haskell.md

gist-id: cd76ef36afbe36e7a65f

Cabal

• cabal - the simple guide
• Cabal-sandbox

tutorials

• یه برگه تقلب خوب برای هسکل
• [http://www.seas.upenn.edu/~cis194/spring13/](Introduction to Haskell-Spring 2013)
• bitemyapp/learnhaskell
• A Haskell CheatSheet in PDF and literate source formats.
• Introduction to Haskell/ University of Virginia CS 1501 Lectures Spring 2013

هسکل چیست؟

Haskell is a purely functional, lazy, statically typed programming language.

Purely functional

• Functions are values
• Values never change

Lazy

Statically Typed

چرا باید آن را یاد بگیریم

• سخت نیست بلکه متفاوت است.
• سی - مهندسین
• جاوا- کسب-و-کاربر
• هسکل- ریاضیات

Simple Conditionals

posOrNeg x =
	if x >= 0
	then "Positive"
	else "Negative"

Pure Functions

All Haskell functions are pure

• Cannot modify state
• Cannot depend on state
• Given the same arguments, always returns the same output

• print to console > Note pure
• Read file -> Not pure
• Compute the length of a list -> pure
• get the current time -> Not pure
• get a random number -> Not pure

Recursion

pow2 n = 
	if n == 0
	then 1
	else 2 * ( pow2 (n-1) )

repeatString str n =
	if n == 0
	then ""
	else str ++ ( repeatString str (n-1))

List

x = [1,2,3]
empty = []
y = 0 : x
x' = 1 : (2 : (3 : [] ) )
x'' = 1 : 2 : 3 : []

concat

`` [1, 2, 3] ++ [4, 5] "hello " ++ "world"

## homogenous lists

error = [1, "hello", 2]

* head
* tail
* null


# Strings

str = "abcde" str` = 'a' : 'b' : 'c' : 'd' : 'e' : []

# تاریخچه