10](https://image.slidesharecdn.com/7li7w-120512024505-phpapp02/85/What-I-learned-from-Seven-Languages-in-Seven-Weeks-IPRUG-113-320.jpg)
![User-defined types
module Main where
data Tree a = Children [Tree a] | Leaf a
deriving (Show)
depth (Leaf _) = 1
depth (Children c) = 1 + maximum (map depth c)
*Main> let tree = Children[Leaf 1, Children [Leaf 2, Leaf 3]]
*Main> let x(Children [left, right]) = tree
*Main> left
Leaf 1
*Main> right
Children [Leaf 2,Leaf 3]
*Main> depth left
1
*Main> depth right
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What I learned from Seven Languages in Seven Weeks (IPRUG)
- 1. What I learned from Seven Languages in Seven Weeks Kerry Buckley (@kerryb) – IPRUG 1/5/12
- 3. Twenty-
- 7. What is the typing model? What is the programming model? How will you interact with it? What are the decision constructs and core data structures? What are the core features that make the language unique?
- 8. Java was like having a rich lawyer as a brother. He was fun when he was younger, but now he’s a black hole that sucks away all the joy in a 100-mile radius.
- 10. Meet Ruby, one of my favorites. She’s sometimes quirky, always beautiful, a little mysterious, and absolutely magical.
- 12. Pros Power and flexibility Developer productivity and fun Raw execution speed Limited concurrency support Type-aware tool support Cons
- 14. Io is a rule bender. He’s young, wicked smart, and easy to understand but hard to predict. He might give you the ride of your life, wreck your dad’s car, or both.
- 15. Message passing Io> "oI olleH" reverse ==> Hello Io Io> list("oI", "iH") map(reverse) ==> list(Hi, Io) Io> list(1, 2, 3) map(** 2) sum ==> 14
- 16. Objects and Slots Io> Person := Object clone ==> Person_0x7f922c06ad00: type = "Person" Io> Person firstName := "John" ==> John Io> Person lastName := "Doe" ==> Doe Io> Person firstName ==> John
- 17. Defining methods Io> Person name := method ( firstName .. " " .. lastName ) Io> Person name ==> John Doe
- 18. Prototype inheritance Io> Kerry := Person clone ==> Kerry_0x7f922c0e0220: type = "Kerry" Io> Kerry name ==> John Doe Io> Kerry firstName = "Kerry" Io> Kerry lastName = "Buckley" Io> Kerry name ==> Kerry Buckley
- 19. Control structures Io> for(i, 1, 3, i println) 1 2 3 ==> 3 Io> if(true, "Yes" println, "No" println) Yes ==> Yes
- 20. Adding operators Io> true xor := method(x, if(x, false, true)) Io> false xor := method(x, if(x, true, false)) Io> OperatorTable addOperator("xor", 11) ==> OperatorTable_0x105972e00: Operators 0 ? @ @@ 1 ** 2 % * / 3 + - ... 11 or xor || ...
- 21. Reflection Io> foo := method( call sender println call message arguments println ) Io> foo("bar", 42) Object_0x7fcf78418920: Lobby = Object_0x7fcf78418920 Protos = Object_0x7fcf78417c00 ... list("bar", 42)
- 22. Coroutines Io> Ping := Object clone Io> Pong := Object clone Io> Ping ping := method ( 2 repeat("Ping!" println; yield)) Io> Pong pong := method ( 2 repeat(yield; "Pong!" println)) Io> Ping @@ping; Pong @@pong Io> Coroutine currentCoroutine pause Ping! Pong! Ping! Pong!
- 23. Actors Io> Slow := Object clone Io> Fast := Object clone Io> Slow go := method( wait(1) "Slow" println ) Io> Fast go := method( "Fast" println ) Io> Slow @@go; Fast @@go; wait(2) Fast Slow
- 24. Futures Io> page := URL with( "http://iprug.org/") @fetch Io> # do other things while waiting Io> page size println # blocks until ready 91559
- 25. Pros Tiny – ideal for embedded systems Prototypes and duck typing are very flexible Concurrency support Simple, consistent syntax Raw execution speed Small user community Cons
- 27. Sometimes spectacularly smart, other times just as frustrating. You’ll get astounding answers only if you know how to ask the question.
