The APL language has this system variable ⎕IO (called QUAD IO -- index origin), which could be set to 0 (for 0-based indexing) or 1 globally in the environment.

The APL language has this system variable ⎕IO (called QUAD IO -- index origin), which could be set to 0 (for 0-based indexing) or 1 globally in the environment. Also, ⎕IO can be set as a local variable of a function to limit the scope of the indexing origin, which made it convenient to simplify the code to implement certain algorithms.