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![Arrays, ranges & hashes
>> array = [1, 2.0, "three"]
>> array[0]
=> 1
>> array.reverse
=> ["three", 2.0, 1]
>> range = (1..10)
>> range.include? 5
=> true
>> hash = {:foo => 123, "bar" => "", 456 => [1, 2]}
>> hash[456]
=> [1, 2]](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-13-320.jpg)
![Open classes
class NilClass
def blank?
true
end
end
class String
def blank?
empty?
end
end
>> [nil, "", "foo"].map &:blank?
=> [true, true, false]](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-15-320.jpg)
![Modules & mixins
module Debug
def info
"#{self.class}[#{object_id}]: #{to_s}"
end
end
class Object
include Debug
end
>> 2.info
=> "Fixnum[5]: 2"
>> "foo".info
=> "String[70107061928320]: foo"](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-16-320.jpg)
![Collections & Enumerable
class MyCollection
include Enumerable
def each
...
end
end
>> MyCollection.instance_methods.sort
=> [:all?, :any?, :chunk, :collect, :collect_concat,
:count, :cycle, :detect, :drop, :drop_while, :each,
:each_cons, :each_entry, :each_slice, :each_with_index,
:each_with_object, :entries, :find, :find_all, :find_index,
:first, :flat_map, :grep, :group_by, :include?, :inject,
:map, :max, :max_by, :member?, :min, :min_by, :minmax,
:minmax_by, :none?, :one?, :partition, :reduce, :reject,
:reverse_each, :select, :slice_before, :sort, :sort_by,
:take, :take_while, :to_a, :zip]](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-17-320.jpg)
![method_missing magic
class MyStruct
def initialize values
@values = values
end
def method_missing name, *args
@values[name]
end
end
>> struct = MyStruct.new foo: 123, bar: 456
=> #<MyStruct:0x007fc2c21433b8 @values={:foo=>123, :bar=>456}>
>> struct.foo
=> 123
>> struct.bar
=> 456](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-18-320.jpg)
![Dynamic definition
class MyStruct
def initialize values
@values = values
end
def method_missing name, *args
puts "Defining method #{name}"
self.class.class_eval do
define_method(name) { @values[name] }
end
send(name, *args)
end
end
>> struct.foo
Defining method foo
=> 123
>> struct.foo
=> 123](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-19-320.jpg)
![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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-38-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-39-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-40-320.jpg)
![Solving (4×4) sudoku
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]).
valid([]).
valid([Head|Tail]) :-
all_different(Head),
valid(Tail).](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-41-320.jpg)
![Lists, sets & maps
scala> val list = List(1, 2, 3)
list: List[Int] = List(1, 2, 3)
scala> list(1)
res0: Int = 2
scala> "zero"::list
res1: List[Any] = List(zero, 1, 2, 3)
scala> Set(1, 2, 3) ++ Set(2, 3, 4)
res2: 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)
res3: java.lang.String = One](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-48-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-52-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-60-320.jpg)
![Variables don’t change
1> Foo = 42.
42
2> Foo = Foo + 1.
** exception error: no match of right hand side value 43
3> Values = [1, 2, 3].
[1,2,3]
4> lists:append(Values, [4]).
[1,2,3,4]
5> Values.
[1,2,3]](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-61-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-62-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-63-320.jpg)
![Basic functions
-module(demo).
-export([echo/1]).
echo(Value) -> Value.
1> c(demo).
{ok,demo}
5> demo:echo("Hello").
"Hello"
6> demo:echo(42).
