In order to call an external subroutine or function that is contained in a DLL from an ESL program, the subroutine or function must first be declared.

ESL distinguishes between routines as follows:

•Functions pass parameters by value or reference and return a result back to the caller.

•Subroutines pass all of their parameters by reference. These routines can have integer, floating point, boolean, string, arrays, and structure arguments.

•Functions will return integer, floating point, boolean, or string values.

•Subroutines do not return a value, but set the value of the in-built function “errorlevel”.