- 28. Simple facts likes(wallace, cheese). likes(gromit, cheese). likes(wendolene, sheep). ?- likes(wallace, sheep). false. ?- likes(gromit, cheese). true. ?- likes(Who, cheese). Who = wallace ; Who = grommit.
- 29. Evaluating rules friend(X, Y) :- +(X = Y), likes(X, Z), likes(Y, Z). ?- friend(wallace, wallace). false. ?- friend(wendolene, gromit). false. ?- friend(wallace, gromit). true.
- 30. Recursive rules father(grandpa, homer). father(homer, bart). ancestor(X, Y) :- father(X, Y). ancestor(X, Y) :- father(X, Z), ancestor(Z, Y). ?- ancestor(Who, bart). Who = homer ; Who = grandpa ; false.
- 31. Tuples ?- (X, Y, Z) = (1, 2, "foo"). X = 1, Y = 2, Z = [102, 111, 111]. ?- (X, _, Z) = (1, 2, "foo"). X = 1, Z = [102, 111, 111].
- 32. Calculation with lists sum(0, []). sum(Total, [Head|Tail]) :- sum(Sum, Tail), Total is Head + Sum. ?- sum(What, [1, 2, 3]). What = 6.
- 33. Solving (4×4) sudoku ?- sudoku([_, _, 2, 3, _, _, _, _, _, _, _, _, 3, 4, _, _], Solution). Solution = [4,1,2,3,2,3,4,1,1,2,3,4,3,4,1,2].
- 34. Solving (4×4) sudoku valid([]). valid([Head|Tail]) :- all_different(Head), valid(Tail). sudoku(Puzzle, Solution) :- Solution = Puzzle, Puzzle = [S11, S12, S13, S14, S21, S22, S23, S24, S31, S32, S33, S34, S41, S42, S43, S44], Solution ins 1..4, Row1 = [S11, S12, S13, S14], Row2 = [S21, S22, S23, S24], Row3 = [S31, S32, S33, S34], Row4 = [S41, S42, S43, S44], Col1 = [S11, S21, S31, S41], Col2 = [S12, S22, S32, S42], Col3 = [S13, S23, S33, S43], Col4 = [S14, S24, S34, S44], Square1 = [S11, S12, S21, S22], Square2 = [S13, S14, S23, S24], Square3 = [S31, S32, S41, S42], Square4 = [S33, S34, S43, S44], valid([Row1, Row2, Row3, Row4, Col1, Col2, Col3, Col4, Square1, Square2, Square3, Square4]).
- 35. YOU DESCRIBE THE PROBLEM PROLOG WORKS OUT THE ANSWER
- 36. Pros Solving logical and scheduling problems Natural language processing Artificial intelligence Scaling requires deep understanding Not a general-purpose language Simple procedural tasks are difficult Cons
- 38. He was often awkward, was sometimes amazing, but always had a unique expression. Sometimes, his scissors let him do incredible things. Other times, he was awkward and humiliated.
- 39. Type inference & coercion scala> "foo" res0: java.lang.String = foo scala> 123 res1: Int = 123 scala> 45.6 res2: Double = 45.6 scala> 1 + 2.3 res3: Double = 3.3 scala> "The answer is " + 42 res4: java.lang.String = The answer is 42
- 40. var and val scala> var a = 42 a: Int = 42 scala> a = 69 a: Int = 69 scala> val b = 999 b: Int = 999 scala> b = 911 <console>:8: error: reassignment to val b = 911 ^
- 41. Ranges and tuples scala> val range = 0 to 3 range: scala.collection.immutable.Range.Inclusive = Range(0, 1, 2, 3) scala> val range = 0 to 5 by 2 range: scala.collection.immutable.Range = Range(0, 2, 4) scala> val tuple = ("Kerry", 42) tuple: (java.lang.String, Int) = (Kerry,42) scala> val (name, age) = tuple name: java.lang.String = Kerry age: Int = 42
- 42. Defining classes class Person(firstName: String, lastName: String) { def greet(name: String) { println("Hello " + name + ", I'm " + firstName + ".") } } scala> val kerry = new Person("Kerry", "Buckley") kerry: Person = Person@276bab54 scala> kerry.greet("IPRUG") Hello IPRUG, I'm Kerry.
