It's funny for me to see all these references to 'IDL' describing "Interactive Data Language". I had only associated the term IDL with 'Interface Definition Language' [1].
[1] https://en.wikipedia.org/wiki/Interface_description_language
[1] https://en.wikipedia.org/wiki/Interface_description_language
It's a popular (and frankly terrible) language used in astronomy and astrophysics. My first (semi-professional) programming job was a high school internship at NASA AMES writing IDL to process data from the Cassini probe orbiting Saturn. At that time you had to use a clunky IDE for development and the whole toolchain was proprietary.