Warning suggestion: argument not necessarily a binary operator
As an example:
let fn (+) = 1; fn x = 2 in fn 1
The suggested warning is that: if an argument to a function consists entirely of characters which are symbols (all isSymbol), and the type of that argument isn't (a -> b -> c), then produce a warning.
Suggested wording is something along the lines of "Warning: the argument '(+)' isn't necessarily a binary operator, although it looks like one. This may be confusing to readers of your code."