- 43. Objects & Class Methods object Highlander { def copy { println("There can be only one!") } } scala> Highlander.copy There can be only one!
- 44. Extending & traits class Person(val name:String) trait Nice { def greet() = println("Howdily doodily.") } class Character(override val name:String) extends Person(name) with Nice scala> val flanders = new Character("Ned") scala> flanders.greet Howdily doodily.
- 45. Lists, sets & maps scala> val list = List("one", "two", 3) list: List[Any] = List(one, two, 3) scala> list(1) res0: Any = two scala> Set(1, 2, 3) ++ Set(2, 3, 4) res1: scala.collection.immutable.Set[Int] = Set(1, 2, 3, 4) scala> val map = Map(1 -> "One", 2 -> "Two") map: scala.collection.immutable.Map[Int,java.lang.String] = Map(1 -> One, 2 -> Two) scala> map(1) res2: java.lang.String = One
- 46. Heads and tails scala> val list = List("one", "two", "three") list: List[java.lang.String] = List(one, two, three) scala> list.head res0: java.lang.String = one scala> list.tail res1: List[java.lang.String] = List(two, three) scala> list.init res2: List[java.lang.String] = List(one, two) scala> list.last res3: java.lang.String = three
- 47. List processing scala> val jedi = List("Yoda", "Obiwan", "Luke") jedi: List[java.lang.String] = List(Yoda, Obiwan, Luke) scala> jedi.filter(name => name.size < 5) res0: List[java.lang.String] = List(Yoda, Luke) scala> jedi.map(name => name.size) res1: List[Int] = List(4, 6, 4) scala> val numbers = List(1, 2, 3) numbers: List[Int] = List(1, 2, 3) scala> numbers.foldLeft(0)((a, n) => a + n) res2: Int = 6
- 48. Class hierarchy Any AnyVal AnyRef Float Int … ScalaObject … List Map Nothing Null
- 49. First-class XML scala> val pets = <pets> <chicken>Babs</chicken> <chicken>Bunty</chicken> <chicken>Lily</chicken> <cat>Pebbles</cat> <chicken>Pepper</chicken> <cat>Twiglet</cat> <cat>Willow</cat> <cat>Zorro</cat> </pets> scala> pets "cat" res0: scala.xml.NodeSeq = NodeSeq(<cat>Twiglet</cat>, <cat>Pebbles</cat>, <cat>Willow</cat>, <cat>Zorro</cat>)
- 50. YO DAWG, I HEARD YOU LIKE XML SO I PUT SOME XML IN YOUR SCALA
- 51. Pattern matching scala> (pets "_").foreach {pet => pet match { case <cat>{name}</cat> => println(name + " says 'meow'.") case <chicken>{name}</chicken> = println(name + " says 'cluck'.") } } Babs says 'cluck'. Bunty says 'cluck'. Lily says 'cluck'. Pebbles says 'meow'. Pepper says 'cluck'. Twiglet says 'meow'. Willow says 'meow'. Zorro says 'meow'.
