Haskell_ 003 Typeclass

A typeclass is a sort of interface that defines some behavior.

If a type is a part of a typeclass, that means that it supports and implements the behavior the typeclass describes.

Type signature of the == function

1. ghci> :t (==)  
2. (==) :: (Eq a) => a -> a -> Bool  

The equality operator, == is a function. +, *, -, / and pretty much are all operators. 

If a function is comprised only of special characters, it's considered an infix function by default. If we want to examine its type, pass it to another function or call it as a prefix function, we have to surround it in parentheses.

class constraint. : Everything before the => symbol

The equality function takes any two values that are of the same type and returns a Bool.  The type of those two values must be a member of the Eq class (this was the class constraint).

The Eq typeclass provides an interface for testing for equality

All standard Haskell types except for IO and functions are a part of the Eq typeclass.

Type signature of the elem  function

The elem function has a type of (Eq a) => a -> [a] -> Bool because it uses == over a list to check whether some value re looking for is in it

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