1 files changed, 66 insertions, 0 deletions
diff --git a/src/Text/Hakyll/Regex.hs b/src/Text/Hakyll/Regex.hs
new file mode 100644
index 0000000..e2e21bc
--- /dev/null
+++ b/src/Text/Hakyll/Regex.hs
@@ -0,0 +1,66 @@
+-- | A module that exports a simple regex interface. This code is mostly copied
+--   from the regex-compat package at hackage.
+module Text.Hakyll.Regex
+    ( split
+    , substitute
+    ) where
+
+import Text.Regex.TDFA
+
+-- | Match a regular expression against a string, returning more information
+--   about the match.
+matchRegexAll :: Regex -> String -> Maybe (String, String, String, [String])
+matchRegexAll p str = matchM p str
+
+-- | Replaces every occurance of the given regexp with the replacement string.
+subRegex :: Regex                          -- ^ Search pattern
+      -> String                         -- ^ Input string
+      -> String                         -- ^ Replacement text
+      -> String                         -- ^ Output string
+subRegex _ "" _ = ""
+subRegex regexp inp replacement =
+  let -- bre matches a backslash then capture either a backslash or some digits
+      bre = makeRegex "\\\\(\\\\|[0-9]+)"
+      lookup' _ [] _ = []
+      lookup' [] _ _ = []
+      lookup' match' repl groups =
+        case matchRegexAll bre repl of
+          Nothing -> repl
+          Just (lead, _, trail, bgroups) ->
+            let newval =
+                 if (head bgroups) == "\\"
+                   then "\\"
+                   else let index :: Int
+                            index = (read (head bgroups)) - 1
+                        in if index == -1
+                             then match'
+                             else groups !! index
+            in lead ++ newval ++ lookup' match' trail groups
+  in case matchRegexAll regexp inp of
+       Nothing -> inp
+       Just (lead, match', trail, groups) ->
+         lead ++ lookup' match' replacement groups ++ (subRegex regexp trail replacement)
+
+-- | Splits a string based on a regular expression.  The regular expression
+--   should identify one delimiter.
+splitRegex :: Regex -> String -> [String]
+splitRegex _ [] = []
+splitRegex delim strIn = loop strIn where
+  loop str = case matchOnceText delim str of
+                Nothing -> [str]
+                Just (firstline, _, remainder) ->
+                  if null remainder
+                    then [firstline,""]
+                    else firstline : loop remainder
+
+-- | Split a list at a certain element.
+split :: String -> String -> [String]
+split pattern = filter (not . null)
+              . splitRegex (makeRegex pattern)
+
+-- | Substitute a regex. Simplified interface.
+substitute :: String -- ^ Pattern to replace (regex).
+           -> String -- ^ Replacement string.
+           -> String -- ^ Input string.
+           -> String -- ^ Result.
+substitute pattern replacement str = subRegex (makeRegex pattern) str replacement