I've been wanting to get warnings on partial functions (and partial record accessors, while we're at it!) for some time.
And, I think it would be quite easy to have GHC infer partiality. As far as I can see, partiality can come from only two places: the use of a partial function, and an incomplete pattern match. (I'm ignoring nontermination here, which I think is best considered separately.) Before getting this into GHC, though, we'd need to make sure the incomplete-pattern-match checker is up for it (see #3927), but that work is being done right now. And we'd definitely need a way for users to declare "This function is total! Really!"
I like the idea of user-specified warning categories, but I think partiality is easy enough for GHC to infer that it should be built in.
+1 on partiality warnings, preferably inferred
+0.8 on user-specified warning classes (but inferred partiality is my preference)
-0.9 on just attaching a one-off warning to fromJust (we can do so much better)
-1 on removing fromJust (I use it myself [don't hate me for it], and the GHC codebase uses `expectJust`, which takes a string for better error messages, 54 times by my count)
Richard
On Feb 24, 2015, at 7:28 AM, Herbert Valerio Riedel
On 2015-02-24 at 12:32:14 +0100, Michael Snoyman wrote:
We could also automatically detect basic partiality, like incomplete pattern matches, and add partiality warnings. Depending on how much work that is, it may be easier than trying to mark up all of base correctly.
You'd still need a way to greenlight false positives. I.e. cases where the code *seems* to have unhandled pattern matches which can't happen, but which GHC can't prove them not to be unhandled... _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries