On Fri, Jan 28, 2011 at 8:39 AM, Henning Thielemann
Evan Laforge schrieb:
One of the first things I did when starting a larger haskell project was to write a preprocessor that would replace certain tokens with (token_srcpos (filename, func_name, lineno)) and then write x and x_srcpos versions of the various 'throw' and logging functions. This is extremely handy to have, and since logs are part of my app's UI, it's part of the app itself.
I suspect that if you add source position information to 'throw' then you use 'throw' for showing (unintended) programming errors, but 'throw' is not intended for this purpose, but for expected problems like 'file not found' and so on. Adding source position to 'error', 'undefined', irrefutable patterns and logging functions for debugging makes sense to me, but for 'throw'?
When I say 'throw' I mean ErrorT.throwError, which boils down to returning Left or Nothing. I.e. expected errors, used simply for early return. And especially in the case of Nothing, when debugging it's important to know which particular guard failed to make the operation "expectedly" unexpectedly abort. Otherwise I wind up sticking 'trace's in strategic points to see where execution is going, which is just a pain. For the IO 'throw' srcpos info is just as important even if it's a program crashing error, so I guess I disagree no matter which 'throw' we're talking about.