- 52. Concurrency with actors case object Stroke case object Feed class Cat() extends Actor { def act() { loop { react { case Stroke => { println("Purr!") } case Feed => { println("Om nom nom") } } } } } scala> val cat = new Cat().start scala> cat ! Stroke; cat ! Feed; println("Done.") Done. Purr! Om nom nom
- 53. Pros A modern version of Java Mixins, pattern matching, blocks, XML Concurrency with actors & immutability Static typing Compromises with mutable state Cons
- 55. Agent Smith was an artificial intelligence program in the matrix that had an amazing ability to take any form and bend the rules of reality to be in many places at once. He was unavoidable.
- 56. The usual types (mostly) 1> 2 + 2. 4 2> "Hello". "Hello" 3> atom. atom 4> {foo, 123, "bar"}. {foo,123,"bar"} 5> [1, "one", two]. [1,"one", two] 6> [87, 84, 70, 63]. "WTF?"
- 57. Variables don’t change 1> Foo = 123. 123 2> Foo. 123 3> Bar = 456. 456 4> Foo + Bar. 579 5> Foo = 1. ** exception error: no match of right hand side value 1
- 58. Pattern matching 1> Pet = {{name, "Zorro"}, {type, "Cat"}}. {{name,"Zorro"},{type,"Cat"}} 2> {{name, Name}, {type, Type}} = Pet. {{name,"Zorro"},{type,"Cat"}} 3> Name. "Zorro" 4> Type. "Cat" 5> [Head|Tail] = [foo, bar, baz]. [foo,bar,baz] 6> {Head, Tail}. {foo,[bar,baz]}
- 59. Bit matching 1> [A, B, C, D] = [1, 0, 50, 200]. [1,0,50,200] 2> Packed = <<A:1, B:1, C:6, D:8>>. <<"²È">> 3> <<P:1, Q:1, R:6, S:8>> = Packed. <<"²È">> 4> {P, Q, R, S}. {1,0,50,200}
- 60. Basic functions -module(demo). -export([echo/1]). echo(Anything) -> Anything. 1> c(demo). {ok,demo} 5> demo:echo("Hello"). "Hello" 6> demo:echo(42). 42
- 61. Patterns in functions -module(fact). -export([fact/1]). fact(0) -> 1; fact(N) -> N * fact(N-1). 1> c(fact). {ok,fact} 3> fact:fact(6). 720 4> fact:fact("foo"). ** exception error: bad argument in an arithmetic expression in function fact:fact/1 (fact.erl, line 5) 6> fact:fact(10000).
- 65. Control structures 1> List = [1, 2, 3]. [1,2,3] 2> case List of 2> [] -> none; 2> [_|[]] -> one; 2> _ -> some 2> end. some 3> A = 42. 42 4> if 4> A < 10 -> small; 4> A < 100 -> big; 4> true -> massive 4> end. big
- 66. Higher order functions 1> Double = fun(X) -> X * 2 end. #Fun<erl_eval.6.111823515> 2> Double(2). 4 3> List = [1, 2, 3]. [1,2,3] 4> lists:map(Double, List). [2,4,6] 5> lists:map(fun(X) -> X + 1 end, List). [2,3,4] 6> lists:foldl(fun(X, Sum) -> X + Sum end, 0, List). 6
- 67. Building lists -module(double). -export([double_all/1]). double_all([]) -> []; double_all([H|T]) -> [H * 2|double_all(T)]. 1> c(double). {ok,double} 2> double:double_all([1, 2, 3, 4]). [2,4,6,8]
- 68. List comprehensions 1> Numbers = [1, 2, 3, 4]. [1,2,3,4] 2> Double = fun(X) -> X * 2 end. #Fun<erl_eval.6.111823515> 3> lists:map(Double, Numbers). [2,4,6,8] 4> [Double(X) || X <- Numbers]. [2,4,6,8] 5> [X || X <- Numbers, X > 1, X < 4]. [2,3] 6> Basket = [{pencil, 4, 0.25}, {pen, 1, 1.20}, {paper, 2, 1.00}]. [{pencil,4,0.25},{pen,1,1.2},{paper,2,1.0}] 7> Totals = [{Item, Qty * Price} || {Item, Qty, Price} <- Basket]. [{pencil,1.0},{pen,1.2},{paper,2.0}]
- 70. Message loops -module(doubler). -export([loop/0]). loop() -> receive N -> io:format("~b~n", [N * 2]), loop() end. 18> Doubler = spawn(fun doubler:loop/0). <0.87.0> 19> Doubler ! 2. 4 2
- 71. Synchronous messages -module(doubler). -export([loop/0, double/2]). loop() -> receive {Pid, N} -> Pid ! (N * 2), loop() end. double(To, N) -> To ! {self(), N}, receive Result -> Result end. 27> Doubler = spawn(fun doubler:loop/0). <0.118.0> 28> doubler:double(Doubler, 3). 6
- 72. Monitor and restart -module(monitor). -export([loop/0, start/0]). loop() -> process_flag(trap_exit, true), receive new -> register(doubler, spawn_link(fun doubler:loop/0)), loop(); {'EXIT', From, Reason} -> io:format("~p exited: ~p.", [From, Reason]), monitor ! new, loop() end. start() -> register(monitor, spawn(fun monitor:loop/0)), monitor ! new.
