I am struggling to understand why I am unable to create certain compound data types in my IDL programs. I came upon this problem in my code while trying to use the data types LIST and HASH and after further inspection I found that I also cannot produce DICTIONARY and ORDEREDHASH.

For example, following the syntax given on the page -

https://www.harrisgeospatial.com/docs/IDL_Data_Types.html

I get the following result when trying to construct a hash data type

IDL> h = HASH('Id',1234)
% Variable is undefined: HASH.
% Execution halted at: $MAIN$

and similarly

IDL> l = LIST(1,2)
% Variable is undefined: LIST.
% Execution halted at: $MAIN$

I have IDL version 8.5.1 and I am running on Mac OS X El Capitan Version 10.11.6