davidallsopp

import functools

def compose(*functions):
    "Compose multiple functions together. See https://mathieularose.com/function-composition-in-python/"
    return functools.reduce(lambda f, g: lambda x: f(g(x)), functions)

# More limited case of just two functions:
#def compose2(f, g):
#    return lambda x: f(g(x))

davidallsopp

-- Let's say that we want to print out each of a list of items:

λ>map print [1,2,3]

<interactive>:13:1:
    No instance for (Show (IO ())) arising from a use of ‘print’
    In a stmt of an interactive GHCi command: print it


-- That doesn't work!...

davidallsopp

λ> let fib = 0: 1: zipWith (+) fib (tail fib)

λ> take 10 fib
[0,1,1,2,3,5,8,13,21,34]

λ> fib !! 100
354224848179261915075

λ> fib !! 1000
434665576869374564356885276750406258025646605173717804024817290895365554179490518904038798400792551692959225930803226347

davidallsopp

λ> import Data.Functor.Compose

-- List of lists
λ> getCompose $ fmap (+1) $ Compose [[],[1],[2,3],[4,5,6]]

[[],[2],[3,4],[5,6,7]]

-- List of Maybe
λ> getCompose $ fmap (+1) $ Compose [Just 1, Just 2, Nothing, Just 3]

davidallsopp

module ReaderMonad where

import Control.Monad.Reader

stuff :: Reader Int String
stuff = do
  s <- ask
  return (show s ++ " green bottles")
    
main :: IO ()

davidallsopp

module WriterMonad where

-- From http://learnyouahaskell.com/for-a-few-monads-more
-- This example no longer works without tweaking - see
-- http://stackoverflow.com/questions/11684321/how-to-play-with-control-monad-writer-in-haskell
-- just replace the data constructor "Writer" with the function "writer" in the line marked "here"
-- That changed with mtl going from major version 1.* to 2.*, shortly after LYAH and RWH were written

import Control.Monad.Writer
      

davidallsopp

module TrivialMonad where

-- See also http://hackage.haskell.org/package/transformers-0.4.1.0/docs/src/Data-Functor-Identity.html#Identity

import Control.Applicative (Applicative(..)) -- import type and all exported constructors using '(..)'
-- How is that different from "import Control.Applicative"
import Control.Monad       (liftM, ap)

data Trivial a = Trivial a deriving (Show) -- wrapper type

davidallsopp

module FindFiles where

import System.FilePath.Find

-- Can't install FileManip on Windows because it depends on "unix", which (surprise!) can't be installed 
-- on Windows without Cygwin etc. Instead, install filemanip not FileManip (obviously ?!)
-- which depends on unix-compat, which is fine on Windows

main :: IO () 
main = do

davidallsopp

module ZipExample where

-- https://hackage.haskell.org/package/zip-archive
-- https://hackage.haskell.org/package/zip-archive-0.2.3.5/docs/Codec-Archive-Zip.html
-- Example usage: https://github.com/jgm/zip-archive/blob/master/Zip.hs

import Codec.Archive.Zip
import qualified Data.ByteString.Lazy as B
import Control.Applicative ( (<$>) )

davidallsopp

module ZipConduit1 where

-- requires zip-conduit package
-- slightly adapted from the docs at:
-- https://hackage.haskell.org/package/zip-conduit-0.2.2.1/docs/Codec-Archive-Zip.html

import Codec.Archive.Zip

main :: IO ()
main = do