What are the changes to this file vs. the ExprTyper that (I assume) this was copy/pasted from?

Seems like there should be a few "// NOTE: Changed for Spark because of X or Y" comments in here that explain to future maintainers how this is exactly different from Scala's ExprTyper, and why.

Right now the only line that looks remotely related to Spark (as in it mentions a Spark type) is the "repl: SparkIMain"...was that really the only change? I have no idea...just can't tell without looking at the Scala source what has changed.