1 files changed, 18 insertions, 0 deletions
diff --git a/src/InitOnce.hs b/src/InitOnce.hs
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index 0000000..60ea435
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+++ b/src/InitOnce.hs
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+{-# LANGUAGE TemplateHaskellQuotes #-}
+module InitOnce (once) where
+
+import Language.Haskell.TH (bindCode, CodeQ)
+import Type.Reflection (Typeable, typeOf)
+
+import InitOnce.TheMap (onceInsert)
+import InitOnce.Types (Location, location', TypedAny(..), getTypedAny)
+
+
+-- | The IO action is executed with asynchronous exceptions masked (using
+-- 'Control.Concurrent.MVar.modifyMVarMasked') to ensure that initialisation
+-- really happens once.
+once :: Typeable a => CodeQ (IO a) -> CodeQ a
+once code = bindCode location' $ \loc -> [|| typedOnceInsert loc $$(code) ||]
+
+typedOnceInsert :: Typeable a => Location -> IO a -> a
+typedOnceInsert loc act = getTypedAny (onceInsert loc ((\x -> TypedAny (typeOf x) x) <$> act))