lesson2.hs

import System.IO
import Data.List

lucky :: (Integral a) => a -> String  
lucky 7 = "LUCKY NUMBER SEVEN!"  
lucky x = "Sorry, you're out of luck, pal!"   

{-when you call 'lucky', patterns will be checked from top to bottom and when it conforms with the pattern the function will be used-}

sayMe :: (Integral a) => a -> String  
sayMe 1 = "One!"  
sayMe 2 = "Two!"  
sayMe 3 = "Three!"  
sayMe 4 = "Four!"  
sayMe 5 = "Five!"  
sayMe x = "Not between 1 and 5"  

{- below is a recursive function-}
factorial :: (Integral a) => a -> a  
factorial 0 = 1  
factorial n = n * factorial (n - 1) 

{-below is a function that uses pattern matching on tuples-}
addVectors :: (Num a) => (a, a) -> (a, a) -> (a, a)  
addVectors (x1, y1) (x2, y2) = (x1 + x2, y1 + y2)   

first :: (a, b, c) -> a  
first (x, _, _) = x  
  
second :: (a, b, c) -> b  
second (_, y, _) = y  
  
third :: (a, b, c) -> c  
third (_, _, z) = z   {-remember, _ means that we don't care what part that is-}

head' :: [a] -> a  
head' [] = error "Can't call head on an empty list, dummy!"  
head' (x:_) = x  
{-guards are indicated by their pipes | such as this that are added to their parameters
bmiTell :: (RealFloat a) => a -> a -> String  
bmiTell weight height  
    | weight / height ^ 2 <= 18.5 = "You're underweight, you emo, you!"  
    | weight / height ^ 2 <= 25.0 = "You're supposedly normal. Pffft, I bet you're ugly!"  
    | weight / height ^ 2 <= 30.0 = "You're fat! Lose some weight, fatty!"  
    | otherwise                 = "You're a whale, congratulations!"  -}