Haskell

1
???? Haskell

• ?????

Eugeny L Yakimovitch http//desk.by/ewger
2008
2
??????????

• Thompson S. Haskell The Craft of Functional
  Programming. 2-nd edition, Addison-Wesley, 1999.
• Bird R. Introduction to Functional Programming
  using Haskell. 2-nd edition, Prentice Hall Press,
  1998.
• ?????? ?. ?. ?????????????? ???????????????? ??
  ????? Haskell. ?.??? ?????, 2007
• Koen Lindstruem Claessen // http//www.cs.chalmers
  .se/Cs/Grundutb/Kurser/funht/index.html,
  2008-02-04
• ??????

3
??????????

• ????? ?????? ?????????? ??? ????????
  ???????????????? ??????????
• HUGS
• GHC

4
???????????

• ?????? ?????????????? ????? ?????????????? ??
• ????????? ??????? ??????????
• ??????? (?????, ???????????) ????? ??????,
  ?????????? ?? ?????????? ??????????????
  ??????????
• ?????? ?????????? (?????????????) ?????????
  ???? ??????????? ??????? fS-gtT, ??? S,T
  ????????? ????
• ???????? ???? ???????????? ????????? ? ??????
  ???????? ????? ???
• ??????? ?????? ???????? ??????? ??? ?????
  ????????, ??????? ????????? ? ???? ?????????? ?
  ??????????? ?????? ???????
• ?????? ????????? ??????????? ??? (??. haskell.org)

5
??????????? ??
dynamically typed
pure functions
higher-order functions
statically typed
type inference
real-time
immutable datastructures
polymorphism
overloading
concurrency
high performance
distribution
parameterized types
lazy
virtual machine
Java
reflection
type classes
object oriented
compiler
interpreter
meta-programming
Haskell
unification
C
backtracking
6
??????? ??????

• ????????? ?????????? ?????????
• ?????????? ???. ???????? ???????
• ??????????? ???????????? ????????
• ?????????????? ?????????? ???????????? ?????
  ?????????
• ?????????????? ???????? ?????????
• ????????????? ????????????? ????????

7
???????? ? ?????????

• ???????? ????????????? ????? ???????? ????????
• ????????? ?????????? ? ?????????? ??????????
  (??????????) ??????? ? ????????? (??. ??????
  ??????????). ?????????? (????????) ????????????
  ?? ????????? ????????.

• Preludegt 'c'
• 'c' Char
• Preludegt 3
• 3 Integer
• Preludegt not True
• False Bool

• Preludegt 5gt7
• False Bool
• Preludegt 12
• 3 Integer

8
???????? ?????????

• ???????? ????????? ???????? ??????????
  ??????????, ? ?? ???????? ?????? ????????????
  ???????? ??????????? (?.?. ??? ?? ??????????
  ????????? ? ?????????? ??????????)

Preludegt if 2gt3 then 4 else 5 5 Integer
Preludegt if if 1lt2 then 3lt2 else 4lt5 then 'a'
else 'b' ?
9
?????? ?????????

• ??? ?????? ?????? ????????? ? ???????? ???????
  ????????? ?????? ???????????? ????????? ????? \
• ? ???????? ????? ??????????????????
• -gt

gt (\x -gt \y -gt x y) 1 2 3
10
??????? ? ??????

• module IntroExample
• (someFunction)
• Where
• someFunction Int -gt Int -gt Int
• someFunction n
• someFunction n (xxs) (x n) someFunction n
  xs
• -- n - ?????, ??????? ?????????? ?????????
  ? ??????? ???????? ??????.

11
?????????? ?????

• module TypeInference
• (Zero, Succ, One, Two, Three, Four, zero, one,
  two, three, four, Add, Mul, Fac)
• where

???????? http//www.willamette.edu/fruehr/haskel
l/evolution.html
12

• --------------------------------------------------
  -----------------------------
• -- ?????????????? ???, ?????????????? ???????? 0.
• data Zero
• --------------------------------------------------
  -----------------------------
• -- ?????????????? ???, ?????????????? ?????????
  ???????? ?? ???????? ?????.
• data Succ n

13

• --------------------------------------------------
  ------------------------------
• -- ???????? ????? ??? ????????????? ????? ?? 1 ??
  4 (??? ???????). ???????????
• -- ????????????? ????? ?? ??????????? ?????.
• type One Succ Zero
• type Two Succ One
• type Three Succ Two
• type Four Succ Three
• --------------------------------------------------
  ------------------------------
• -- ??????? ??? ????????????? ????????????? ?????
  ?? 1 ?? 4 (??? ???????).
• zero undefined Zero
• one undefined One
• two undefined Two
• three undefined Three
• four undefined Four

14

• --------------------------------------------------
  ------------------------------
• -- ????? ??? ????????????? ???????? ???????? (?
  ????????? ?????? ?????).
• class Add a b c a b -gt c where
• add a -gt b -gt c
• --------------------------------------------------
  ------------------------------
• -- ?????????? ?????? Add ??? ?????????????
  ???????? ????????.
• instance Add Zero b b
• instance Add a b c gt Add (Succ a) b (Succ c)

15

• --------------------------------------------------
  ------------------------------
• -- ????? ??? ????????????? ???????? ????????? (?
  ????????? ?????? ?????).
• class Mul a b c a b -gt c where
• mul a -gt b -gt c
• --------------------------------------------------
  ------------------------------
• -- ?????????? ?????? Mul ??? ?????????????
  ???????? ?????????.
• instance Mul Zero b
  Zero
• instance (Mul a b c, Add b c d) gt Mul (Succ a) b
  d

16

• --------------------------------------------------
  ------------------------------
• -- ????? ??? ????????????? ???????? ??????????
  ?????????? (? ????????? ??????
• -- ?????).
• class Fac a b a -gt b where
• fac a -gt b
• --------------------------------------------------
  ------------------------------
• -- ?????????? ?????? Fac ??? ?????????????
  ???????? ?????????? ??????????.
• instance Fac Zero
  One
• instance (Fac n k, Mul (Succ n) k m) gt Fac (Succ
  n) m

17
????-?????

• Writes baz to the file called foo.
• No result displayedwonder why not?

Preludegt writeFile "foo" "baz" Preludegt
18
?????? ?????-??????

• module Main
• where
• import IO
• main do hSetBuffering stdin LineBuffering
• doLoop

19

• doLoop do putStrLn "Enter a command rFN wFN or
  q to quit"
• command lt- getLine
• case command of
• 'q'_ -gt return ()
• 'r'filename -gt do putStrLn
  ("Reading " filename)
• doRead filename
• doLoop
• 'w'filename -gt do putStrLn
  ("Writing " filename)
• doWrite filename
• doLoop
• _ -gt doLoop

20

• doRead filename bracket (openFile filename
  ReadMode)
• hClose
• (\h -gt do contents lt-
  hGetContents h
• putStrLn "The
  first 100 chars"
• putStrLn
  (take 100 contents))
• doWrite filename do putStrLn "Enter text to go
  into the file"
• contents lt- getLine
• bracket (openFile filename
  WriteMode) hClose
• (\h -gt hPutStrLn h
  contents)