[Haskell-cafe] Re: A GHC error message puzzle

[Wei Hu]

Anyone care to explain why? I also tested a slightly changed program
pasted below, and am very confused.

> main = do
>   -- This call doesn't terminate, why?
>   print $ nonTermination "a"
>   -- Comment the above line to test the rest of the code
>   -- RTS detects the loop and bails out
>   print $ process "abc"
>   -- Comment the above line to test the rest of the code
>   inp <- readFile "input"
>   -- I'm guessing (process inp) throws an exception,
>   -- and the handler closes all files, making a second close fail?
>   writeFile "output" $ process inp

> process :: String ->  String
> process xs = blackhole where blackhole = tail blackhole

> nonTermination :: String -> String
> nonTermination _ = blackhole where blackhole = blackhole


On Thu, Aug 12, 2010 at 3:38 PM, Simon Marlow <marlowsd at gmail.com> wrote:
> On 12/08/10 15:09, Yitzchak Gale wrote:
>>
>> The file "error_puzzle.hs" begins like this:
>>
>> main = do
>>   inp<- readFile "input"
>>   writeFile "output" $ process inp
>>
>> process :: String ->  String
>>
>> When compiled with GHC 6.12.3 and run, it
>> gives the following result:
>>
>> $ ./error_puzzle
>> error_puzzle: output: hClose: illegal operation (handle is finalized)
>
> process xs = blackhole where blackhole = tail blackhole
>
> Cheers,
>        Simon
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