Table of Contents
Haddock is invoked from the command line, like so:
haddock  [option...]  file... 
Where each file is a filename
    containing a Haskell source module (.hs) or a Literate Haskell source
    module (.lhs) or just a module name.
All the modules specified on the command line will be processed together. When one module refers to an entity in another module being processed, the documentation will link directly to that entity.
Entities that cannot be found, for example because they are in a module that isn't being processed as part of the current batch, simply won't be hyperlinked in the generated documentation. Haddock will emit warnings listing all the indentifiers it couldn't resolve.
The modules should not be mutually recursive, as Haddock don't like swimming in circles.
You must also specify an option for the output format.
    Currently only the -h option for HTML and the
    --hoogle option for outputting Hoogle data are
    functional.
The packaging tool Cabal has Haddock support, and is often used instead of invoking Haddock directly.
The following options are available:
-B dir
        Tell GHC that that its lib directory is
    dir. Can be used to override the default path.
-o dir
        , 
          
          --odir=dir
        Generate files into dir
	  instead of the current directory.
-l dir
        , 
	  
          --lib=dir
        Use Haddock auxiliary files (themes, javascript, etc...) in dir.
-i path,file
        , 
	  
          --read-interface=path,file
        Read the interface file in
	  file, which must have been
	  produced by running Haddock with the
	  --dump-interface option.  The interface
	  describes a set of modules whose HTML documentation is
	  located in path (which may be a
	  relative pathname).  The path is
	  optional, and defaults to “.”.
This option allows Haddock to produce separate sets of
	  documentation with hyperlinks between them.  The
	  path is used to direct hyperlinks
	  to point to the right files; so make sure you don't move the
	  HTML files later or these links will break.  Using a
	  relative path means that a
	  documentation subtree can still be moved around without
	  breaking links.
Multiple --read-interface options may
	  be given.
-D file
        , 
	  
          --dump-interface=file
        Produce an interface
	  file[1]
	  in the file file.  An interface
	  file contains information Haddock needs to produce more
	  documentation that refers to the modules currently being
	  processed - see the --read-interface option
	  for more details.  The interface file is in a binary format;
	  don't try to read it.
-h
        , 
	  
          --html
        Generate documentation in HTML format.  Several files
	  will be generated into the current directory (or the
	  specified directory if the -o option is
	  given), including the following:
module.htmlmini_module.htmlAn HTML page for each
		module, and a "mini" page for
		each used when viewing in frames.
index.htmlThe top level page of the documentation: lists the modules available, using indentation to represent the hierarchy if the modules are hierarchical.
doc-index.html, doc-index-X.htmlThe alphabetic index, possibly split into multiple pages if big enough.
frames.htmlThe top level document when viewing in frames.
some.cssetc...Files needed for the themes used. Specify your themes
		using the --theme option.
haddock-util.jsSome JavaScript utilities used to implement some of the dynamic features like collapsable sections, and switching to frames view.
--latex
        Generate documentation in LaTeX format.  Several files
          will be generated into the current directory (or the
            specified directory if the -o option is
            given), including the following:
package.texThe top-level LaTeX source file; to format the documentation into PDF you might run something like this:
$ pdflatex package.texhaddock.styThe default style.  The file contains
                definitions for various macros used in the LaTeX
                sources generated by Haddock; to change the way the
                formatted output looks, you might want to override
                these by specifying your own style with
                the --latex-style option.
module.texThe LaTeX documentation for
                each module.
--latex-style=style
        This option lets you override the default style used
            by the LaTeX generated by the --latex option.
            Normally Haddock puts a
            standard haddock.sty in the output
            directory, and includes the
            command \usepackage{haddock} in the
            LaTeX source.  If this option is given,
            then haddock.sty is not generated,
            and the command is
            instead \usepackage{.
          style}
-S
        , 
	  
          --docbook
        Reserved for future use (output documentation in DocBook XML format).
--source-base=URL
        , 
	  
          --source-module=URL
        , 
	  
          --source-entity=URL
        Include links to the source files in the generated
	  documentation. Use the --source-base option to add a
	  source code link in the header bar of the contents and index pages.
	  Use the --source-module to add a source code link in
	  the header bar of each module page. Use the
	  --source-entity option to add a source code link
	  next to the documentation for every value and type in each module.
	  
In each case URL is the base URL
	  where the source files can be found.  For the per-module and
	  per-entity URLs, the following substitutions are made within the
	  string URL:
The string %M or %{MODULE}
	      is replaced by the module name. Note that for the per-entity URLs
	      this is the name of the exporting module.
The string %F or %{FILE}
	      is replaced by the original source file name. Note that for the
	      per-entity URLs this is the name of the defining
	      module.
The string %N or %{NAME}
	      is replaced by the name of the exported value or type. This is
	      only valid for the --source-entity option.
The string %K or %{KIND}
	      is replaced by a flag indicating whether the exported name is a value
	      'v' or a type 't'. This is
	      only valid for the --source-entity option.
The string %L or %{LINE}
	      is replaced by the number of the line where the exported value or
	      type is defined. This is only valid for the
	      --source-entity option.
The string %% is replaced by
	      %.
For example, if your sources are online under some directory,
	  you would say
	  haddock --source-base=url/
	  --source-module=url/%F
If you have html versions of your sources online with anchors
	  for each type and function name, you would say
	  haddock --source-base=url/
	  --source-module=url/%M.html
	  --source-entity=url/%M.html#%N
For the %{MODULE} substitution you may want to
	  replace the '.' character in the module names with
	  some other character (some web servers are known to get confused by
	  multiple '.' characters in a file name). To
	  replace it with a character c use
	  %{MODULE/./.c}
Similarly, for the %{FILE} substitution
          you may want to replace the '/' character in
          the file names with some other character (especially for links
          to colourised entity source code with a shared css file).  To replace
          it with a character c use
          %{FILE////c}
One example of a tool that can generate syntax-highlighted HTML from your source code, complete with anchors suitable for use from haddock, is hscolour.
-s URL
        , 
	  
