Chapter 4. Using GHC
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## Chapter 4. Using GHC

## 4.1. Getting started: compiling programs

In this chapter you'll find a complete reference to the GHC command-line syntax, including all 400+ flags. It's a large and complex system, and there are lots of details, so it can be quite hard to figure out how to get started. With that in mind, this introductory section provides a quick introduction to the basic usage of GHC for compiling a Haskell program, before the following sections dive into the full syntax.

Let's create a Hello World program, and compile and run it. First, create a file `hello.hs` containing the Haskell code:

    main = putStrLn "Hello, World!"

To compile the program, use GHC like this:

    $ ghc hello.hs

(where `$` represents the prompt: don't type it). GHC will compile the source file `hello.hs`, producing an object file `hello.o` and an interface file `hello.hi`, and then it will link the object file to the libraries that come with GHC to produce an executable called `hello` on Unix/Linux/Mac, or `hello.exe` on Windows.

By default GHC will be very quiet about what it is doing, only printing error messages. If you want to see in more detail what's going on behind the scenes, add `-v` to the command line.

Then we can run the program like this:

    $ ./hello
    Hello World!

If your program contains multiple modules, then you only need to tell GHC the name of the source file containing the `Main` module, and GHC will examine the `import` declarations to find the other modules that make up the program and find their source files. This means that, with the exception of the `Main` module, every source file should be named after the module name that it contains (with dots replaced by directory separators). For example, the module `Data.Person` would be in the file `Data/Person.hs` on Unix/Linux/Mac, or `Data\Person.hs` on Windows.

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Chapter 3. Using runghc | Home | 4.2. Options overview