[Haskell] Re: Exceptions

[John Goerzen]

On 2004-11-23, Johannes Waldmann [EMAIL PROTECTED] wrote:
 in the following example, the handler won't catch the exception
 because of lazy evaluation. therefore, it's a different story
 than with exceptions in ML, Python, whatever strict language.

 main = do
  xs - return [ 1, 2, error throw ]
  `catch` \ any - do
  putStrLn caught
   return [ 4, 5, 6 ]
  print xs

That didn't quite compile as-is; I assume you ment:

main = do
 xs - return [ 1, 2, error throw ]
 `catch` \ any - do
 putStrLn caught
 return [ 4, 5, 6 ]
 print xs

When run, I get: Fail: throw

In any case, in the more general case, I don't see a problem with that.
I get an exception when I try to use something.  That's fine.  In an
imperative program that solves the same problem the same way, you'd see
the exception at the same point.


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Re: [Haskell] Re: Exceptions

[Ben Rudiak-Gould]

John Goerzen wrote:
main = do
 xs - return [ 1, 2, error throw ]
 `catch` \ any - do
 putStrLn caught
 return [ 4, 5, 6 ]
 print xs

When run, I get: Fail: throw

In any case, in the more general case, I don't see a problem with that.
I get an exception when I try to use something.  That's fine.  In an
imperative program that solves the same problem the same way, you'd see
the exception at the same point.
No, in a traditional (strict) programming language the program would print
   caught
   [4,5,6]
The exception throw would not appear in the output.
-- Ben
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