42](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-64-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-65-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-69-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-70-320.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](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-71-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-72-320.jpg)
![Monitor & 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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-73-320.jpg)
![Vectors, sets & maps
user=> (def numbers [1 2 3])
(1 2 3)
user=> (conj numbers "forty-two")
[1 2 3 "forty-two"]
user=> (def crew #{:zaphod :trillian :marvin})
#'user/crew
user=> (clojure.set/union crew #{:ford :zaphod :arthur})
#{:arthur :trillian :ford :zaphod :marvin}
user=> (def home {:arthur :earth, :ford :betelgeuse, :marvin :sirius})
#'user/home
user=> (home :arthur)
:earth
user=> (:arthur home)
:earth](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-80-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-81-320.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](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-82-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-83-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-84-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-85-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-86-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-87-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-88-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-90-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-91-320.jpg)
![Type inference
Prelude> :set +t
Prelude> 42
42
it :: Integer
Prelude> "Mostly harmless"
"Mostly harmless"
it :: [Char]
Prelude> "black" == "white"
False
it :: Bool
Prelude> 1/2
0.5
it :: Double](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-96-320.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
*Main> double 2.5
<interactive>:1:8:
No instance for (Fractional Integer)
arising from the literal `2.5'](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-98-320.jpg)
![Tuples & lists
Prelude> let zaphod = ("Zaphod", "Beeblebrox", "Betelgeuse", 2)
Prelude> let (_, _, _, numberOfHeads) = zaphod
Prelude> let numbers = [1, 2, 3, 4]
Prelude> let (head:tail) = numbers
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'
Possible fix: add an instance declaration for (Num [Char])
In the expression: 1
In the expression: [1, "two"]
In an equation for `it': it = [1, "two"]](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-100-320.jpg)
![Ranges & 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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-101-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-102-320.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-devcon5-120530045511-phpapp01/85/7li7w-devcon5-104-320.jpg)
![User-defined types
module Main where
data Shape = Circle Float | Rectangle Float Float
deriving show
area :: Shape -> Float
area (Circle r) = pi * r ^ 2
area (Rectangle x y) = x * y
*Main> let circle = Circle 10
*Main> let rect = Rectangle 6 7
*Main> area circle
314.15927
*Main> area rect
42.0
*Main> [circle, rect]
[Circle 10.0,Rectangle 6.0 7.0]](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-106-320.jpg)
![Record syntax
module Main where
data Shape = Circle {radius :: Float}
| Rectangle {width :: Float, height :: Float}
deriving Show
area :: Shape -> Float
area (Circle r) = pi * r ^ 2
area (Rectangle x y) = x * y
*Main> let circle = Circle 10
*Main> let rect = Rectangle 6 7
*Main> [circle, rect]
[Circle {radius = 10.0},Rectangle {width = 6.0, height = 7.0}]](https://image.slidesharecdn.com/7li7w-devcon5-120530045511-phpapp01/85/7li7w-devcon5-107-320.jpg)
Uploaded byKerry Buckley
7li7w devcon5
The document discusses learning various programming languages, highlighting their unique features and concepts such as typing models, concurrency, and collection handling. It covers languages like Ruby, Prolog, Scala, Erlang, Clojure, and Haskell, emphasizing their strengths, weaknesses, and practical examples. The author reflects on the experiences and insights gained from mastering these languages in a condensed format.
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- 8.
- 9. Meet Ruby, oneof my favorites. She’s sometimes quirky, always beautiful, a little mysterious, and absolutely magical.
- 10. The irb console >>puts "Hello world" Hello world => nil >> name = "Kerry" => "Kerry" >> puts "Hello #{name}" Hello Kerry => nil
- 11. Everything’s an object >>42.class => Fixnum >> nil.class => NilClass >> String.class => Class > 42.methods => [:to_s, :+, :-, :*, :/, :abs, ...
- 12. Duck typing def double(x) x * 2 end >> double(2) => 4 >> double(2.5) => 5.0 >> double("foo") => "foofoo" >> double(false) NoMethodError: undefined method `*' for false:FalseClass from (irb):2:in `double'
- 13. Arrays, ranges &hashes >> array = [1, 2.0, "three"] >> array[0] => 1 >> array.reverse => ["three", 2.0, 1] >> range = (1..10) >> range.include? 5 => true >> hash = {:foo => 123, "bar" => "", 456 => [1, 2]} >> hash[456] => [1, 2]
- 14. Blocks & yield >>3.times { puts "hello" } hello hello hello >> File.open "some-file", "w" do |f| ?> f.write "some-data" >> end >> def delayed_by seconds >> sleep seconds >> yield >> end >> delayed_by 5 do ?> puts "At last!" >> end At last!
