# diagrams-haddock
`diagrams-haddock` is a preprocessor which allows embedding images
generated using the [diagrams
framework](http://projects.haskell.org/diagrams/) within Haddock
documentation. The code to generate images is embedded directly
within the source file itself (and the code can be included in the
Haddock output or not, as you wish). `diagrams-haddock` takes care of
generating SVG images and linking them into the Haddock output.
## Installing
Just `cabal install diagrams-haddock`. If you have any trouble, ask
in the `#diagrams` freenode IRC channel, or file a ticket on the
[bug tracker](http://github.com/diagrams/diagrams-haddock/issues).
## On the design of `diagrams-haddock`
Before getting into the details of using `diagrams-haddock`, it should
be noted that `diagrams-haddock` has been carefully designed so that
*you only have to maintain a single copy of your source files*. In
particular, you do *not* have to maintain one copy of your source
files with embedded diagrams code and another copy where the diagrams
code has been replaced by images. If you find yourself scratching
your head over the quirky ways that `diagrams-haddock` works, now you
will know why.
## An important caveat
`diagrams-haddock` modifies files *in place*! While we have worked
hard to ensure that it cannot make catastrophic changes to your files,
you would be wise to **only run `diagrams-haddock` on files under
version control** so you can easily examine and (if necessary) undo
the changes it makes. (Of course, being a conscientious developer,
you would never work with source files not under version control,
right?)
## Adding diagrams to source files
Haddock supports inline links to images with the syntax `<<URL>>`. To
indicate an image which should be automatically generated from some
diagrams code, use the special syntax
`<<URL#diagram=name&key1=val1&key2=val2&...>>`. The URL will be
automatically filled in by `diagrams-haddock`, so when you first
create an inline image placeholder you can simply omit it (or put any
arbitrary text in its place). For example, you might write
<<#diagram=mySquare&width=200&height=300>>
indicating an image which should be generated using the definition of
`mySquare`, with a maximum width of 200 and maximum height of 300.
(Incidentally, this syntax is used because everything following the
`#` symbol will be ignored by browsers.)
Continuing with the above example, you must also provide a definition
of `mySquare`. You must provide it in a code block, which must be set
off by bird tracks (that is, greater-than symbols followed by at least
one space). For example,
``` haskell
-- > mySquare = square 1 # fc blue # myTransf
-- > myTransf = rotateBy (1/27)
```
You can choose to have the code block included in the Haddock output
or not, simply by putting it in a Haddock comment or not. Note that
the code block defining `mySquare` can be anywhere in the same file;
it does not have to be right before or right after the diagram URL
referencing it.
## Code block dependency analysis
`diagrams-haddock` does a simple dependency analysis to determine
which code blocks should be in scope while compiling each diagram.
First, it locates a code block containing a binding for the requested
diagram name. Then, it pulls in any code blocks containing bindings
for identifiers referenced by this code block, and so on transitively.
(Note that this analysis is overly simplistic and does not take things
like shadowing into account; this may sometimes cause additional code
blocks to be included which would not be included with a more careful
analysis.)
This has a few implications. First, code blocks containing irrelevant
bindings will not be considered. It is common to have code blocks
which are intended simply to show some example code---they may not
even be valid Haskell. However, as long as such code blocks do not
contain any bindings of names used by a diagram, they will be ignored.
For example:
``` haskell
-- The algorithm works by doing the equivalent of
--
-- > rep = uncurry replicate
-- >
-- > algo = map rep . zip [1..]
--
-- as illustrated below:
--
-- <<#diagram=algoIllustration&width=400>>
--
-- > algoIllustration = ...
```
The first code block shown above (beginning `rep = ...`) contains some
bindings, but none of those bindings are referenced by any diagram
URLs, so the code block is ignored.
Another convenient implication is that supporting code can be put in
separate code blocks and even shared between diagrams. For example:
``` haskell
-- > makeitblue d = d # fc blue # lc blue
--
-- Here is a blue circle:
--
-- <<#diagram=blueC&width=200>>
--
-- > blueC = circle 1 # makeitblue
--
-- And here is a blue square:
--
-- <<#diagram=blueS&width=200>>
--
-- > blueS = square 1 # makeitblue
```
This also means that diagrams are recompiled only when necessary. For
example, if the definition of `blueC` is changed, only `blueC` will be
recompiled. If the definition of `makeitblue` is changed, both
`blueC` and `blueS` will be recompiled.
## Invoking diagrams-haddock
Invoking the `diagrams-haddock` tool is simple: just give it a
list of targets, like so:
```
diagrams-haddock foo.hs baz/bar.lhs ~/src/some-cabal-directory
```
* For file targets, `diagrams-haddock` simply processes the given file.
* Directory targets are assumed to contain Cabal packages, which
themselves contain a library. `diagrams-haddock` then finds and
processes the source files corresponding to all modules exported by
the library. (Note that `diagrams-haddock` does not currently run on
unexported modules or on the source code for executables, but if you
have a use case for either, just file a [feature
request](https://github.com/diagrams/diagrams-haddock/issues); they
shouldn't be too hard to add.)
Also, if you simply invoke `diagrams-haddock` with no targets, it will
process the Cabal package in the current directory.
`diagrams-haddock` also takes a few command-line options which can be
used to customize its behavior:
* `-c`, `--cachedir`: When diagrams are compiled, their source code is
hashed and the output image stored in a file like `068fe.......342.svg`,
with the value of the hash as the name of the file. This way, if
the source code for a diagram has not changed in between invocations
of `diagrams-haddock`, it does not need to be recompiled. This
option lets you specify the directory where such cached SVG files
should be stored; the default is `.diagrams-cache`.
