8 ways to report errors in Haskell
Posted by Eric Kidd Sun, 11 Mar 2007 00:05:00 GMT
Haskell is a marvellous language, but there are some things I don’t like about it. My least favorite: Haskell has no fewer than 8 different APIs for reporting errors.
To make a bad situation worse, the choice of API varies between popular libraries. To give a particularly unfortunate example, Network.URI.parseURI and Network.HTTP.simpleHTTP report errors in entirely different ways, turning a “download this URL” program into a page of code, nearly half of which is devoted to dealing with various kinds of errors. (The rest is boilerplate that could be refactored into a nice wrapper.)
Let’s begin with a toy function, the simplest possible program that could actually fail:
myDiv x y = x / y
As every algebra student knows, we can’t divide by zero. Using this function as our example, let’s take a look at all the different ways we can implement error-reporting in Haskell.
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