main = do doc <- here "DATA" "Here.hs" [("variable","some"),("substitution","variables")] putStrLn doc html <- here "HTML" "Here.hs" [("code",doc)] putStrLn html here tag file env = do txt <- readFile file let (_,_:rest) = span (/="{- "++tag++" START") (lines txt) (doc,_) = span (/=" "++tag++" END -}") rest return $ unlines $ map subst doc where subst ('$':'(':cs) = case span (/=')') cs of (var,')':cs) -> maybe ("$("++var++")") id (lookup var env) ++ subst cs _ -> '$':'(':subst cs subst (c:cs) = c:subst cs subst "" = "" {- DATA START this is a poor man's here-document with quotes ", and escapes \, and line-breaks, and layout without escaping \" \\ \n, without concatenation. oh, and with $(variable) $(substitution), $(too). DATA END -} {- HTML START very important page $(code) HTML END -}