Eric Seidel <e...@seidel.io> writes: > Hi Richard, > > Sorry for all of the confusion, it seems the docs do indeed need some > love! > > On Sun, Dec 6, 2015, at 20:56, Richard Eisenberg wrote: >> That looks like exactly what I want. Thanks. >> >> There remain two mysteries: >> - I thought that CallStacks were a new feature that would come with GHC >> 8.0. Yet it seems the datatype is present in base-4.8.x. Even though the >> docs even say (wrongly, evidently) that it's in base since 4.9. > > They were originally merged into 7.11, but were backported to the > official 7.10.2 release due to popular demand. It appears the @since > annotation wasn't updated correspondingly. > >> - That function seems missing in HEAD. Or maybe it moved. A little >> searching says it *did* move, to GHC.Exception. > > In HEAD we are now using CallStacks for error and undefined, which was > not the case for the 7.10.2 release. This means the type needs to be > defined much earlier in base, before we even have enough functionality > to write a sensible formatter. showCallStack currently lives in > GHC.Exception because that's where it's used, but that's not a good > reason... I'll take another look at moving it back to GHC.Stack.
Indeed, this is probably a more logical place for them to live. Recent experience tells me that there is a great potential for import cycles in this area, however. I wish you luck ;) >> Well, my problem is solved. But I think the documentation needs a pass >> here. And is there a reason not to have a Show instance? > > I usually only use compiler-derived Show instances so that Read > automatically works, as well as some nice formatting libraries like > http://hackage.haskell.org/package/pretty-show for debugging. For > pretty-printing like showCallStack I prefer a standalone function or a > separate type-class. Sure, I don't see any harm in deriving a Show instances, however. You may want to derive it with standalone deriving so you can then attach a Haddock pointing to the pretty version. e.g., data CallStack = ... -- | See also 'prettyCallStack'. deriving instance Show CallStack > If the name "showCallStack" suggests the compiler-derived output, we > could change it to something like "prettyCallStack" or > "formatCallStack", I don't have a strong opinion there. I have also struggled with these sorts of naming decisions. The overloading of the word "show" is a bit problematic. (+1) for "pretty". Cheers, - Ben
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