1 files changed, 40 insertions, 0 deletions

diff --git a/Unique.hs b/Unique.hs
new file mode 100644
index 0000000..13ae7cf
--- /dev/null
+++ b/Unique.hs
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+module Unique
+    ( UniqueFactory
+    , Unique
+    , uniqueSymbol
+    , substituteUnique
+    , multipleOccurances
+    ) where
+
+import Data.Generics.Aliases
+import Data.Generics.Schemes
+import Language.Haskell.Exts.Syntax
+
+newtype UniqueFactory = UniqueFactory Integer
+
+newtype Unique = Unique Integer
+ deriving (Eq,Ord)
+
+freshUniques :: UniqueFactory
+freshUniques = UniqueFactory 0
+
+genUnique :: UniqueFactory -> (Unique,UniqueFactory)
+genUnique (UniqueFactory c) = (Unique c, UniqueFactory (succ c))
+
+uniqueSymbol :: Unique -> Exp ()
+uniqueSymbol (Unique i) = Var () (UnQual () (Ident () (showSym i)))
+
+showSym :: Integer -> String
+showSym i = " u" ++ show i
+
+substituteUnique :: Unique -> Exp () -> Exp () -> Exp ()
+substituteUnique u inner outer = everywhere (mkT $ subst inner) outer
+ where
+    subst x t | t == uniqueSymbol u  = x
+              | otherwise            = t
+
+
+multipleOccurances :: Unique -> Exp () -> Bool
+multipleOccurances u x = case listify (== uniqueSymbol u) x of
+    (x:y:ys) -> True
+    _        -> False