Re: [Haskell-cafe] Why can `env` be assigned value two times ?

thanks for all your answers ! zaxis wrote:

defineVar :: Env -> (Id, Val) -> IOThrowsError Val defineVar envRef (id, val) = do { env <- liftIO $ readIORef envRef; env <- return $ filter (\(_id, _) -> _id/=id) env; -- clear the current scope valRef <- liftIO $ newIORef val; liftIO $ writeIORef envRef $ ((id, valRef):env); return val; }

In haskell, the variable canot change its value , right? If so, why can the `env` be assigned value twice?

Sincerely!

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