--- factorcss/FactorCSS.hs	2004/12/19 22:10:41	61
+++ factorcss/FactorCSS.hs	2004/12/27 19:11:07	62
@@ -1,3 +1,6 @@
+-- Factor a CSS stylesheet
+
+import List
 import Tokeniser
 import Parser
 import CSS
@@ -5,5 +8,96 @@
 main = do
 	s <- getContents
 --	print (alexScanTokens s)
---	print (parser (alexScanTokens s))
-	putStr (unlines (show_stylesheet (parser (alexScanTokens s))))
+--	(print . process . parser . alexScanTokens) s
+	(putStr . unlines . show_stylesheet . process .
+			parser . alexScanTokens) s
+
+-- Process a Stylesheet.
+process :: Stylesheet -> Stylesheet
+process (Stylesheet charset imports stmts) =
+		Stylesheet charset imports (process_stmts stmts)
+
+-- Process a list of Statements.
+process_stmts :: [Statement] -> [Statement]
+process_stmts stmts = (factor . filter is_ruleset) stmts ++
+		(map process_media . filter is_media) stmts ++
+		filter is_page stmts
+
+-- Process a Media Statement.
+process_media :: Statement -> Statement
+process_media (Media media stmts) = Media media (factor stmts)
+
+-- Factor a list of Ruleset Statements.
+factor :: [Statement] -> [Statement]
+factor = map implode_sel . groupBy eq_sel .
+		sortBy cmp_sel .
+		map implode_decl . groupBy eq_decl .
+		sortBy cmp_decl . sortBy cmp_sel .
+		concat . map explode
+
+-- Explode a Ruleset Statement into an equivalent list of Ruleset Statements
+-- with one Selector and one Declaration per Ruleset.
+--
+-- For example (in CSS syntax),
+--   explode "h1, em { color: red; background-color: blue }" =
+--       "h1 { color: red }
+--        h1 { background-color: blue }
+--        em { color: red }
+--        em { background-color: blue }"
+--
+-- [length (explode (Ruleset sels decls)) == length sels * length decls]
+explode :: Statement -> [Statement]
+explode (Ruleset sels decls) =
+		concat (map (\s -> map (\d -> Ruleset [s] [d]) decls) sels)
+
+-- Compare two Ruleset Statements by the Selectors in each.
+cmp_sel :: Statement -> Statement -> Ordering
+cmp_sel (Ruleset sels0 decls0) (Ruleset sels1 decls1)
+	| a < b		= LT
+	| a == b	= EQ
+	| a > b		= GT
+	where	a = show_selectors sels0
+		b = show_selectors sels1
+
+-- Compare two Ruleset Statements by the first Declaration in each.
+cmp_decl :: Statement -> Statement -> Ordering
+cmp_decl (Ruleset sels0 (decl0:decls0)) (Ruleset sels1 (decl1:decls1))
+	| a < b		= LT
+	| a == b	= EQ
+	| a > b		= GT
+	where	a = show_declaration decl0
+		b = show_declaration decl1
+
+-- Compare two Ruleset Statements for equality by the Selectors in each.
+eq_sel :: Statement -> Statement -> Bool
+eq_sel z = (== EQ) . cmp_sel z
+
+-- Compare two Ruleset Statements for equality by the first declaration in each.
+eq_decl :: Statement -> Statement -> Bool
+eq_decl z = (== EQ) . cmp_decl z
+
+-- Implode a list of Ruleset Statements with equal lists of Selectors to a
+-- single equivalent Ruleset Statement.
+--
+-- For example,
+--   implode_sel "h1, em { color: red }
+--        h1, em { background-color: blue }" =
+--       "h1, em { color: red; background-color: blue }"
+implode_sel :: [Statement] -> Statement
+implode_sel ((Ruleset sels decls):stmts) =
+		Ruleset sels (concat (decls:(map declarations stmts)))
+	where	declarations :: Statement -> [Declaration]
+		declarations (Ruleset s d) = d
+
+-- Implode a list of Ruleset Statements with equal lists of Declarations to a
+-- single equivalent Ruleset Statement.
+--
+-- For example,
+--   implode_decl "h1 { color: red }
+--        em { color: red }" =
+--       "h1, em { color: red }"
+implode_decl :: [Statement] -> Statement
+implode_decl ((Ruleset sels decls):stmts) =
+		Ruleset (concat (sels:(map selectors stmts))) decls
+	where	selectors :: Statement -> [Selector]
+		selectors (Ruleset s d) = s