          --source=URL
        Deprecated aliases for --source-module
--comments-base=URL
        , 
	  
          --comments-module=URL
        , 
	  
          --comments-entity=URL
        Include links to pages where readers may comment on the documentation. This feature would typically be used in conjunction with a Wiki system.
Use the --comments-base option to add a
	  user comments link in the header bar of the contents and index pages.
	  Use the --comments-module to add a user comments
	  link in the header bar of each module page. Use the
	  --comments-entity option to add a comments link
	  next to the documentation for every value and type in each module.
	  
In each case URL is the base URL
	  where the corresponding comments page can be found.  For the
	  per-module and per-entity URLs the same substitutions are made as
	  with the --source-module and
	  --source-entity options above.
For example, if you want to link the contents page to a wiki
	  page, and every module to subpages, you would say
	  haddock --comments-base=url
	  --comments-module=url/%M
If your Wiki system doesn't like the '.' character
	  in Haskell module names, you can replace it with a different character. For
	  example to replace the '.' characters with
	  '_' use haddock
	  --comments-base=
	  Similarly, you can replace the 'url
	  --comments-module=url/%{MODULE/./_}/' in a file name (may
	  be useful for entity comments, but probably not.) 
--theme=path
        Specify a theme to be used for HTML (--html)
	  documentation. If given multiple times then the pages will use the
	  first theme given by default, and have alternate style sheets for
	  the others. The reader can switch between themes with browsers that
	  support alternate style sheets, or with the "Style" menu that gets 
	  added when the page is loaded. If
	  no themes are specified, then just the default built-in theme
	  ("Ocean") is used.
	  
The path parameter can be one of:
	  
A directory: The base name of
	      the directory becomes the name of the theme. The directory
	      must contain exactly one
	      some.csssome.css
A CSS file: The base name of the file becomes the name of the theme.
The name of a built-in theme ("Ocean" or "Classic").
--built-in-themes
        Includes the built-in themes ("Ocean" and "Classic").
	  Can be combined with --theme. Note that order
	  matters: The first specified theme will be the default.
-c file
        , 
	  
          --css=file
        Deprecated aliases for --theme
-p file
        , 
	  
          --prologue=file
        Specify a file containing documentation which is placed on the main contents page under the heading “Description”. The file is parsed as a normal Haddock doc comment (but the comment markers are not required).
-t title
        , 
          
          --title=title
        Use title as the page
	  heading for each page in the documentation.This will
	  normally be the name of the library being documented.
The title should be a plain string (no markup please!).
-q mode
        , 
          
          --qual=mode
        Specify how identifiers are qualified.
                mode should be one of
                
none (default): don't qualify any identifiers
full: always qualify identifiers completely
local: only qualify identifiers that are not part of the module
relative: like local, but strip name of the module from qualifications of identifiers in submodules
Example: If you generate documentation for module A, then the identifiers A.x, A.B.y and C.z are qualified as follows.
-?
        , 
          
          --help
        Display help and exit.
-V
        , 
          
          --version
        Output version information and exit.
-v
        , 
          
          --verbose
        Increase verbosity.  Currently this will cause Haddock
	  to emit some extra warnings, in particular about modules
	  which were imported but it had no information about (this is
	  often quite normal; for example when there is no information
	  about the Prelude).
--use-contents=URL
        , 
          
          --use-index=URL
        When generating HTML, do not generate an index.
	  Instead, redirect the Contents and/or Index link on each page to
	  URL.  This option is intended for
	  use in conjuction with --gen-contents and/or 
	  --gen-index for
	  generating a separate contents and/or index covering multiple
	  libraries.
--gen-contents
        , 
          
          --gen-index
        Generate an HTML contents and/or index containing entries pulled 
	  from all the specified interfaces (interfaces are specified using
	  -i or --read-interface).
	  This is used to generate a single contents and/or index for multiple 
	  sets of Haddock documentation.
--ignore-all-exports
	Causes Haddock to behaves as if every module has the
	    ignore-exports attribute (Section 3.7, “Module Attributes”).  This might be useful for
	    generating implementation documentation rather than interface
	    documentation, for example.
--hide module
	Causes Haddock to behaves as if module
	    module has the hide
	    atribute. (Section 3.7, “Module Attributes”).
--optghc=option
        Pass option to GHC.
-w
        , 
          
          --no-warnings
        Turn off all warnings.
--no-tmp-comp-dir
        
          Do not use a temporary directory for reading and writing compilation output files
          (.o, .hi, and stub files). Instead, use the
          present directory or another directory that you have explicitly told GHC to use
          via the --optghc flag.
          
This flag can be used to avoid recompilation if compilation files already exist. Compilation files are produced when Haddock has to process modules that make use of Template Haskell, in which case Haddock compiles the modules using the GHC API.
Since Haddock uses GHC internally, both plain and 
            literate Haskell sources are accepted without the need for the user
            to do anything. To use the C pre-processor, however,
            the user must pass the the -cpp option to GHC 
            using --optghc.
      
[1] Haddock interface files are not the same as Haskell interface files, I just couldn't think of a better name.