Table of Contents
This section answers the question: "How do I include an Alex lexer in my program?"
Alex provides for a great deal of flexibility in how the
    lexer is exposed to the rest of the program.  For instance,
    there's no need to parse a String directly if
    you have some special character-buffer operations that avoid the
    overheads of ordinary Haskell Strings.  You
    might want Alex to keep track of the line and column number in the
    input text, or you might wish to do it yourself (perhaps you use a
    different tab width from the standard 8-columns, for
    example).
The general story is this: Alex provides a basic interface to the generated lexer (described in the next section), which you can use to parse tokens given an abstract input type with operations over it. You also have the option of including a wrapper, which provides a higher-level abstraction over the basic interface; Alex comes with several wrappers.
Lexer specifications are written in terms of Unicode characters, but Alex works internally on a UTF-8 encoded byte sequence.
        Depending on how you use Alex, the fact that Alex uses UTF-8
        encoding internally may or may not affect you.  If you use one
        of the wrappers (below) that takes input from a
        Haskell String, then the UTF-8 encoding is
        handled automatically.  However, if you take input from
        a ByteString, then it is your
        responsibility to ensure that the input is properly UTF-8
        encoded.
      
        None of this applies if you used the --latin1
        option to Alex or specify a Latin-1 encoding via a
        %encoding declaration.  In that case, the input is
        just a sequence of 8-bit bytes, interpreted as characters in the Latin-1
        character set.
      
The following (case-insenstive) encoding strings are currently supported:
%encoding "latin-1", %encoding "iso-8859-1"Declare Latin-1 encoding as described above.
%encoding "utf-8", %encoding "utf8"Declare UTF-8 encoding. This is
          the default encoding but it may be useful to explicitly declare
          this to make protect against Alex being called with the
          --latin1 flag.