Write new Format and Formats types, some helper functions

pandoc-types.cabal

@@ -47,6 +47,7 @@ Library
                      Text.Pandoc.Builder
                      Text.Pandoc.JSON
                      Text.Pandoc.Arbitrary
+                     Text.Pandoc.Format
   Other-modules:     Paths_pandoc_types
   Autogen-modules:   Paths_pandoc_types
   Build-depends:     base >= 4.5 && < 5,

src/Text/Pandoc/Arbitrary.hs

@@ -6,10 +6,12 @@ where
 import Test.QuickCheck
 import Control.Applicative (Applicative ((<*>), pure), (<$>))
 import Control.Monad (forM)
+import qualified Data.Set as Set
 import Data.Text (Text)
 import qualified Data.Text as T
 import Text.Pandoc.Definition
 import Text.Pandoc.Builder
+import qualified Text.Pandoc.Format as F
 
 realString :: Gen Text
 realString = fmap T.pack $ resize 8 $ listOf $ frequency [ (9, elements [' '..'\127'])
@@ -398,3 +400,17 @@ instance Arbitrary ListNumberDelim where
                    2 -> return OneParen
                    3 -> return TwoParens
                    _ -> error "FATAL ERROR: Arbitrary instance, logic bug"
+
+instance Arbitrary F.KnownFormat where
+        arbitrary = arbitraryBoundedEnum
+
+instance Arbitrary F.Format where
+        arbitrary = frequency $ [(80, F.KnownFormat <$> arbitrary)
+                                ,(20, F.CustomFormat . T.pack <$> arbitrary)]
+        shrink F.KnownFormat{}    = []
+        shrink (F.CustomFormat t) = F.CustomFormat <$> shrinkText t
+
+instance Arbitrary F.Formats where
+        arbitrary = F.exactly <$> arbitrary
+        shrink (F.OneOfFormats s) = F.exactly <$> shrink (Set.toList s)
+        shrink (F.NoneOfFormats s) = F.exactlyNone <$> shrink (Set.toList s)