Introduction To Haskell

Lecture 7

The Prolific Haskell Community

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Review of Homework 6

Detect whether a password is strong


-- Designed by Jamie M. Swogger

import Data.Char
import Data.List

strong x = length x > 14
    && any isLower x
    && any isUpper x
    && any isDigit x


-- Designed by Justin Dao
-- (Similar design by Zachary A. Brown)

import Data.Set

strong :: String -> Bool
strong y
    | length y < 15 = False
    | intersection (fromList ['A'..'Z']) (fromList y) == fromList [] = False
    | intersection (fromList ['a'..'z']) (fromList y) == fromList [] = False
    | intersection (fromList ['0'..'9']) (fromList y) == fromList [] = False
    | otherwise = True


-- Designed by Christopher D. Mata

import Data.Char

strong :: String -> Bool
strong [] = False
strong x = checkLower x 
    && checkUpper x 
    && checkNum x 
    && checkLength x

checkLower :: String -> Bool
checkLower [] = False
checkLower (x:xs)
    |(isLower x) = True
    |otherwise = checkLower xs

checkUpper :: String -> Bool
checkUpper [] = False
checkUpper (x:xs)
    |(isUpper x) = True
    |otherwise = checkUpper xs

checkNum :: String -> Bool
checkNum [] = False
checkNum (x:xs)
    |(isDigit x) = True
    |otherwise = checkNum xs

checkLength :: String -> Bool
checkLength [] = False
checkLength x
    |(length x > 14) = True
    |otherwise = False


-- Designed by Jared Candelaria

import Data.Char

strong :: String -> Bool
strong password = all ($ password) requirements
    where
        requirements = [minLength 15, 
                        any isUpper, 
                        any isLower, 
                        any isDigit]
        minLength n str = n <= length str

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Hackage

The ultimate collection of Haskell packages

Hackage + Cabal

You should use a tool called Cabal

Cabal is a command-line tool that installs packages and their dependencies

For example, try installing the HTTP library
```
cabal install HTTP
```

Cabal

Common Architecture for Building Applications and Libraries

fetches
configures
compiles
installs

Cabal Walkthrough

Let's install and use the HTTP package

Refresh the list of packages
Install the HTTP package
Use it!

1. Refresh the list

Download the most recent list of packages


cabal update

2. Install the package

Find any package from Hackage


cabal install HTTP

3. Use

Cabal takes care of installing the package.

The library can now be imported.


import Network.HTTP

Using Network.HTTP

All packages come with documentation on Hackage

Let's take a look at one of the functions in Network.HTTP

simpleHTTP takes in a Request object, and returns an IO Monad

Try it out


Prelude> import Network.HTTP

Prelude Network.HTTP> :t simpleHTTP
simpleHTTP
  :: HStream ty =>
     Request ty -> IO (Network.Stream.Result (Response ty))


Prelude Network.HTTP> let myRequest 
                      = getRequest "http://duckduckgo.com"

Prelude Network.HTTP> simpleHTTP myRequest >>= getResponseBody
"<!DOCTYPE html>..."

>>=


Prelude Network.HTTP> simpleHTTP myRequest >>= getResponseBody

Huh... What's that?


Prelude Network.HTTP> :t (>>=)
(>>=) :: Monad m => m a -> (a -> m b) -> m b

>>= is called the bind operator

MONADS!

Monad

Stay tuned till next time for a peek into Monads

Homework

Fill out this week's form!
Find the point of intersect of two lines using a package from Hackage
If you need help, address the Haskell community (Wiki, IRC, etc)