nub out repeated vars

Author: dorchard

frontend/granule-frontend.cabal

@@ -1,6 +1,6 @@
 cabal-version: 1.12
 
--- This file has been generated from package.yaml by hpack version 0.37.0.
+-- This file has been generated from package.yaml by hpack version 0.38.1.
 --
 -- see: https://github.com/sol/hpack
 
@@ -128,6 +128,7 @@ test-suite frontend-spec
   other-modules:
       Data.Bifunctor.FoldableSpec
       Language.Granule.Checker.CheckerSpec
+      Language.Granule.Checker.KindSpec
       Language.Granule.Checker.MonadSpec
       Language.Granule.Checker.SubstitutionsSpec
       Language.Granule.Checker.TypesSpec

frontend/src/Language/Granule/Checker/Kinding.hs

@@ -17,7 +17,7 @@ import Control.Monad.State.Strict
 import Control.Monad.Trans.Maybe
 import Data.Functor.Identity (runIdentity)
 import Data.Maybe (fromMaybe)
-import Data.List (isPrefixOf, sortBy, (\\))
+import Data.List (isPrefixOf, sortBy, (\\), nub)
 
 import Language.Granule.Context
 
@@ -1382,7 +1382,9 @@ instance Unifiable t => Unifiable (Maybe t) where
 -- the given kind
 typeVarsOfKind :: (?globals :: Globals) => Type -> Kind -> Checker [Id]
 typeVarsOfKind t k = do
-  typeFoldM algebra t where
+    vars <- typeFoldM algebra t 
+    return (nub vars)
+  where
     algebra = TypeFold
       { tfTy = \_ -> return []
       , tfFunTy = \_ _ x y -> return (x ++ y)