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lib/Infer/Treat.hs

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+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE NamedFieldPuns #-}
+module Infer.Treat where
+
+import Data.Aeson (ToJSON, FromJSON, eitherDecode)
+import Data.ByteString.Lazy.UTF8 (fromString)
+import GHC.Generics (Generic)
+import qualified Data.Set as S
+
+data Rule = Rule {
+  premises :: S.Set String,
+  conclusion :: String
+}
+  deriving (Eq, Ord, Show, Generic)
+
+instance ToJSON Rule
+instance FromJSON Rule
+
+run :: String -> [String] -> Either String [String]
+run input pre = fmap f (eitherDecode $ fromString input)
+  where f = S.toList . infer (S.fromList pre)
+
+infer :: S.Set String -> [Rule] -> S.Set String
+infer pre env =
+  let (found, nenv) = find
+  in if S.isSubsetOf found pre
+     then pre
+     else infer (S.union found pre) nenv
+  where find = foldr mlook (S.empty, []) env
+        mlook r@Rule{premises, conclusion} (f, e) =
+          if S.isSubsetOf premises pre
+          then (S.insert conclusion f, e)
+          else (f, r:e)