Haskell Day5

About Functions

Today I learned about function composition thing in Haskell. Firstly I start with simple composition example. In math we can very easily compose two or more functions .İ.e : there are two functions f(x) and g(x) and the composition function can be writed like t(x) = g o f or h(x) = f o g t(x) and h(x) will different functions. In Haskell we can combine function with using a functions as a parameter like:

f x = x + 2

g x = x * 3

a = f (g 4)

b =g(f 4)

main = do

           print(a)

           print(b)

Program will return 14 and 18 .We must use parentheses otherwise we can use “.”

f ( g x ) = = (f . g) x

Lets start with fundamental thing of structural programming : “decision part”.In Haskell we use If,Then and Else structure for making decision. For example there are three possibility about f(x).

f(x) can be positive or negative or zero so

mysig x =

             if x < 0 – deciding

                    then -1 – if firs condition ok what happened

                    else if x >0 – second condition

                          then 1 – if second condition ok what happened

                          else 0 – what happened if all of condition is wrong

main=print(mysig (0))

it will return 0.Also this function can be write like this

mysig x

         | x < 0 = -1

         | x > 0 = 1

         | otherwise = 0

It is so similar to functions in math.