$DATA $INPUT $EST - user-defined settings

[joaoabr]

Maybe $DATA, $INPUT, and $EST will be developed further in the future but would it be possible for the time being to allow the user to specify expressions manually? For instance, if one would like to have MAXEVAL=0 in $EST, this could be achieved by specifying something like + additional_est_spec("MAXEVAL=0") . An identical mechanism could be used to specify the dataset name in $DATA, or items in $INPUT, which would be useful if the user would like to use this package as a standalone tool. This is just a suggestion for your consideration.