RESO Rules: Empty values and COALESCE

[bryanburgers]

I’ve been reading through the RESO Validation Expression spec’s List of Functions and List of Operators and I can’t tell what should happen when an empty field is used in an operation.

Take, for example, the expression 7 + .EMPTY.. Loosely typed programming languages tend to take either a very lax stance to something like this by automatically coercing values that don’t match (e.g. 7 + null is 7 in JavaScript) or a strict stance (e.g. 7 + None is an error in Python). I can’t tell from the spec which camp RESO Validation Expression language falls into.¹

Are there any existing implementations that depend on one or the other interpretation?

If not, I propose that the expression language take a strict stance, and treat operations between unlike values, like 7 + .EMPTY. as an error.

I further propose we introduce a new function, COALESCE², to explicitly handle what to do with empty values. This function would take any number of arguments, and return the first non-empty value.

Right now, I have a lot of rules that use an IIF to do coalescing. They look roughly like

IIF(GarageSpaces != .EMPTY., GarageSpaces, 0) + IIF(OpenParkingSpaces != .EMPTY., OpenParkingSpaces, 0)

With COALESCE, this would look more like

COALESCE(GarageSpaces, 0) + COALESCE(OpenParkingSpaces, 0)

Footnotes

1. The spec does define what happens when adding floats and integers; those two are like-enough that that makes sense. Python, used as an example of taking a strict stance, also allows adding floats and integers. ↩

2. Name taken from Microsoft SQL Server; I'm open to other options. ↩