The system variable ŒCS (Compatibility Setting) can be used to ensure that applications written under APL.68000 Level I work in the same way under APLX. It can be set to a number in the range 0 to 7. It is normally set to 0, but if a Level I workspace is loaded it will automatically be set to 7. The behaviour affected by ŒCS is as follows:
ŒCS„1 Expressions of the form 5 6 7[2] will be allowed rather than giving RANK ERROR.
ŒCS„2 ŒNC and ŒNL will use the code 4 rather than ¯1 to indicate an invalid name.
ŒCS„4 Default formatting of numeric arrays uses the same width for all columns, rather than determining the width separately for each column.
The three parameters can be set in any combination by adding together the codes. For example:
ŒCS„0 1 3 5[2] RANK ERROR 1 3 5[2] ^ 2 3½1 2 3 1 100 1000 (Each column has its own format) 1 2 3 1 100 1000 ŒCS„5 (Set codes 1 and 4) 1 3 5[2] 3 2 3½1 2 3 1 100 1000 (All columns share the same format) 1 2 3 1 100 1000