From Ruby to Haskell (Kansai Yami RubyKaigi)

From Ruby to Haskell
Kansai Yamiruby Kaigi
Nov 13, 2011
Tatsuhiro Ujihisa

Sunday, November 13, 2011

Agenda
• Haskell (introduction)
• Haskell (for beginners)
• Self-introduction
• Haskell (for average people)
• Haskell (for pro)


Haskell (1/3)


Haskell
• Programming language
• 1990~
• GHC


Haskell
• Strong static-typed
• Interpreter & native compiler
• Lazy evaluation

main = print "hello"


FizzBuzz in Ruby
1 (1..100).each do |i| 1 def main
2 puts ﬁzzbuzz
2 puts i % 15 == 0 ? 'FizzBuzz' :
3 end
3 i % 5 == 0 ? 'Buzz' :
4
4 i % 3 == 0 ? 'Fizz' : 5 def ﬁzzbuzz
5 i 6 (1..100).map {|i|
6 end 7 i % 15 == 0 ? 'FizzBuzz' :
8 i % 5 == 0 ? 'Buzz' :
9 i % 3 == 0 ? 'Fizz' :
10 i
11 }
12 end
13
14 main


FizzBuzz in Ruby
1 def main 1 def main
2 puts fizzbuzz 2 puts fizzbuzz
3 end 3 end
4 4
5 def fizzbuzz 5 def fizzbuzz
6 f = -> i do 6 (1..100).map {|i|
7 i % 15 == 0 ? 'FizzBuzz' : 7 i % 15 == 0 ? 'FizzBuzz' :
8 i % 5 == 0 ? 'Buzz' : 8 i % 5 == 0 ? 'Buzz' :
9 i % 3 == 0 ? 'Fizz' : 9 i % 3 == 0 ? 'Fizz' :
10 i 10 i
11 end 11 }
12 (1..100).map &f 12 end
13 end 13
14 14 main
15 main

FizzBuzz in Haskell
1 def main 1 main = print fizzbuzz
2 puts fizzbuzz 2
3 end 3 fizzbuzz = map f [1..100]
4 4 where f n
5 def fizzbuzz 5 | n `rem` 15 == 0 = "FizzBuzz"
6 f = -> i do 6 | n `rem` 5 == 0 = "Buzz"
7 i % 15 == 0 ? 'FizzBuzz' : 7 | n `rem` 3 == 0 = "Fizz"
8 i % 5 == 0 ? 'Buzz' : 8 | otherwise = show n
9 i % 3 == 0 ? 'Fizz' :
10 i
11 end
12 (1..100).map &f
13 end
14
15 main

Haskell (2/3)


1 main = print (a + b) 1 main = print (a + b)
2 a=1 2 a = 1 :: Int
3 b=2 3 b :: Int
4 b=2

1 main = print (a + b)
2 a = 1 :: Int
1 a.hs:4:5:
3 b :: Int 2 No instance for (Fractional Int)
4 b = 2.1 3 arising from the literal `2.1'
4 Possible ﬁx: add an instance declaration for (Fractional Int)
5 In the expression: 2.1
6 In an equation for `b': b = 2.1
7


Type and type-class
• type (in Haskell) =~ class (in Ruby)
• type class (in Haskell) =~
module (in Ruby)

• Int type =~ Fixnum class
• Num type-class =~ Numeric module


Literals
• Ruby: only one type
• 1 (always Fixnum)
• "hello" (always String)
• Haskell: compiler infers
• 1 (Int? Integer? Float? Rational?)
• "a" (String? Test? ByteString?)

error 2 a = 1 :: Int
3 b = 2.1

ok 2 a=1
3 b = 2.1

b and (a+b) can be Float, Double or Rational


Lists
• [1, 2, 3]
• 1 : 2 : 3 : []
• ["a", "b", "c"]
• [1, 2, "a"] ERROR


Functions
• call
• fa
• gab
• deﬁne
• f a = something
• g a b = something

Operators
• call
• 1+2
• (+) 1 2
• 1 `g` 2
• deﬁne
• a + b = something

Interesting operators
•$
• f (g (h a b)))
• f$g$hab
• a : b : c : [] == [a, b, c]
• expected @=# actual


Combining actions
main = print [1, 2, 3] >> print "hi"

1 main = do
2 print [1, 2, 3]
3 print "hi"

main = do { print [1, 2, 3]; print "hi" }


only for side eﬀect
• Ruby
• puts 'hi'
puts 'yo'
• Haskell • puts 'hi'; puts 'yo'
• do
putStrLn "hi"
putStrLn "yo"
• putStrLn "hi" >> putStrLn "yo"

side eﬀect to get a val
• Ruby •Haskell
• a = gets • do
pa a <- getContent
print a
• getContent >>= print


self-introduction


Tatsuhiro Ujihisa
• @ujm
• Vancouver
• HootSuite media inc
• Vim


• http://ujihisa.blogspot.com
• http://vim-users.jp
• http://github.com/ujihisa


Haskell (3/3)


