Understanding Haskell Documentation

In this post I will be giving an insight in reading haskell documentation

Product Example

1
2

product :: Num a => [a] -> a
-- The product function computes the product of a finite list of numbers.

Above is an extract from the Haskell documentation.

Line 1 shows the Type Signature of the product function, this shows the types of the inputs and the outputs in a convenient way.

All functions in Haskell return a single object, this could be a single number, tuple, list etc. The first part of this statement Num a is called a Type Class this is a more advanced topic and something we will discuss later.

The final part of the statement [a] -> a this is showing a list of something is given to the product function and a single something is returned. The type of the something must be a Num as it is stated in the Type Class.

Appending Two Lists

1
2

(++) :: [a] -> [a] -> [a]
-- Append two lists

Above is an extract from the Haskell documentation.

Again line 1 shows the Type Signature of the append operator. We know haskell returns only a single object so we know what the final [a] represents that means that the first two [a] must be the inputs to the function. So this function takes two lists of the same type (both are parameterised with a) and returns a new list of the same type of the input.