Added templates module.

git-svn-id: https://pandoc.googlecode.com/svn/trunk@1673 788f1e2b-df1e-0410-8736-df70ead52e1b

pandoc.cabal

@@ -193,6 +193,7 @@ Library
                    Text.Pandoc.Writers.S5
   Other-Modules:   Text.Pandoc.XML,
                    Text.Pandoc.TH,
+                   Text.Pandoc.Templates
                    Paths_pandoc
   Extensions:      CPP, TemplateHaskell, FlexibleInstances
   Ghc-Options:     -O2 -Wall

src/Text/Pandoc/Templates.hs

@@ -0,0 +1,111 @@
+{-
+Copyright (C) 2009 John MacFarlane <jgm@berkeley.edu>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+-}
+
+{- |
+   Module      : Text.Pandoc.Templates
+   Copyright   : Copyright (C) 2009 John MacFarlane
+   License     : GNU GPL, version 2 or above
+
+   Maintainer  : John MacFarlane <jgm@berkeley.edu>
+   Stability   : alpha
+   Portability : portable
+
+A simple templating system with variable substitution and conditionals.
+Example:
+
+> > renderTemplate [("name","Sam"),("salary","50,000")] $
+>   "Hi, $name$.  $if(salary)$You make $$$salary$.$else$No salary data.$endif$" 
+> > "Hi, John.  You make $50,000."
+
+A slot for an interpolated variable is a variable name surrounded
+by dollar signs.  To include a literal @$@ in your template, use
+@$$@.  Variable names must begin with a letter and can contain letters,
+numbers, @_@, and @-@.
+
+A conditional begins with @$if(variable_name)$@ and ends with @$endif$@.
+It may optionally contain an @$else$@ section.  The if section is
+used if @variable_name@ has a non-null value, otherwise the else section
+is used.
+-}
+
+module Text.Pandoc.Templates (renderTemplate) where
+
+import Text.ParserCombinators.Parsec
+import Control.Monad (liftM)
+
+-- | Renders a template 
+renderTemplate :: [(String,String)]  -- ^ Assoc. list of values for variables
+               -> String             -- ^ Template
+               -> String
+renderTemplate vals templ =
+  case runParser (do x <- parseTemplate; eof; return x) vals "template" templ of
+       Left e        -> show e
+       Right r       -> concat r
+
+reservedWords :: [String]
+reservedWords = ["else","endif"]
+
+parseTemplate :: GenParser Char [(String,String)] [String]
+parseTemplate =
+  many $ plaintext <|> escapedDollar <|> conditional <|> variable
+
+plaintext :: GenParser Char [(String,String)] String
+plaintext = many1 $ satisfy (/='$')
+
+escapedDollar :: GenParser Char [(String,String)] String
+escapedDollar = try $ string "$$" >> return "$"
+
+conditional :: GenParser Char [(String,String)] String
+conditional = try $ do
+  string "$if("
+  id' <- ident
+  string ")$"
+  skipMany (oneOf " \t")
+  optional newline
+  ifContents <- liftM concat parseTemplate
+  elseContents <- option "" $ do try (string "$else$")
+                                 skipMany (oneOf " \t")
+                                 optional newline
+                                 liftM concat parseTemplate
+  string "$endif$"
+  skipMany (oneOf " \t")
+  optional newline
+  st <- getState
+  return $ case lookup id' st of
+             Just ""  -> elseContents
+             Just _   -> ifContents
+             Nothing  -> elseContents
+
+ident :: GenParser Char [(String,String)] String
+ident = do
+  first <- letter
+  rest <- many (alphaNum <|> oneOf "_-")
+  let id' = first : rest
+  if id' `elem` reservedWords
+     then pzero
+     else return id'
+
+variable :: GenParser Char [(String,String)] String
+variable = try $ do
+  char '$'
+  id' <- ident
+  char '$'
+  st <- getState
+  return $ case lookup id' st of
+           Just val  -> val
+           Nothing   -> ""