ESL supports external subroutines and functions, which run on systems that support use of dynamic link libraries (DLLs).

 

External subroutines and external functions are written in a language other than ESL and are compiled into a Windows DLL. Before either an external subroutine or function can be used in an action statement, it must be declared so that ESL knows what argument types it needs and what library it is in.

 

For example:

 

subroutine MIN (float: ArrayIn, float: Minimum)

    library "mathlib"

 

function WeekDay (integer:Year, integer:Month,

    integer:Day) returns string

    library "datelib"

 

Libraries provided with ESL have include files that contain declarations for all the subroutines and functions in the library.