- 73. Pros Designed for concurrency & fault tolerance Flexibility of dynamic typing Lightweight processes with message passing & monitoring Build scalable applications with the OTP library Syntax sometimes a little clumsy Integration with other languages Cons
- 75. His communication style is often inverted and hard to understand. He seems too small to make a difference, but it quickly becomes apparent that there is more to Yoda than meets the eye.
- 76. Prefix notation user=> (+ 2 2) 4 user=> (- 10 4 1) 5 user=> (/ 2.0 3) 0.6666666666666666 user=> (/ 2 3) 2/3 user=> (count "hello") 5 user=> (+ (count "hello") (count "clojure")) 12
- 77. Strings & chars user=> (println "foontbar") foo bar nil user=> (str 123) "123" user=> (str "hello " "world") "hello world" user=> (str "foo" "bar" 42 b a z) "foobar42baz"
- 78. Java hiding underneath user=> (class 1) java.lang.Integer user=> (class "foo") java.lang.String user=> (class (= 2 2)) java.lang.Boolean user=> (class (/ 1 2)) clojure.lang.Ratio
- 79. if is a function user=> (if (> 2 1) (println "yes")) yes nil user=> (if (= (count "foo") 2) (println "yes") (println "no")) no nil
- 80. Functions are lists user=> (1 2 3) java.lang.ClassCastException: java.lang.Integer cannot be cast to clojure.lang.IFn (NO_SOURCE_FILE:0)
- 81. I TYPE LIST Y U NO PARSE AS LIST?
- 82. Functions are lists user=> (1 2 3) java.lang.ClassCastException: java.lang.Integer cannot be cast to clojure.lang.IFn (NO_SOURCE_FILE:0) user=> (list 1 2 3) (1 2 3) user=> (class (list 1 2 3)) clojure.lang.PersistentList user=> '(1 2 3) (1 2 3) user=> (class '(+ 2 2)) clojure.lang.PersistentList user=> (eval '(+ 2 2)) 4
- 83. [De]constructing lists user=> (first '(1 2 3 4)) 1 user=> (rest '(1 2 3 4)) (2 3 4) user=> (last '(1 2 3 4)) 4 user=> (cons 0 '(1 2 3 4)) (0 1 2 3 4)
- 84. Vectors for ordered data user=> (count [:foo :bar :baz]) 3 user=> (first [:foo :bar :baz]) :foo user=> (rest [:foo :bar :baz]) (:bar :baz) user=> (last [:foo :bar :baz]) :baz user=> (nth [:foo :bar :baz] 1) :bar user=> ([:foo :bar :baz] 1) :bar
- 85. Sets for unordered data user=> (def fruit #{:apple :orange :banana}) #'user/fruit user=> fruit #{:orange :apple :banana} user=> (count fruit) 3 user=> (sort fruit) (:apple :banana :orange) user=> (clojure.set/union fruit #{:pear :plum}) #{:plum :orange :pear :apple :banana} user=> (fruit :apple) :apple user=> (fruit :pizza) nil
- 86. Maps for key/value pairs user=> (def myMap {:foo 1, :bar 2, :baz 3}) #'user/myMap user=> (myMap :foo) 1 user=> (:foo myMap) 1 user=> (merge myMap {:quz 4}) {:quz 4, :foo 1, :bar 2, :baz 3} user=> (merge-with + myMap {:bar 10, :quz 4}) {:quz 4, :foo 1, :bar 12, :baz 3}
- 87. Defining functions user=> (defn answer [] 42) #'user/answer user=> (answer) 42 user=> (defn treble [a] (* 3 a)) #'user/treble user=> (treble 20) 60
