Removed plugin support.

Plugins will probably be added in a later version,
but for now we want to avoid the heavy GHC API dependency.
Also, plugins are very slow with the current system.

git-svn-id: https://pandoc.googlecode.com/svn/trunk@1548 788f1e2b-df1e-0410-8736-df70ead52e1b

1 files changed, 0 insertions, 217 deletions

diff --git a/README b/README
index d2bc5ce65..96deb6dd5 100644
--- a/README
+++ b/README
@@ -309,14 +309,6 @@ For further documentation, see the `pandoc(1)` man page.
     repeatedly to include multiple files. They will be included in the
     order specified.
 
-`-P` *MODULE[,MODULE...]*, `--plugins`*=MODULE[,MODULE...]*
-:   specifies plugins to load, by module name or source file pathname.
-    Plugins should export a function `transform` of type `a -> a`
-    or `a -> IO a`, where `a` is `Inline`, `Block`, `Pandoc`,
-    `[Inline]`, or `[Block]`.  This function will be used to transform
-    the pandoc document after it is parsed by the reader and before it
-    is written out by the writer.  (See below on [Plugins](#plugins).)
-
 `-T` or `--title-prefix` *string*
 :   includes *string* as a prefix at the beginning of the title that
     appears in the HTML header (but not in the title as it appears at
@@ -1124,212 +1116,3 @@ ordinary HTML (without bird tracks).
 writes HTML with the Haskell code in bird tracks, so it can be copied
 and pasted as literate Haskell source.
 
