Err package:what4

This datatype describes how a solver will behave following an error.
Something bad
Reject the new option value with an error message.
Get return type of solver fn.
Either a partial value, or a straight-up error.
This indicates the solver will remain live and respond to further commmands following an error
Indicate this solver's behavior following an error response
The solver's stdout, for easier parsing of responses.
Standard error for the solver process
Query the solver's error behavior setting