- 88. Destructuring params user=> (def board [[:x :o :x] [:o :x :o] [:o :x :o]]) #'user/board user=> (defn centre [[_ [_ c _] _]] c) #'user/centre user=> (centre board) :x user=>(defn centre [[_ [_ c]]] c) #'user/centre user=>(defn centre [board] (let [[_ [_ c]] board] c)) #'user/centre
- 89. Anonymous functions user=> (defn treble [a] (* 3 a)) #'user/treble user=> (def numbers [1 2 3]) #'user/numbers user=> (map treble numbers) (3 6 9) user=> (map (fn [n] (* 3 n)) numbers) (3 6 9) user=> (map #(* 3 %) numbers) (3 6 9)
- 90. Recursion: loop & recur user=> (defn size [v] (if (empty? v) 0 (inc (size (rest v))))) #'user/size user=> (size [1 2 3]) 3 user=> (defn size [v] (loop [l v, c 0] (if (empty? l) c (recur (rest l) (inc c)))))
- 91. Working with sequences user=> (def numbers [1 2 3 4]) #'user/numbers user=> (every? odd? numbers) false user=> (filter odd? numbers) (1 3) user=> (for [x numbers] (* 2 x)) (2 4 6 8) user=> (for [x numbers, y numbers] (* x y)) (1 2 3 4 2 4 6 8 3 6 9 12 4 8 12 16) user=> (for [x numbers, y numbers, :when (odd? x)] (* x y)) (1 2 3 4 3 6 9 12)
- 92. Lazy evaluation user=> (take 5 (cycle ["I" "am" "what"])) ("I" "am" "what" "I" "am") user=> (take 5 (drop 2 (cycle [1 2 3]))) (3 1 2 3 1) user=> (->> [1 2 3] (cycle) (drop 2) (take 5)) (3 1 2 3 1) user=> (take 5 (iterate inc 1)) (1 2 3 4 5) user=> (defn factorial [n] (apply * (take n (iterate inc 1)))) #'user/factorial user=> (factorial 5) 120
- 93. Records & protocols user=> (defprotocol Shape (area [this])) Shape user=> (defrecord Square [width height] Shape (area [this] (* width height))) user.Square user=> (defrecord Circle [radius] Shape (area [this] (* (. Math PI) (* radius radius)))) user.Circle user=> (area (Square. 2 3)) 6 user=> (area (Circle. 4)) 50.26548245743669
- 94. Macro expansion user=> (defn unless [test body] (if (not test) body)) #'user/unless user=> (unless true (println "It's a lie!")) It's a lie! nil
- 96. Macro expansion user=> (defn unless [test body] (if (not test) body)) #'user/unless user=> (unless true (println "It's a lie!")) It's a lie! nil user=> (defmacro unless [test body] (list 'if (list 'not test) body)) #'user/unless user=> (macroexpand '(unless condition body)) (if (not condition) body) user=> (unless true (println "It's a lie!")) nil user=> (unless false (println "It's true!")) It's true! nil
- 97. Transactional memory user=> (def kerry (ref "Kerry")) #'user/kerry user=> (deref kerry) "Kerry" user=> (alter kerry str " Buckley") java.lang.IllegalStateException: No transaction running (NO_SOURCE_FILE:0) user=> (dosync (alter kerry str " Buckley")) "Kerry Buckley"
- 98. Encapsulation with atoms user=> (def numbers (atom [1 2 3])) #'user/numbers user=> numbers #<Atom@7d98d9cf: [1 2 3]> user=> @numbers [1 2 3] user=> (reset! numbers [4 5 6]) [4 5 6] user=> (swap! numbers conj 7) [4 5 6 7]
- 99. Agents in the background user=> (defn slow-twice [x] (do (Thread/sleep 5000) (* 2 x))) #'user/slow-twice user=> (def number (agent 2)) #'user/number user=> number #<Agent@4c825cf3: 2> user=> @number 2 user=> (send number slow-twice) #<Agent@4c825cf3: 2> user=> @number 2 user=> @number 4
