Simplify guess functions

Author: BasLaa

cabal-install/src/Distribution/Client/Init/Interactive/Command.hs

@@ -355,14 +355,10 @@ licensePrompt flags = getLicense flags $ do
       else fmap prettyShow knownLicenses
 
 authorPrompt :: Interactive m => InitFlags -> m String
-authorPrompt flags = getAuthor flags $ do
-    name <- guessAuthorName
-    promptOrDefault name "Author name"
+authorPrompt flags = getAuthor flags $ guessAuthorName >>= promptOrDefault "Author name"
 
 emailPrompt :: Interactive m => InitFlags -> m String
-emailPrompt flags = getEmail flags $ do
-    email' <- guessAuthorEmail
-    promptOrDefault email' "Maintainer email"
+emailPrompt flags = getEmail flags $ guessAuthorEmail >>= promptOrDefault "Maintainer email"
 
 homepagePrompt :: Interactive m => InitFlags -> m String
 homepagePrompt flags = getHomepage flags $
@@ -468,7 +464,5 @@ srcDirsPrompt flags = getSrcDirs flags $ do
 
     return [dir]
 
-promptOrDefault :: Interactive m => Maybe String -> String -> m String
-promptOrDefault m s = case m of
-  Nothing -> promptStr s MandatoryPrompt
-  Just d  -> promptStr s (DefaultPrompt d)
+promptOrDefault :: Interactive m => String -> Maybe String -> m String
+promptOrDefault s = maybe (promptStr s MandatoryPrompt)  (promptStr s . DefaultPrompt)

cabal-install/src/Distribution/Client/Init/NonInteractive/Command.hs

@@ -276,20 +276,14 @@ licenseHeuristics flags = getLicense flags $ guessLicense flags
 -- | The author's name. Prompt, or try to guess from an existing
 --   git repo.
 authorHeuristics :: Interactive m => InitFlags -> m String
-authorHeuristics flags = do
-  email' <- guessAuthorEmail
-  case email' of
-    Just n  -> getAuthor flags $ return n
-    Nothing -> getAuthor flags $ return ""
+authorHeuristics flags = guessAuthorEmail >>=
+  maybe (getAuthor flags $ return "") (getAuthor flags . return)
 
 -- | The author's email. Prompt, or try to guess from an existing
 --   git repo.
 emailHeuristics :: Interactive m => InitFlags -> m String
-emailHeuristics flags = do
-  name' <- guessAuthorName
-  case name' of
-    Just n  -> getEmail flags $ return n
-    Nothing -> getEmail flags $ return ""
+emailHeuristics flags = guessAuthorName >>=
+  maybe (getEmail flags $ return "") (getEmail flags . return)
 
 -- | Prompt for a homepage URL for the package.
 homepageHeuristics :: Interactive m => InitFlags -> m String