-Plugins
-=======
-
-Pandoc's plugin system allows users to modify pandoc's behavior by writing
-short Haskell programs.  To how this works, and why it is useful, we
- need to understand that pandoc transforms one format (the source
-format) into another (the target format) by first converting from the
-source format into a Haskell data structure representing the document,
-and then converting this data structure into the target format. For
-example:
-
- -------------------------------------------------------------------------------
-   Document     Format                       Contents
- ------------  ---------   -----------------------------------------------------
-     source     markdown                 `Hello *world*.`
-
-       ↓           ↓                            ↓
-
- intermediate    native               `Pandoc (Meta [] [] "")
-                           [Para [Str "Hello",Space,Emph [Str "world"],Str "."]]`
-
-       ↓           ↓                            ↓
-
-     target       HTML               `<p>Hello <em>world</em>.</p>`
- -------------------------------------------------------------------------------
-
-We can use standard text-processing tools (`perl`, `sed`, `awk`, etc.)
-to modify the source or target documents.  But what if we want to modify
-the intermediate representation -- the parsed document -- before it is
-written to the target format? That's where plugins are needed.
-A plugin is a Haskell module that exports a function `transform`, which
-will be used to transform the native representation, after it is generated
-by the reader, but before it has been transformed by the writer.
-
-An example will help make this clearer.  Suppose we want to use pandoc with
-the WordPress blog engine.  WordPress provides support for LaTeX math, but
-instead of `$e = mc^2$`, WordPress wants `$LaTeX e = mc^2$`.  Prior to plugins,
-there was no good way to make pandoc do this.  We could have tried using
-regex replacements on the markdown input or HTML output, but this would have
-been error-prone:  if someone writes `$e = mc^2$` in a code block, for
-example, we wouldn't want to insert `LaTeX` there.  There's no good way to
-identify the math chunks without parsing the whole document. And pandoc
-is already doing that, so why not make use of this work? By writing a
-plugin, we can.  Here's the whole plugin:
-
-~~~ {.haskell}
--- WordPressPlugin.hs
-module WordPressPlugin (transform) where
-import Text.Pandoc
-
-transform :: Inline -> Inline
-transform (Math x y) = Math x $ "LaTeX " ++ y
-transform x          = x
-~~~
-
-This is a Haskell program, but a very short one. The lines
-
-~~~ {.haskell}
-module WordPressPlugin (transform) where
-import Text.Pandoc
-~~~
-
-just define the name of the module (`WordPressPlugin`), the names of any
-exported functions (for a plugin, this will always just be `transform`),
-and the modules that will be used in the program itself (`Text.Pandoc`).
-Every plugin must export a function named `transform`.
-
-The real meat of the program is the three-line definition of `transform`:
-
-~~~ {.haskell}
-transform :: Inline -> Inline
-transform (Math x y) = Math x $ "LaTeX " ++ y
-transform x          = x
-~~~
-
-The first line defines the type of the function:  it is a function that
-takes an `Inline` element and returns an `Inline` element.  (For the definition
-of `Inline`, see the module `Text.Pandoc.Definition`.)  The `transform`
-function in a plugin need not be `Inline -> Inline`, but it must have
-type `a -> a` or `a -> IO a`, where `a` is `Pandoc`, `Block`, `Inline`,
-`[Block]`, or `[Inline]`.
-
-The next line says that when the input matches the pattern `Math x y`,
-the string `LaTeX ` should be inserted at the beginning of `y`. (The `x`
-just specifies whether the math element is inline or display math, so
-we leave it alone.) The last line says, in effect, that the `transform`
-function has no effect on any other kind of `Inline` element -- it just
-passes it through. When the plugin is applied, this transformation will
-be used on every `Inline` element in the document, and `LaTeX ` will be
-inserted where needed in math elements.
-
-To use this plugin, we just specify the module (or alternatively the filename)
-with the `--plugins` option:
-
-    % echo "Hello, $e=mc^2$." | pandoc -m --plugins=WordPressPlugin.hs
-    <p
-    >Hello, <span class="LaTeX"
-      >$LaTeX e=mc^2$</span
-      >.</p
-    >
-
-Let's look at a more complex example, involving IO.  Suppose we want to include
-some [graphviz](http://www.graphviz.org/) diagrams in our document.
-Of course, we could use a Makefile to generate the diagrams, then use
-regular images in our document. But wouldn't it be nicer just to include
-the graphviz code in the document itself, perhaps in a specially marked
-delimited code block?
-
-    ~~~ {.dot name="diagram1"}
-    graph G {
-      e
-      subgraph clusterA {
-        a -- b;
-        subgraph clusterC {
-          C -- D;
-        }
-      }
-      subgraph clusterB {
-        d -- f
-      }
-      d -- D
-      e -- clusterB
-      clusterC -- clusterB
-    }
-    ~~~
- 
-This can be accomplished by a plugin:
-
-~~~ {.haskell}
--- DotPlugin.hs
-module DotPlugin (transform) where
-import Text.Pandoc
-import Text.Pandoc.Shared
-import System.Process (readProcess)
-import Data.Char (ord)
--- from the utf8-string package on HackageDB:
-import Data.ByteString.Lazy.UTF8 (fromString)
--- from the SHA package on HackageDB:
-import Data.Digest.Pure.SHA
-
-transform :: Block -> IO Block
-transform (CodeBlock (id, classes, namevals) contents) | "dot" `elem` classes = do
-  let (name, outfile) =  case lookup "name" namevals of
-                                Just fn   -> ([Str fn], fn ++ ".png")
-                                Nothing   -> ([], uniqueName contents ++ ".png")
-  result <- readProcess "dot" ["-Tpng"] contents
-  writeFile outfile result
-  return $ Para [Image name (outfile, "")]
-transform x = return x
-
--- | Generate a unique filename given the file's contents.
-uniqueName :: String -> String
-uniqueName = showDigest . sha1 . fromString
-~~~
-
-The heart of this plugin is the `transform` function, which converts a `Block`
-to a `Block`.  Again, there are two clauses, one for code blocks that are marked
-with the "dot" class, one for all other blocks.  Code blocks with ".dot" are
-replaced with links to an image file; this file is generated by running
-`dot -Tpng` on the contents of the code block.
-
-Because `transform` performs file reads and writes, it needs to be in the
-IO monad, hence the type: `Block -> IO Block`.
-
-One more example.  Suppose we want emphasized text to be CAPITALIZED
-instead of italicized.  We could use a plugin:
-
-~~~ {.haskell}
-module CapitalizeEmphasisPlugin (transform) where
-import Text.Pandoc
-import Data.Char (toUpper)
-
-transform :: [Inline] -> [Inline]
-transform (Emph xs : ys) = processWith capStr xs ++ transform ys
-transform (x : ys)       = x : transform ys
-transform []             = []
-
-capStr :: Inline -> Inline
-capStr (Str x) = Str (map toUpper x)
-capStr x       = x
-~~~
-
-Here `transform` converts a whole list of `Inline` elements to another
-such list.  The key clause is
-
-~~~ {.haskell}
-transform (Emph xs : ys) = processWith capStr xs ++ transform ys
-~~~
-
-This applies the `capStr` function recursively to all inlines in the
-list of emphasized inlines and puts the transformed list in place
-of the original.  `capStr` is a simple `Inline` transformation that
-capitalizes `Str` elements and leaves everything else alone.  The
-function `processWith`, defined in `Text.Pandoc.Definition`, uses some
-`Data.Generics` magic to apply its argument (here `capStr`) to every
-`Inline` element in a list, including elements that are deeply buried in
-other elements. Thus
-
-    processWith captStr [Str "one", Strong [Str "two", Space]] ==>
-    [Str "ONE", Strong [Str "TWO", Space]]
-
-There are other sample plugins in the `plugins` subdirectory of the
-pandoc source code.
-
-**Note:**  Do not attempt to use plugins when running pandoc in the
-directory containing pandoc's source code.  The interpreter will try to
-load the files directly from the source code, rather than reading the compiled
-versions, and pandoc will hang.
-