- 15. Open classes class NilClass def blank? true end end class String def blank? empty? end end >> [nil, "", "foo"].map &:blank? => [true, true, false]
- 16. Modules & mixins moduleDebug def info "#{self.class}[#{object_id}]: #{to_s}" end end class Object include Debug end >> 2.info => "Fixnum[5]: 2" >> "foo".info => "String[70107061928320]: foo"
- 17. Collections & Enumerable class MyCollection include Enumerable def each ... end end >> MyCollection.instance_methods.sort => [:all?, :any?, :chunk, :collect, :collect_concat, :count, :cycle, :detect, :drop, :drop_while, :each, :each_cons, :each_entry, :each_slice, :each_with_index, :each_with_object, :entries, :find, :find_all, :find_index, :first, :flat_map, :grep, :group_by, :include?, :inject, :map, :max, :max_by, :member?, :min, :min_by, :minmax, :minmax_by, :none?, :one?, :partition, :reduce, :reject, :reverse_each, :select, :slice_before, :sort, :sort_by, :take, :take_while, :to_a, :zip]
- 18. method_missing magic class MyStruct def initialize values @values = values end def method_missing name, *args @values[name] end end >> struct = MyStruct.new foo: 123, bar: 456 => #<MyStruct:0x007fc2c21433b8 @values={:foo=>123, :bar=>456}> >> struct.foo => 123 >> struct.bar => 456
- 19. Dynamic definition class MyStruct def initialize values @values = values end def method_missing name, *args puts "Defining method #{name}" self.class.class_eval do define_method(name) { @values[name] } end send(name, *args) end end >> struct.foo Defining method foo => 123 >> struct.foo => 123
- 20. Pros Power and flexibility Developerproductivity and fun Raw execution speed Limited concurrency support Type-aware tool support Cons
- 21.
- 22. Io is arule 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.
- 23. Message passing Io> "oIolleH" reverse ==> Hello Io Io> list("iH", "oI") map(reverse) ==> list(Hi, Io) Io> list(1, 2, 3) map(** 2) sum ==> 14
- 24. Objects & Slots Io>Person := Object clone ==> Person_0x7f922c06ad00: type = "Person" Io> Person firstName := "John" ==> John Io> Person lastName := "Doe" ==> Doe Io> Person firstName ==> John
- 25. Defining methods Io> Personname := method ( firstName .. " " .. lastName ) Io> Person name ==> John Doe
- 26. Prototypal inheritance Io> Arthur:= Person clone ==> Arthur_0x7fd5406cd860: type = "Arthur" Io> Arthur name ==> John Doe Io> Arthur firstName = "Arthur" Io> Arthur lastName = "Dent" Io> Arthur name ==> Arthur Dent Io> Arthur proto ==> Person_0x7fd540693ed0: firstName = "John" lastName = "Doe" name = method(...) type = "Person"
- 27. Control structures Io> for(i,1, 3, i println) 1 2 3 ==> 3 Io> if(true, "Yes" println, "No" println) Yes ==> Yes
- 28. 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)
- 29. 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!
- 30. 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
- 31. Futures Io> page :=URL with( "http://google.co.uk/") @fetch Io> "I'm in the foreground" println I'm in the foreground Io> page size println 16906
- 32. Pros Tiny – idealfor embedded systems Prototypes and duck typing are very flexible Concurrency support Simple, consistent syntax Raw execution speed Small user community Cons
- 33.
- 34. Sometimes spectacularly smart,other times just as frustrating. You’ll get astounding answers only if you know how to ask the question.
- 35. 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.
- 36. 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.
- 37. 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.
- 38. 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].
