I am somewhat new to haskell. It is amazing that I can actually write a CGI program using Network.CGI without really being comfortable with the Haskell type system. Especially when it involves monad transformations. So I decided that I better understand this. I looked at the Practical Web Programming examples to try to understand what is going on. I came up with a problem that might demonstrate my misunderstanding. I am wondering if you can answer questions I have. Code 1 is the example from PWP, Code 2 is my variation and it works so I am stumped by what the liftM is required. code 1>>> #!/usr/bin/runghc import Network.CGI import Text.XHtml import qualified Data.ByteString.Lazy as BS import Control.Monad (liftM) import Data.Maybe (fromJust) uploadDir = "../upload" fileForm = form ! [method "post", enctype "multipart/form-data"] << [afile "file", submit "" "Upload"] saveFile n = do cont <- (liftM fromJust) $ getInputFPS "file" let f = uploadDir ++ "/" ++ basename n liftIO $ BS.writeFile f cont return $ paragraph << ("Saved as " +++ anchor ! [href f] << f +++ ".") page t b = header << thetitle << t +++ body << b basename = reverse . takeWhile (`notElem` "/\\") . reverse cgiMain = do mn <- getInputFilename "file" h <- maybe (return fileForm) saveFile mn output $ renderHtml $ page "Upload example" h main = runCGI $ handleErrors cgiMain Code 2 (modifier) >>> import Network.CGI import Text.XHtml import qualified Data.ByteString.Lazy as BS import Control.Monad (liftM) import Data.Maybe (fromJust) uploadDir = "../upload" fileForm = form ! [method "post", enctype "multipart/form-data"] << [afile "file", submit "" "Upload"] saveFile n = do cont <- getInputFPS "file" let f = uploadDir ++ "/" ++ basename n liftIO $ BS.writeFile f (fromJust cont) return $ paragraph << ("Saved as " +++ anchor ! [href f] << f +++ ".") page t b = header << thetitle << t +++ body << b basename = reverse . takeWhile (`notElem` "/\\") . reverse cgiMain = do mn <- getInputFilename "file" h <- maybe (return fileForm) saveFile mn output $ renderHtml $ page "Upload example" h main = runCGI $ handleErrors cgiMain Questions === 1) Why did the author choose to insert "liftM" in function saveFile? It doesn't seem necessary in my version. 2) My background mainly is Java but here is my understanding of Monad Transforms. The CGIT m type carries around with it the CGI Request context and response contexts. The transformations (lifts) is similar to casting so that you can use the functions for specific manifestations but it also encapsulates the data. Is this correct? Edward