re: FizzBuzz in Haskell
1 def main 1 main = print fizzbuzz
2 puts fizzbuzz 2
3 end 3 fizzbuzz = map f [1..100]
4 4 where f n
5 def fizzbuzz 5 | n `rem` 15 == 0 = "FizzBuzz"
6 f = -> i do 6 | n `rem` 5 == 0 = "Buzz"
7 i % 15 == 0 ? 'FizzBuzz' : 7 | n `rem` 3 == 0 = "Fizz"
8 i % 5 == 0 ? 'Buzz' : 8 | otherwise = show n
9 i % 3 == 0 ? 'Fizz' :
10 i
11 end
12 (1..100).map &f
13 end
14
15 main

output
1 main = print ﬁzzbuzz ["1","2","Fizz","4","Buzz","Fiz
2 z","7","8","Fizz","Buzz","11","
3 ﬁzzbuzz = map f [1..100] Fizz","13","14","FizzBuzz","16
4 where f n ","17","Fizz","19","Buzz","Fizz
","22","23","Fizz","Buzz","26",
5 | n `rem` 15 == 0 = "FizzBuzz"
"Fizz","28","29","FizzBuzz","3
6 | n `rem` 5 == 0 = "Buzz"
1","32","Fizz","34","Buzz","Fiz
7 | n `rem` 3 == 0 = "Fizz" z","37","38","Fizz","Buzz","41
8 | otherwise = show n ","Fizz","43","44","FizzBuzz","
46","47","Fizz","49","Buzz","F
izz","52","53","Fizz","Buzz","5
6","Fizz","58","59","FizzBuzz"
,"61","62","Fizz","64","Buzz","
like p Fizz","67","68","Fizz","Buzz","
71","Fizz","73","74","FizzBuzz
","76","77","Fizz","79","Buzz",
"Fizz","82","83","Fizz","Buzz",

output
1
1 main = mapM_ putStrLn ﬁzzbuzz 2
2 Fizz
4
3 ﬁzzbuzz = map f [1..100] Buzz
4 where f n Fizz
7
5 | n `rem` 15 == 0 = "FizzBuzz" 8
6 | n `rem` 5 == 0 = "Buzz" Fizz
Buzz
7 | n `rem` 3 == 0 = "Fizz" 11
Fizz
8 | otherwise = show n 13
14
FizzBuzz
16
17
Fizz
19
like puts Buzz
Fizz
22
23
Fizz

mapM_
• f x >> f y >> f z
• do
fx
fy
fz
• mapM_ f [x, y, z]


mapM_
• ((f x) >> f y) >> f z
• foldl1 (>>) $ map f [x, y, z]
• f x >> (f y >> (f z))
• foldr1 (>>) $ map f [x, y, z]
• sequence_ (map f [x, y, z])

1 main = mapM_ putStrLn fizzbuzz 1 main = mapM_ putStrLn fizzbuzz
2 2
3 fizzbuzz = map f [1..100] 3 fizzbuzz = map f [1..100]
4 where f n 4 where f n = case () of
5 | n `rem` 15 == 0 = "FizzBuzz" 5 n `rem` 15 == 0 -> "FizzBuzz"
6 | n `rem` 5 == 0 = "Buzz" 6 n `rem` 5 == 0 -> "Buzz"
7 | n `rem` 3 == 0 = "Fizz" 7 n `rem` 3 == 0 -> "Fizz"
8 | otherwise = show n 8 otherwise -> show n


map, flip, and for
• map f list
• flip map list f
• mapM_ f list
• flip mapM_ list f
• forM_ list f

1 main = mapM_ putStrLn ﬁzzbuzz
2
3 ﬁzzbuzz = map f [1..100]
4 where f n = case () of _
5 | n `rem` 15 == 0 -> "FizzBuzz"
6 | n `rem` 5 == 0 -> "Buzz"
7 | n `rem` 3 == 0 -> "Fizz"
1 import Control.Monad (forM_)
8 | otherwise -> show n
2 main = forM_ [1..100] f
3 where
4 f n = putStrLn $ case () of _
5 | n `rem` 15 == 0 -> "FizzBuzz"
6 | n `rem` 5 == 0 -> "Buzz"
7 | n `rem` 3 == 0 -> "Fizz"


1 import Control.Monad (forM_)
2 main = forM_ [1..100] $ n ->
3 putStrLn $ case () of _
4 | n `rem` 15 == 0 -> "FizzBuzz"
5 | n `rem` 5 == 0 -> "Buzz"
6 | n `rem` 3 == 0 -> "Fizz"
1 import Control.Monad (forM_)7 | otherwise -> show n
2 main = forM_ [1..100] f
3 where
4 f n = putStrLn $ case () of _
5 | n `rem` 15 == 0 -> "FizzBuzz"
6 | n `rem` 5 == 0 -> "Buzz"
7 | n `rem` 3 == 0 -> "Fizz"


Haskell as shell scripts
• Succinct expressions
• Powerful list-manipulation
• Powerful text-manipulation
• Reasonably fast to boot
• Healthy


Parsec
• Parser combinators
• Standard library
• No need for handling state
explicitly


Haskell web framework
• Yesod
• Snap (framework)
•


Appendix
• IDE-integration
• run on the IDE
• keyword completion
• Prelude type/function completion
• module name completion
• third party t/f completion
• pragma completion

quickrun.vim
• DEMO
• runghc
• ghc


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