@iamaboringperson
Surely there is some way around this problem?
As usual ARexx itself is ok, but your code is not. ARexx is very frustrating in this respect, it's so flexible it lets thru almost anything without error messages. :-)
Specifically:
PARSE VAR BLAH WITH num1'.'num2'.'num3
...is wrong. With that code the first value is assigned to variable called 'WITH'.
Either remove WITH or use:
PARSE VALUE BLAH WITH num1'.'num2'.'num3