# Consumes an iterator of expressions and tries to map each element to
	# its corresponding Instance.
	#
	# If any AExprs doesn't resolve to an Instance, then it returns null.
	# Otherwise return an array of instances
	fun aexprs_to_instances(aexprs: Iterator[AExpr]): nullable Array[Instance]
	do
		var accumulator = new Array[Instance]
		for aexpr in aexprs do
			var instance = expr(aexpr)
			if instance == null then return null
			accumulator.push(instance)
		end
		return accumulator
	end