In article <[EMAIL PROTECTED]>,
John Meacham <[EMAIL PROTECTED]> wrote:
> I am a fan of allowing top level declarations of the form:
>
> foo <- newIORef "foo"
>
> which would behave as an initializer, with the semantics being that it
> be evaluated at most once before foos first use. (so it could be
> implemented via unsafePerformIO or as an init section run before main).
>
> The
> {-# NOINLINE foo #-}
> foo = unsafePeformIO $ newIORef "foo"
>
> idiom is so common and useful, it should have some compiler support. It
> is 'clean' too, since all we are doing is extending the "world" with new
> state, but in a much cleaner/safer way then writing to a file or environment
> variable or other methods of storing state in the world.
Clean it is not:
foo :: a
foo <- newIORef undefined
writeChar :: Int -> IO ()
writeChar x = writeIORef foo x
readString :: IO String
readString = readIORef foo
cast :: Char -> IO String
cast c = (writeChar c) >> readString
--
Ashley Yakeley, Seattle WA
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