* `-o`, `--outputdir`: This is the directory into which the final
output images will be produced. The default is `diagrams`.
* `-d`, `--distdir`: When building diagrams for a cabal package, this
is the directory in which `diagrams-haddock` should look for the
`setup-config` file (*i.e.* the output of `cabal configure`). An
explicit value for this flag takes precedence; next,
`diagrams-haddock` checks whether there is an active
[hsenv](http://hackage.haskell.org/package/hsenv) environment, and
if so uses `dist_<hsenv name>`; otherwise, it defaults to using
`dist`.
* `-i`, `--includedirs`: `diagrams-haddock` does its best to process
files with CPP directives, even extracting information about where
to find `#include`s from the `.cabal` file, but sometimes it might
need a little help. This option lets you specify additional
directories in which `diagrams-haddock` should look when searching
for `#include`d files.
* `--cppdefines`: likewise, this option allows you to specify
additional names that should be `#define`d when CPP is run.
* `--dataURIs`: embed the generated SVG images directly in the source
code with [data URIs](http://en.wikipedia.org/wiki/Data_URI_scheme)
(the default is to generate external SVG files and link to them).
See the section below for a discussion of the tradeoffs involved.
* `-q`, `--quiet`: `diagrams-haddock` normally prints some logging
information to indicate what it is doing; this option silences the
output.
## Workflow and Cabal setup
There are two ways one may include generated SVG images with your
documentation: as data URIs, or as external images. The two options
are discussed below, along with pros and cons of each. Note that in
either case, consumers of your library (including Hackage itself) do
*not* need to have `diagrams-haddock` installed in order to build your
documentation.
### Using data URIs
If you pass the `--dataURIs` option to `diagrams-haddock`, any
generated images will be embedded directly in your source file (and
hence also in the HTML ultimately produced by `haddock`) as
[data URIs](http://en.wikipedia.org/wiki/Data_URI_scheme). To use
this method,
1. Include inline diagrams code and URLs in your source code.
2. Run `diagrams-haddock --dataURIs`.
3. Commit the resulting URL changes to your source files.
The benefit of this scheme is that there are no extra files to deal
with, and no need to alter your `.cabal` file in any way. The
downside is that it significantly bloats your source code, and may
make it extremely inconvenient to edit without some sort of tool
support (*e.g.* an editor that can "collapse" certain sections of the
source file).
### Using external images
By default, `diagrams-haddock` generates external SVG image files. This
makes for a much less invasive changes to your source files, but
requires some extra work to manage the extra files. To use this method,
1. Include inline diagrams code and URLs in your source code.
2. Run `diagrams-haddock`.
3. Commit the resulting URL changes to your source files *and* the produced SVG files.
4. Arrange to have the SVG files installed along with your package's
Haddock documentation (more on this below).
The generated SVG files need to be copied alongside the generated
Haddock documentation. There are two good ways to accomplish this:
1. The `cabal` tool has recently acquired an `extra-doc-files` field
(see https://github.com/haskell/cabal/pull/1182 and
https://github.com/haskell/cabal/pull/1427), specifying files
which should be copied in alongside generated Haddock
documentation. So you could simply write something like
```
extra-doc-files: diagrams/*.svg
```
in your `.cabal` file. Unfortunately, it will still be a while
until this feature makes its way into a new release of `cabal`,
and yet longer before you can be sure that most people who may
want to build your package's documentation have the new version.
So this is currently a good option only if you have the HEAD
version of `cabal` and don't care about others being able to
build your documentation. However, in the not-too-distant future
this will become the best option.
2. In the meantime, it is possible to take advantage of `cabal`'s
system of user hooks to manually copy the images right after the
Haddock documentation is generated. Add something like
```
build-type: Custom
extra-source-files: diagrams/*.svg
```
to your `.cabal` file, and then put something like the following in your
`Setup.hs`:
``` haskell
import Data.List (isSuffixOf)
import Distribution.Simple
import Distribution.Simple.Setup (Flag (..), HaddockFlags,
haddockDistPref)
import Distribution.Simple.Utils (copyFiles)
import Distribution.Text (display)
import Distribution.Verbosity (normal)
import System.Directory (getDirectoryContents)
import System.FilePath ((</>))
-- Ugly hack, logic copied from Distribution.Simple.Haddock
haddockOutputDir :: Package pkg => HaddockFlags -> pkg -> FilePath
haddockOutputDir flags pkg = destDir
where
baseDir = case haddockDistPref flags of
NoFlag -> "."
Flag x -> x
destDir = baseDir </> "doc" </> "html" </> display (packageName pkg)
diagramsDir = "diagrams"
main :: IO ()
main = defaultMainWithHooks simpleUserHooks
{ postHaddock = \args flags pkg lbi -> do
dias <- filter ("svg" `isSuffixOf`) `fmap` getDirectoryContents diagramsDir
copyFiles normal (haddockOutputDir flags pkg)
(map (\d -> ("", diagramsDir </> d)) dias)
postHaddock simpleUserHooks args flags pkg lbi
}
```
It may not be pretty, but it works!
## File encodings
For now, `diagrams-haddock` assumes that all `.hs` and `.lhs` files
are encoded using UTF-8. If you would like to use it with source
files stored using some other encoding, feel free to [file a feature
request](https://github.com/diagrams/diagrams-haddock/issues).
## The diagrams-haddock library
For most use cases, simply using the `diagrams-haddock` executable
should get you what you want. Note, however, that the internals are
also exposed as a library, making it possible to do all sorts of crazy
stuff you might dream up. Let us know what you do with it!
## Reporting bugs
Please report any bugs, feature requests, *etc.*, on the [github issue
tracker](https://github.com/diagrams/diagrams-haddock/issues).