Notes from 11/9

Announcements

Final exam was scheduled for December 21st. That’s very late. Instead, we’ll either:

  1. Do it for ~1 hour in class on December 14, or
  2. Do a take-home exam where you receive it on 14th, due a few days later.

Will confirm next week.

Modules

  • Imports, qualified, renames.
  • Selective exports
  • Abstract data types by not exporting constructor.
  • newtype
  • Example: case-insensitive strings

A technique for abstract data types, sometimes called a “smart constructor”. Define a data type, and make the type itself public, but the constructor(s) are private.

Maps and Sets

  • qualified import
  • where to find docs
  • fold

Lists are convenient, but not very efficient.

import qualified Data.Map as M
tally :: Char -> M.Map Char Int -> M.Map Char Int
tally c m =
  case M.lookup c m of
    Nothing -> M.insert c 1 m
    Just k -> M.insert c (k+1) m

Input/Output

  • IO monad
  • putStr[Ln], getLine, print
  • System.IO
  • withFile, hPutStr, hGetLine, …
main = return ()
mymain = do
  putStrLn "Hello, world."
  putStr "What is your name? "
  name <- getLine
  putStrLn $ "Welcome, " ++ name
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