Net.Data uses two structures to communicate with your language environment. Your language environment must work with these structures and set and pass information within the structures.
Net.Data passes a language environment interface structure (for example, dtw_lei_t) to the language environment function that it calls. The structure contains, among other things, a parameter data array that contains a list of parameters to be passed to the language environment function. The language environment function called by Net.Data processes the request, updates the parameters in the parameter data array (if applicable), and returns to Net.Data.
Net.Data then goes through the parameter data array, updates its copies of the parameters to reflect the new values set by the language environment function, and continues the processing of the Net.Data macro.