(require mzlib/unit)

The mzlib/unit library mostly re-provides scheme/unit, except for struct from scheme/unit.

(struct id (field-id ...) omit-decl ...)

omit-decl   =   -type     |   -selectors     |   -setters     |   -constructor

A signature form like struct from scheme/unit, but with a different syntax for the options that limit exports.