let.hs

-- local scope

-- cylinder surface
cylinder :: (RealFloat a) => a -> a -> a
cylinder r h =
    let sideArea = 2 * pi * r * h
        topArea = pi * r ^ 2
    in  sideArea + 2 * topArea

-- let are expressions themselves
-- where are syntactic constructs

-- let to introduce functions

-- [let square x = x * x in (square 5, square 3, square 2)]

-- let inline
-- (let a = 100; b = 200; c = 300 in a*b*c, let foo="Hey "; bar = "there!" in foo ++ bar) 

--- (let (a,b,c) = (1,2,3) in a+b+c) * 100  

calcBmis :: (RealFloat a) => [(a, a)] -> [a]  
calcBmis xs = [bmi w h | (w, h) <- xs]  
    where bmi weight height = weight / height ^ 2 

calcBmis' :: (RealFloat a) => [(a, a)] -> [a]  
calcBmis' xs = [bmi | (w, h) <- xs, let bmi = w / h ^ 2]  

calcBmisF :: (RealFloat a) => [(a, a)] -> [a]  
calcBmisF xs = [bmi | (w, h) <- xs, let bmi = w / h ^ 2, bmi >= 25.0]