Haskell¶

Understand Functions Are Functors

Functions are functors is a basic idea in funcitonal programming. However, the (->) r formats of functions are confusing and misleading, What's worse, affected by imperative language features, there was an misunderstanding about how the original structure is hold by a functor. To be more concrete, this blog talks about the question: why result of fmap (*2) (+100) 1 is 202, not 102?

Why Applicative Functor Currying While Fmap

Why applicative functor could currying a function while calling fmap? What are processes to calculate it?

ghci> (\x y z -> [x, y, z]) <$> (+3) <*> (*2) <*> (/2) $ 5
[8.0,10.0,2.5]

This is my anwser for the question Applicative functors: why can fmap take a function with more than one argument? in stackoverflow.

What is the purpose of the reader monad?

This blog answered the question of What is the purpose of the reader monad? in my view. The original answer stays on stackoverflow.