Using DeepSeq for exception ordering

[Nicolas Frisby]

And the important observation is: all of them throw A if interpreted in
ghci or compiled without -O, right?


On Thu, Nov 8, 2012 at 11:24 AM, Albert Y. C. Lai <trebla at vex.net> wrote:

> On 12-11-08 07:12 AM, Simon Hengel wrote:
>
>> I was just going to say that I can give at least one counterexample
>> where this does not hold:
>>
>>    evaluate (('a' : undefined) `deepseq` return () :: IO ())
>>    throwIO exceptionB
>>
>> But then I realized that here exceptionA is optimized away altogether.
>> For me this smells like a bug.  Is this related to [1]?
>>
>> [1] http://hackage.haskell.org/**trac/ghc/ticket/2273<http://hackage.haskell.org/trac/ghc/ticket/2273>
>>
>
> Interesting. A few more tests (all GHC 7.4.2, linux, x86 32-bit, use "ghc
> -O" to compile):
>
> The following cases throw A:
>
> import Control.DeepSeq
> import Control.Exception
>
> main = do
>   evaluate (('a' : error "A") `deepseq` return () :: Maybe ())
>   throwIO (userError "B")
>
> main = do
>   evaluate (('a' : error "A") `deepseq` ())
>   throwIO (userError "B")
>
> main = do
>   evaluate (('a' : error "A") `deepseq` True)
>   throwIO (userError "B")
>
> main = do
>   x <- evaluate (('a' : error "A") `deepseq` putStrLn "hi")
>   x
>   throwIO (userError "B")
>
> The following cases throw B:
>
> main = do
>   evaluate (('a' : error "A") `deepseq` return () :: IO ())
>   throwIO (userError "B")
>
> main = do
>   evaluate (('a' : error "A") `deepseq` putStrLn "hi")
>   throwIO (userError "B")
>
> main = do
>   evaluate (('a' : error "A") `deepseq` getLine)
>   throwIO (userError "B")
>
>
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