- 100. Back to the futures user=> (def ultimate-answer (future (do (Thread/sleep 2.4e17) 42))) #'user/ultimate-answer user=> @ultimate-answer 42
- 101. Pros A good lisp implementation Access to Java ecosystem Concurrency provided by STM Prefix notation can be confusing (((((and all those parens don’t help))))) Some limitations compared to other lisps Cons
- 103. Haskell represents purity and freedom, but the power comes at a price. Think Spock from Star Trek. His character has a single-minded purity that has endeared him to generations.
- 104. The basics Prelude> 2 + 2 4 Prelude> 2.0 * 2 4.0 Prelude> "foo" ++ "bar" "foobar" Prelude> ['h', 'e', 'l', 'l', 'o'] "hello" Prelude> 2 > 1 True Prelude> if (2 > 1) then "yes" else "no" "yes"
- 105. Type inference Prelude> :set +t Prelude> 42 42 it :: Integer Prelude> "Hello" "Hello" it :: [Char] Prelude> 2 == 2 True it :: Bool Prelude> 1/2 0.5 it :: Double
- 106. Defining functions Prelude> let double x = x * 2 double :: Num a => a -> a Prelude> double 4 8 Prelude> let times x y = x * y times :: Num a => a -> a -> a Prelude> times 5 6 30
- 107. Specifying function types module Main where double :: Integer -> Integer double x = 2 * x Prelude> :load main [1 of 1] Compiling Main ( main.hs, interpreted ) Ok, modules loaded: Main. *Main> double 2 4
- 108. Pattern matching & guards module Main where factorial :: Integer -> Integer factorial 0 = 1 factorial x = x * factorial (x - 1) factorial2 :: Integer -> Integer factorial2 x | x > 1 = x * factorial2 (x - 1) | otherwise = 1
- 109. Tuples & lists Prelude> let (x, y) = (1, 2) Prelude> x 1 Prelude> y 2 Prelude> let (head:tail) = [1, 2, 3, 4] Prelude> head 1 Prelude> tail [2,3,4] Prelude> 1:[2, 3] [1,2,3] Prelude> [1, "two"] <interactive>:1:2: No instance for (Num [Char]) arising from the literal `1'
- 110. Ranges and sequences Prelude> [1..5] [1,2,3,4,5] Prelude> [2, 4 .. 10] [2,4,6,8,10] Prelude> [0, 0.5 .. 2] [0.0,0.5,1.0,1.5,2.0] Prelude> take 5 [1 ..] [1,2,3,4,5]
- 111. List comprehensions Prelude> let numbers = [1,2,3] Prelude> [x * 2 | x <- [1, 2, 3]] [2,4,6] Prelude> [[x, y] | x <- numbers, y <- numbers] [[1,1],[1,2],[1,3],[2,1],[2,2],[2,3],[3,1],[3,2],[3,3]] Prelude> [[x, y] | x <- numbers, y <- numbers, x < y] [[1,2],[1,3],[2,3]] Prelude> let more_numbers = [4,5] Prelude> [(x, y, x * y) | x <- numbers, y <- more_numbers, x < y] [(1,4,4),(1,5,5),(2,4,8),(2,5,10),(3,4,12),(3,5,15)]
- 112. Function currying Prelude> 4 * 5 20 Prelude> (*) 4 5 20 Prelude> :t (*) (*) :: Num a => a -> a -> a Prelude> let double = (* 2) Prelude> :t double double :: Integer -> Integer Prelude> double 3 6
- 113. Higher order functions Prelude> (x -> 2 * x) 5 10 Prelude> map (x -> 2 * x) [1, 2, 3] [2,4,6] Prelude> map (* 2) [1, 2, 3] [2,4,6] Prelude> filter odd [1, 2, 3, 4] [1,3] Prelude> foldl (+) 0 [1, 2, 3, 4] 10
