Hi all,

GHC HEAD currently suggests valid in-scope single-identifier substitutions for 
typed holes (underscores in terms). Some unrelated work somehow changed the 
output, and I'm wondering if this is a change for the better or for the worse.

The test case is this:

> f :: Int -> Int -> Int
> f x y = _ x y

With my patch, GHC now suggests `pure` and `return` as replacements for _ 
(along with the other top contenders of (-), asTypeOf, and const). (You can 
also increase the number of suggestions, which will then include (+) and (*) 
among others.) It's true that `pure` and `return` fit the bill, noting that 
((->) Int) is an Applicative. But I doubt these suggestions will help the user.

I'm not keen to make fixing this "valid suggestions" feature (which I do really 
like) a dependency of finishing my patch, but I also don't want the change to 
output to go unnoticed. So, I'm asking: when I merge my patch, should I post a 
bug asking for perhaps a priority ordering of suggestions?

Thanks,
Richard
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