An intrinsic function is actually a call to a subroutine that acts like a data item. You can’t use an intrinsic function as the destination of a MOVE or in any command that attempts to use it as a destination type data item.
An intrinsic function acts like a constant or a read-only value
The following statements are illegal because the intrinsic function is being used as the destination of a MOVE or STRING:
MOVE “199701011236174800000” TO FUNCTION CURRENT-DATE.
STRING “199701011236174800000” DELIMITED BY SIZE
INTO FUNCTION CURRENT-DATE.
An intrinsic function doesn’t actually modify the data item arguments that it operates on. Instead, it creates a temporary variable and acts on that.
In the following example, after the two statements are executed, ALPHA-FIELD still contains the lowercase “hello”, while OTHER-FIELD now contains “HELLO”.
The call to FUNCTION UPPER-CASE(ALPHA-FIELD) doesn’t modify the contents of ALPHA-FIELD:
MOVE "hello" TO ALPHA-FIELD. MOVE FUNCTION UPPER-CASE(ALPHA-FIELD) TO OTHER-FIELD.