wta: Allow --different-values for powerset

Even if it only allows a range of [1,2], it's there for completeness and makes
the benchmark script a bit easier.

src/random-wta/Generator.hs

@@ -30,7 +30,9 @@ runGenerator config action = runReaderT action config
 genMonoidValue :: Generator m m
 genMonoidValue = asks ((monoid . spec) &&& differentValues) >>= \case
   (Powerset, Nothing) -> liftIO $ randomIO
-  (Powerset, _) -> error $ "differentValues not supported for powerset" -- FIXME detect this early (and handle the case <=2)
+  (Powerset, Just 1) -> return True
+  (Powerset, Just 2) -> liftIO $ randomIO
+  (Powerset, _) -> error $ "differentValues >2 not supported for powerset"
   (OrWord, Nothing)   -> liftIO $ randomIO
   (OrWord, Just x)   -> liftIO $ randomRIO (1, fromIntegral x)
   (MaxInt, Nothing)   -> liftIO $ randomIO

src/random-wta/Main.hs

@@ -17,6 +17,8 @@ import qualified Text.Megaparsec.Char.Lexer    as Mega
 import           Data.Void
 import           System.Random
 import           Numeric
+import           System.IO
+import           System.Exit
 
 import           Types
 import           Generator
@@ -115,6 +117,13 @@ main = do
         Options.info (parseOpts Options.<**> Options.helper) (Options.fullDesc)
   opts <- Options.execParser optSpec
 
+  case optMonoid opts of
+    SomeMonoid Powerset
+      | maybe False (>2) (optDifferentValues opts) -> do
+          hPutStrLn stderr "error: Powerset can't have more than 2 different values"
+          exitFailure
+    _ -> return ()
+
   case optRandomState opts of
     Nothing -> return ()
     Just x  -> setStdGen x

src/random-wta/Types.hs

@@ -19,7 +19,6 @@ data MonoidType m where
   OrWord ::MonoidType Word
   Powerset ::MonoidType Bool
 
-
 -- | For each arity, the number of symbols
 type SymbolSpec = Vector Int