Added functions and types for generating config file

Data/Configurator.hs

@@ -55,6 +55,16 @@ module Data.Configurator
     , subconfig
     , addToConfig
     , addGroupsToConfig
+    -- * Generating a new configuration file
+    -- $output
+    , emptyConfigFile
+    , addConfigFileComment
+    , addConfigFileNewline
+    , addConfigFileImport
+    , addConfigFileBind
+    , addConfigFileGroup
+    , configFileText
+    , writeConfigFile
     -- * Helper functions
     , display
     , getMap
@@ -85,6 +95,7 @@ import qualified Data.Attoparsec.Text as T
 import qualified Data.Attoparsec.Text.Lazy as L
 import qualified Data.HashMap.Lazy as H
 import qualified Data.Text as T
+import qualified Data.Text.IO as T
 import qualified Data.Text.Lazy as L
 import qualified Data.Text.Lazy.IO as L
 
@@ -385,6 +396,59 @@ empty = Config "" $ unsafePerformIO $ do
                      , cfgMap = m
                      , cfgSubs = s
                      }
+
+-- | An empty 'ConfigFile'.
+emptyConfigFile :: ConfigFile
+emptyConfigFile = []
+
+-- | Appends a comment to the 'ConfigFile'.
+addConfigFileComment :: T.Text -> ConfigFile -> ConfigFile
+addConfigFileComment t f = f ++ [FComment t]
+
+-- | Appends a newline to the 'ConfigFile'.
+addConfigFileNewline :: ConfigFile -> ConfigFile
+addConfigFileNewline f = f ++ [FNewline]
+
+-- | Appends an import directive to the 'ConfigFile'.
+addConfigFileImport :: Path -> ConfigFile -> ConfigFile
+addConfigFileImport p f = f ++ [FImport p]
+
+-- | Appends a bind directive to the 'ConfigFile'.
+addConfigFileBind :: Name -> T.Text -> ConfigFile -> ConfigFile
+addConfigFileBind n v f = f ++ [FBind n v]
+
+-- | Appends the first 'ConfigFile' as a named group in the second 'ConfigFile'.
+addConfigFileGroup :: Name -> ConfigFile -> ConfigFile -> ConfigFile
+addConfigFileGroup n sub f = f ++ [FGroup n sub]
+
+-- TODO: Might want to add more value to addConfigFileBind function by
+-- searching for and replacing duplicate bind directives within the
+-- same group.
+
+
+(##) :: T.Text -> T.Text -> T.Text
+(##) = T.append
+
+-- hws is shorthand for horizontal white space
+fileEntryAsText :: T.Text -> FileEntry -> T.Text
+fileEntryAsText hws (FComment c) = hws ## "# " ## c ## "\n"
+fileEntryAsText _hws (FNewline) = "\n"
+fileEntryAsText hws (FImport p)  = hws ## "import \"" ## p ## "\"\n"
+fileEntryAsText hws (FBind n v)  = hws ## n ## " = " ## v ## "\n"
+fileEntryAsText hws (FGroup n f) =
+    hws ## n ## " {\n" ##
+        foldl (\acc new -> (##) acc $ fileEntryAsText (hws ## "  ") new) T.empty f ##
+        hws ## "}\n"
+
+-- | Converts a 'ConfigFile' type to formatted text.
+configFileText :: ConfigFile -> T.Text
+configFileText [] = T.empty
+configFileText conf = foldl (\acc new -> (##) acc $ fileEntryAsText "" new) T.empty conf
+
+-- | Writes a 'ConfigFile' as a formatted text file at the given 'FilePath'.
+writeConfigFile :: FilePath -> ConfigFile -> IO ()
+writeConfigFile path conf = T.writeFile path $ configFileText conf
+
 {-# NOINLINE empty #-}
 
 -- $format
@@ -524,3 +588,12 @@ empty = Config "" $ unsafePerformIO $ do
 -- reconfigure, a subsystem may ask to be notified when a
 -- configuration property is changed as a result of a reload, using
 -- the 'subscribe' action.
+
+-- $output
+--
+-- Configuration files can be generated algorithmically and written in
+-- the correct format.  A 'ConfigFile' is a list of 'FileEntry'
+-- members, and as such can be manipulated using standard list
+-- functions.  Alternatively, the builder functions 'addConfigFileComment',
+-- 'addConfigFileBind', etc. may be used.
+--

Data/Configurator/Types.hs

@@ -22,6 +22,9 @@ module Data.Configurator.Types
     -- * Notification of configuration changes
     , Pattern
     , ChangeHandler
+    -- * Types for generating config files
+    , FileEntry(..)
+    , ConfigFile
     ) where
 
 import Data.Configurator.Types.Internal

Data/Configurator/Types/Internal.hs

@@ -29,6 +29,8 @@ module Data.Configurator.Types.Internal
     , exact
     , prefix
     , ChangeHandler
+    , FileEntry(..)
+    , ConfigFile
     ) where
 
 import Control.Exception
@@ -214,3 +216,14 @@ data Value = Bool Bool
 data Interpolate = Literal Text
                  | Interpolate Text
                    deriving (Eq, Show)
+
+-- | Single entry of a desired configuration to be written to file.
+data FileEntry = FComment Text
+               | FNewline
+               | FImport Path
+               | FBind Name Text
+               | FGroup Name ConfigFile -- arbitrary grouping
+               deriving (Eq)
+
+-- | Representation of a configuration file for writing to disk.
+type ConfigFile = [FileEntry]

tests/Test.hs

@@ -30,7 +30,8 @@ tests = TestList [
     "types"  ~: typesTest,
     "interp" ~: interpTest,
     "import" ~: importTest,
-    "reload" ~: reloadTest
+    "reload" ~: reloadTest,
+    "write"  ~: writeTest
     ]
 
 withLoad :: [Worth FilePath] -> (Config -> IO ()) -> IO ()
@@ -166,3 +167,36 @@ reloadTest = withReload [Required "resources/pathological.cfg"] $ \[Just f] cfg
     r2 <- takeMVarTimeout 2000 wongly
     assertEqual "notify not happened" r2 Nothing
 
+testConfig :: ConfigFile
+testConfig =
+    [ FComment "This is a test comment"
+    , FComment "And here is a new one"
+    , FNewline
+    , FImport "pathological.cfg"
+    , FBind "myBindVar" "\"here's my bind string\""
+    , FBind "myInt" "32 # This is a trailing comment as part of a bind"
+    , FComment "Ok, let's try a group now"
+    , FGroup "group1"
+        [ FComment "Starting group 1"
+        , FBind "group1a" "7"
+        , FBind "group1b" "90"
+        , FGroup "group2"
+            [ FComment "I am nested!"
+            , FImport "import.cfg"
+            , FBind "group2a" "\"nested var\""
+            ]
+        , FComment "End the group"
+        ]
+    , FNewline
+    , FComment "A couple more binds for good measure"
+    , FBind "penultimate" "\"almost\""
+    , FBind "final" "\"there\""
+    ]
+
+
+writeTest :: Assertion
+writeTest = do
+    writeConfigFile "resources/testoutput.cfg" testConfig
+    withLoad [Required "resources/testoutput.cfg"] $ \_cfg -> do
+        assertBool "Failed to load write test file if here" True
+

tests/configurator-tests.cabal

@@ -10,7 +10,7 @@ Executable configurator-test
                      directory,
                      HUnit,
                      text,
-                     attoparsec-text,
+                     attoparsec,
                      unordered-containers,
                      unix-compat,
                      hashable,