- 114. User-defined types module Main where data Tree a = Children [Tree a] | Leaf a deriving (Show) depth (Leaf _) = 1 depth (Children c) = 1 + maximum (map depth c) *Main> let tree = Children[Leaf 1, Children [Leaf 2, Leaf 3]] *Main> let x(Children [left, right]) = tree *Main> left Leaf 1 *Main> right Children [Leaf 2,Leaf 3] *Main> depth left 1 *Main> depth right 2
- 115. Type classes class Eq a where (==), (/=) :: a -> a -> Bool -- Minimal complete definition: -- x/=y x==y (==) or (/=) = not(x==y) = not(x/=y) *Main> :info Integer data Integer = integer-gmp:GHC.Integer.Type.S# GHC.Prim.Int# | integer-gmp:GHC.Integer.Type.J# GHC.Prim.Int# GHC.Prim.ByteArray# -- Defined in integer-gmp:GHC.Integer.Type instance Enum Integer -- Defined in GHC.Num instance Eq Integer -- Defined in GHC.Classes instance Integral Integer -- Defined in GHC.Real instance Num Integer -- Defined in GHC.Num instance Ord Integer -- Defined in GHC.Classes instance Read Integer -- Defined in GHC.Read instance Real Integer -- Defined in GHC.Real instance Show Integer -- Defined in GHC.Num
- 116. Monads A monad is a construction that, given an underlying type system, embeds a corresponding type system (called the monadic type system) into it (that is, each monadic type acts as the underlying type). This monadic type system preserves all significant aspects of the underlying type system, while adding features particular to the monad. Monads must obey the following rules: • (return x) >>= f ≡ f x • m >>= return ≡ m • (m >>= f) >>= g ≡ m >>= ( x -> (f x >>= g) )
- 118. The maybe monad data Maybe a = Nothing | Just a Prelude> case (html doc) of Nothing -> Nothing Just x -> case body x of Nothing -> Nothing Just y -> paragraph 2 y instance Monad Maybe where return = Just Nothing >>= f = Nothing (Just x) >>= f = f x Prelude> Just someWebPage >>= html >>= body >>= paragraph >>= return
- 119. Pros Pure functional language with no side effects Strong typing with powerful type inference Laziness reduces need for recursion Ideal for learning the functional paradigm Inflexibility and lack of compromise Small community outside academia Steep learning curve (especially monads!) Cons
- 120. What I learned from Seven Languages in Seven Weeks
- 121. Functional style def total_price(widgets) total = 0 widgets.each do |widget| if widget.red? total += widget.price end end total end def total_price(widgets) widgets.select{|w| w.red?}.map{|w| w.price}.reduce(&:+) end
- 122. JVM or standalone? • Access to Java libraries • Deployment environments • Escape route for Java developers • Limitations (eg tail recursion)
- 123. Know what’s out there • Languages • Features • First-class functions • List comprehensions • Pattern matching • Lazy evaluation
- 124. Dealing with concurrency • Immutability • Coroutines • Actors • Futures • Software Transactional Memory
- 125. SAYS HE’LL DO A QUICK TALK TURNS UP WITH 115 SLIDES