Synnefo » snf-ganeti

                  , specialNumericalField

-- | Wrapper around a special parse function, suitable as field-parsing

-- function.

numericalReadFn :: JSON.JSON a => (String -> JSON.Result a)

                   -> [(String, JSON.JSValue)] -> JSON.JSValue -> JSON.Result a

numericalReadFn _ _ v@(JSON.JSRational _ _) = JSON.readJSON v

numericalReadFn f _ (JSON.JSString x) = f $ JSON.fromJSString x

numericalReadFn _ _ _ = JSON.Error "A numerical field has to be a number or\ 

                                   \ a string."

-- | Wrapper to lift a read function to optional values

makeReadOptional :: ([(String, JSON.JSValue)] -> JSON.JSValue -> JSON.Result a)

                    -> [(String, JSON.JSValue)]

                    -> Maybe JSON.JSValue -> JSON.Result (Maybe a)

makeReadOptional _ _ Nothing = JSON.Ok Nothing

makeReadOptional f o (Just x) = fmap Just $ f o x

-- | Sets the read function to also accept string parsable by the given

-- function.

specialNumericalField :: Name -> Field -> Field

specialNumericalField f field =

  if (fieldIsOptional field == NotOptional)

     then field { fieldRead = Just (appE (varE 'numericalReadFn) (varE f)) }

     else field { fieldRead = Just (appE (varE 'makeReadOptional)

                                         (appE (varE 'numericalReadFn)

                                               (varE f))) }