Haskell

Haskell

1. Commands

   • :set +t
     • Report types
   • ghci
     • Run compiler in interactive mode
   • let
     • Definition in local scope
   • :load :r
     • load and reload
   • show
     • Turns showable values into strings

2. Lazy

   • Does least work to get answer

3. Polymorphism

   • a
     • Allow any type of input
     • Items in list must be same type

4. Type classes

   • Integral
     • Int or integer
   • Fractional
     • Floating point or double
   • Ord
     • Any type compared with <

5. Functions

   • Higher Order Function
     • Function that takes another function as input
   • Recursive Functions
     • Functions defined in terms of themselves
   • Identity function
     • Works on finite lists
     • Returns same value, e.g. reverse . reverse

6. Syntax

   • Curried Notation
     • curried: a -> b -> c uncurried: (a, b) -> c
     • Turns multiple arguments into 1 -returns function
     • All functions in Haskell are curried
     • Allows partial application
       • Passing less than the full number of arguments
         • Doesn't have to be defined over empty lists
   • Lambda Abstractions
     • Function without a name
     • Allows creation of functions on the fly
     • Good for simple calculations like 2^x
       • map (\x -> 2^x) [1..20]
   • Function definitions
     • Pattern Matching
       • safeTail [ ] = [ ] safeTail (_:xs) = xs
     • Conditional
       • safeTail xs = if null xs then [ ] else drop 1 xs
     • Guarded
       • safeTail xs | null xs = [ ] | otherwise = drop 1 xs