"Hal Daume III"
I'm not sure how "generally useful" this would be, but I would find it useful to be able to attach notes to core expressions from the Haskell code. The idea being something along the lines of a code annotation like a pragma. [...]
Simon Peyton-Jones
[...] There is an annotation facility in Core, but it's easy for the notes to be discarded. So if they are conveying important info, it might easily get lost... and if not, what's it doing there in the first place. What do you expect to happen to these annotations? [...]
It seems like _scc_ is (almost) exactly what you need here. When used
for profiling, you mark subexpressions you want profiled and ghc takes
care to preserve and propagate them in a semantically meaningful way.
Any _scc_ annotations that ghc chooses to drop can be reported as
bugs :-)
I say "almost" because what the semantics used when profiling may not
be the right ones for your purposes. (I'm being vague because I don't
know your purposes.)
Naturally, you'd want to be able to use these notes independently of
profiling - which can probably be done with a little preprocessor
hackery. Assuming that the 1st argument to 'NOTE' is a literal string
in the following:
#ifdef TRACK_NOTES
#define NOTE(x,y) (_scc_ "