Robert Haas <rhaas@postgresql.org> writes:
> Add notion of a "transform function" that can simplify function calls.
Why exactly was this thought to be a good idea:
> * A NULL original expression disables use of transform functions while
> * retaining all other behaviors.
AFAICT that buys nothing except to greatly complicate the API
specification for simplify_function, something that is now proving
problematic for Marti's requested refactoring [1]. If it's
inappropriate for a transform function to modify a CoerceViaIO call,
surely the transform function can be expected to know that.
regards, tom lane
[1] http://archives.postgresql.org/pgsql-hackers/2012-03/msg00694.php