Writing INI parser

In this recipe, we will further build on the concepts of Functor, Applicative, and monad, and build a parser for the INI file from scratch. We will write a simple parser, and define its Functor, Applicative, and monad instances. Then, we will slowly build upon the concept to finally build an INI parser. 

The INI file is usually used as a configuration file. A typical INI file contains the number of sections, each section representing a set of name-value assignments. A sample INI file may look like this: 

    [Section]
    name1 = value1
    name2 = value2

    [Section2]
    name1 = value1
    name3 = value3

How to do it...

1. Create a new project ini-parser using the simple Stack template:

        stack new ini-parser simple

2. Open the file src/Main.hs for editing.
3. After the initial module header, add the following imports:

        import Data.Functor
        import Control.Applicative
        import Control.Monad
        import Data.Map hiding (empty)
        import Data.Char

4. Define...