* haddorg-api

*NOTE*. This is the README file to ~haddorg-api~.  For the README file
to haddock, see README.md.

** Overview

Haddock is a documentation generator for Haskell libraries and it
supports several backends including HTML, latex and hoogle.  The
program logic of the ~haddock~ tool is the ~haddock-api~ package.

~haddorg-api~ adds an org backend of ~haddock-api~, so that one can
invoke haddock to generate org files, of the Org Mode.

** Examples

- [[https://ypei.org/assets/haddorg-output/base-4.16.1.0.org.gz][base-4.16.1.0.org]]
- [[https://ypei.org/assets/haddorg-output/ghc-lib-parser-9.2.2.20220307.org.gz][ghc-lib-parser-9.2.2.20220307.org]], which can be used as a fake ghc
  for cross-package linking
- lens
- [[https://ypei.org/assets/haddorg-output/haddorg-api-2.26.1.org.gz][haddorg-api-2.26.1.org]], also in this repository
- [[https://ypei.org/assets/haddorg-output/haddock-library-2.26.1.org.gz][haddock-library-2.26.1.org]]
- [[https://ypei.org/assets/haddorg-output/haddorg-ghc-base.org.gz][haddorg-api + haddock-library + fake ghc + base]], demonstrating
  cross-package linking
- [[https://ypei.org/assets/haddorg-output/fsd-sqlite-simple-debian.org.gz][fsd + sqlite-simple + debian]], to demonstrating cross-package linking
- and [[https://ypei.org/assets/haddorg-output/][more...]]

** Install

#+begin_src sh
git clone https://g.ypei.me/haddock.git
cd haddock
cabal install
#+end_src

This will create a haddock binary under ~$HOME/.cabal/bin~ - make sure
it is in your PATH.

To make cabal use the haddock built with ~haddorg-api~, modify the
~haddock-ghc-x.y.z~ shell script, where ~x.y.z~ is the GHC version.

The file ~haddock-ghc-x.y.z~ is located in the same directory as your
~ghc-x.y.z~ binary.  The following command should print its path

#+begin_src sh
readlink -f `which ghc` | sed 's/\(.*\)ghc\(.*\)/\1haddock-ghc\2/'
#+end_src

For example, if you use ghcup and ghc-9.2.2, then the path should be
~$HOME/.ghcup/ghc/9.2.2/bin/haddock-ghc-9.2.2~.

Once you have located the correct ~haddock-ghc~ script, modify it by
updating the ~exedir~ to ~"$HOME/.cabal/bin"~:

#+begin_src sh
#!/bin/sh
exedir="$HOME/.cabal/bin" # <- update this line
exeprog="haddock"
# ...
#+end_src

** Usage

~haddorg-api~ adds an ~--org~ flag to the ~haddock~ command.

*** Direct invocation

#+begin_src sh
haddock Hello.hs --org
#+end_src

*** With cabal
After telling cabal to use haddock built with haddorg-api (see
[[Install]]), cd into the package you want to build the org documentation
for, and run:

#+begin_src sh
cabal haddock --haddock-option=--org
#+end_src

If success, a fresh new org documentation will be placed under the
package directory.

** Tips

- If you would like cross-package links to work, simply concatenate
  files.  For example, concat the org file of base with that of any
  library that say uses ~String~ in ~Prelude~ will cause ~String~
  links to navigate to the definition of ~String~.

** Coverage and areas for further work

Most features and most packages should work.  However, there are some
features to be completed.  Below is an incomplete list of missing
features, with rare occurrences in real world haskell documentations
marked by (RARE)

- Infix declarations (currently all infix decls are shown as prefix)
- Operator precendences
- Minimal Signatures for classes operations
- Correct linking due to distinction between top level identifiers and
  constructors
- (RARE) Data instance constructors
- (RARE) Linear types
- (RARE) Bundled patterns

Some (rare) problems due to mismatch of haddock markup and org mode:

- (RARE) Lack of distinction between inline and block elements in
  haddock markup
- (RARE) Table column and row spans

Some cosmetic issues:

- Relative heading depth for DocHeaders

*** Linking issue

One classical question for Org Mode users is: One org file per package
or one big org file containing all packages?  Currently haddorg-api
takes the latter approach.  It produces one org file per package, but
cross-package links are generated in a way so that they only work in
one big org file from concatenation of separate package org
files. This may become unwieldy, especially when the big org file
contains large libraries like base and ghc.  For links to work in the
alternative approach, the links have to be aware of org files of other
packages.

** Acknowledgement

Part of the code is adapted from [[https://github.com/lucasvreis/org-parser][org-parser]].

** License, copyright, contributing

Haddock is licensed under modified BSD (aka BSD-3-Clause), with
haddock-api and haddock-library licensed under the FreeBSD license
(aka BSD 2-Clause).  To contribute, see CONTRIBUTING.md.

The Org backend written by Yuchen Pei is under the GNU Affero General
Public License, version 3 or later.  See COPYING.agpl3 for the license
text.  To report issues or send patches regarding the org backend,
email Yuchen at <id@ypei.org>.