The Haskell Platform
The fastest and easiest way to install Haskell is through the Haskell Platform. It includes the compiler (GHC), the build system (Cabal), the base libraries, and a few other helpful tools. It should only take a few seconds to install everything. When it finishes installing, open your console and type the commands shown below to check if it installed correctly.
Throughout this book, examples of input to your console will be shown
as lines starting with a
$ character. Type whatever follows on
the same line into your console. The lines that come afterward are the
ouput of the command.
$ ghc --version The Glorious Glasgow Haskell Compilation System, version 8.4.2 $ cabal --version cabal-install version 22.214.171.124 compiled using version 126.96.36.199 of the Cabal library
If your output looks like this, then you are ready to go!
Running the Interpreter
GHCi (which is an acronym for Glasgow Haskell Compiler Interactive) is
an interactive compiler. If you give it an expression, it will
evaluate it and then print the result to the screen. This kind of
software is sometimes called a REPL (Read Evaluate Print Loop),
because it reads your input, evaluates it, prints the result to the
screen, and then waits for more input so it can start the process all
over again in an infinite loop. From now on, we will just call it
ghci. To start it up, type
ghci in your console.
$ ghci GHCi, version 8.4.2: http://www.haskell.org/ghc/ :? for help Prelude>
Throughout this book, examples of input to ghci will be shown as lines
starting with a
> character. All text that follows on the same
line after this character is an input to ghci. The lines below it are
the ouput (the result of ghci evaluating your expression). With ghci
1 + 2 just like below, then hit the
> 1 + 2 3
:quit to exit ghci.
> :quit Leaving GHCi.