- 39. Calculation with lists sum(0,[]). sum(Total, [Head|Tail]) :- sum(Sum, Tail), Total is Head + Sum. ?- sum(What, [1, 2, 3]). What = 6.
- 40. 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].
- 41. Solving (4×4) sudoku 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]). valid([]). valid([Head|Tail]) :- all_different(Head), valid(Tail).
- 42. Pros Solving logical andscheduling problems Natural language processing Artificial intelligence Scaling requires deep understanding Not a general-purpose language Simple procedural tasks are difficult Cons
- 43.
- 44. He was oftenawkward, was sometimes amazing, but always had a unique expression. Sometimes, his scissors let him do incredible things. Other times, he was awkward and humiliated.
- 45. 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
- 46. var & val scala>var a = 42 a: Int = 42 scala> a = a + 1 a: Int = 43 scala> val earth = "Harmless" earth: java.lang.String = Harmless scala> earth = "Mostly Harmless" <console>:8: error: reassignment to val earth = "Mostly Harmless" ^
- 47. Ranges & 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
- 48. Lists, sets &maps scala> val list = List(1, 2, 3) list: List[Int] = List(1, 2, 3) scala> list(1) res0: Int = 2 scala> "zero"::list res1: List[Any] = List(zero, 1, 2, 3) scala> Set(1, 2, 3) ++ Set(2, 3, 4) res2: 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) res3: java.lang.String = One
- 49. 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("DevCon") Hello DevCon, I'm Kerry.
- 50. Companion objects class Person(firstName:String, lastName: String) { ... } object Person { def find(id: Int) { val (first, last) = DB.people.find(id) new Person(first, last } }
- 51. Extending & traits classPerson(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.
- 52. List processing scala> valjedi = 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
- 53. Class hierarchy Any AnyVal AnyRef Float Int … ScalaObject … List Map Nothing Null
- 54. First-class XML scala> valpets = <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>)
- 55. 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'.
- 56. Concurrency with actors caseobject 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
- 57. Pros A modern versionof Java Mixins, pattern matching, blocks, XML Concurrency with actors & immutability Static typing Compromises with mutable state Cons
- 58.
- 59. Agent Smith wasan 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.
- 60. 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?"
- 61. Variables don’t change 1>Foo = 42. 42 2> Foo = Foo + 1. ** exception error: no match of right hand side value 43 3> Values = [1, 2, 3]. [1,2,3] 4> lists:append(Values, [4]). [1,2,3,4] 5> Values. [1,2,3]
- 62. 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]}
- 63. 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}
- 64. Basic functions -module(demo). -export([echo/1]). echo(Value) ->Value. 1> c(demo). {ok,demo} 5> demo:echo("Hello"). "Hello" 6> demo:echo(42). 42
- 65. 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).
- 66.
- 67.
- 68.
- 69. 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
- 70. 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}]
- 71. 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
- 72. 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
- 73. Monitor & 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.
- 74. 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.
- 76. His communication styleis 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.
