On Mon, 21 Apr 2008, Donn Cave wrote:
On Apr 21, 2008, at 11:18 AM, John Goerzen wrote:
In the case of using "error", we can happily process the data assuming everything will be fine, and raise an error if and when it is encountered. By using Either, however, any pattern match on the Left/Right result is going to force the entire input to be evaluated so that we can know whether or not it had any error.
Is this analysis sensible? If so, are there better solutions?
In another thread back on March 12 ("Exception handling when using STUARrray") I read `Since the decision between Left and Right requires all parts to be evaluated, it's Either that might too strict for your application. What about a writer monad, where exceptions, or better say warnings, are written to the writer stream?'
I don't believe I ever got around to evaluating that recommendation (lazy evaluation strategy, indeed.) I think I would use "error".
Was this advise from me? I would advise the Writer monad again. 'error' should be used only for programming errors, not for unexpected data or situations from the outside world. http://www.haskell.org/haskellwiki/Exception http://www.haskell.org/haskellwiki/Error