- 77. 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
- 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. Data or code? 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
- 80. Vectors, sets &maps user=> (def numbers [1 2 3]) (1 2 3) user=> (conj numbers "forty-two") [1 2 3 "forty-two"] user=> (def crew #{:zaphod :trillian :marvin}) #'user/crew user=> (clojure.set/union crew #{:ford :zaphod :arthur}) #{:arthur :trillian :ford :zaphod :marvin} user=> (def home {:arthur :earth, :ford :betelgeuse, :marvin :sirius}) #'user/home user=> (home :arthur) :earth user=> (:arthur home) :earth
- 81. Defining functions user=> (defnanswer [] 42) #'user/answer user=> (answer) 42 user=> (defn treble [a] (* 3 a)) #'user/treble user=> (treble 20) 60
- 82. Destructuring params user=> (defboard [[:x :o :x] [:o :x :o] [:o :x :o]]) #'user/board user=> (defn centre [[_ [_ c _] _]] c) #'user/centre user=> (centre board) :x
- 83. Anonymous functions user=> (defntreble [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)
- 84. 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)))))
- 85. 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)
- 86. Lazy evaluation user=> (take5 (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
- 87. 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
- 88. Macro expansion user=> (defnunless [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
- 89. Transactional memory user=> (defford (ref {:name "Ford Prefect", :from "Guildford"})) #'user/ford user=> (deref ford) {:name "Ford Prefect", :from "Guildford"} user=> @ford {:name "Ford Prefect", :from "Guildford"} user=> (alter ford assoc :from "Betelgeuse") java.lang.IllegalStateException: No transaction running (NO_SOURCE_FILE:0) user=> (dosync (alter ford assoc :from "Betelgeuse")) {:name "Ford Prefect", :from "Betelgeuse"} user=> @ford {:name "Ford Prefect", :from "Betelgeuse"}
- 90. 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]
- 91. Agents in thebackground 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
- 92. Back to thefutures user=> (def ultimate-answer (future (do (Thread/sleep 2.4e17) 42))) #'user/ultimate-answer user=> @ultimate-answer 42
- 93. Pros A good lispimplementation 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
- 94.
- 95. Haskell represents purityand 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.
- 96. Type inference Prelude> :set+t Prelude> 42 42 it :: Integer Prelude> "Mostly harmless" "Mostly harmless" it :: [Char] Prelude> "black" == "white" False it :: Bool Prelude> 1/2 0.5 it :: Double
- 97. Defining functions Prelude> letdouble x = x * 2 double :: Num a => a -> a Prelude> double 4 8 Prelude> double 2.5 5.0 Prelude> let times x y = x * y times :: Num a => a -> a -> a Prelude> times 5 6 30
- 98. 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 *Main> double 2.5 <interactive>:1:8: No instance for (Fractional Integer) arising from the literal `2.5'
- 99. 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
- 100. Tuples & lists Prelude>let zaphod = ("Zaphod", "Beeblebrox", "Betelgeuse", 2) Prelude> let (_, _, _, numberOfHeads) = zaphod Prelude> let numbers = [1, 2, 3, 4] Prelude> let (head:tail) = numbers 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' Possible fix: add an instance declaration for (Num [Char]) In the expression: 1 In the expression: [1, "two"] In an equation for `it': it = [1, "two"]
- 101. Ranges & 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]
- 102. List comprehensions Prelude> letnumbers = [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)]
- 103. 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
- 104. 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
- 105. Type classes class Eqa 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
- 106. User-defined types module Mainwhere data Shape = Circle Float | Rectangle Float Float deriving show area :: Shape -> Float area (Circle r) = pi * r ^ 2 area (Rectangle x y) = x * y *Main> let circle = Circle 10 *Main> let rect = Rectangle 6 7 *Main> area circle 314.15927 *Main> area rect 42.0 *Main> [circle, rect] [Circle 10.0,Rectangle 6.0 7.0]
- 107. Record syntax module Mainwhere data Shape = Circle {radius :: Float} | Rectangle {width :: Float, height :: Float} deriving Show area :: Shape -> Float area (Circle r) = pi * r ^ 2 area (Rectangle x y) = x * y *Main> let circle = Circle 10 *Main> let rect = Rectangle 6 7 *Main> [circle, rect] [Circle {radius = 10.0},Rectangle {width = 6.0, height = 7.0}]
- 108. Monads A monad isa 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) )
- 109. Monads A monad isa 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) )
- 110. The maybe monad dataMaybe 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
- 111. Pros Pure functional languagewith 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
- 112. What I learnedfrom Seven Languages in Seven Weeks
- 113. 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
- 114. JVM or standalone? •Access to Java libraries • Deployment environments • Escape route for Java developers • Limitations (eg tail recursion)
- 115. Know what’s outthere • Languages • Features • First-class functions • List comprehensions • Pattern matching • Lazy evaluation
- 116. Dealing with concurrency • Immutability • Coroutines • Actors • Futures • Software Transactional Memory
- 117.