write the json representation of value v into the file file. Only bool, string, numeric, map, tab and their nestings can be translated into Json, cf. sect. Defining a value in Json format

See also Data Exchange Functions: @dump,    @dumpvar,    @gnuplot,    @json_read,    @json_string,    @json_write,    @loadvalue,    @loadvar,    @nim2vezer    @parse,    @plot,    @read_file,    @rplot,    @savevalue,    @set_osc_handling_double,    @set_osc_handling_int64,    @set_osc_handling_tab,    @string2fun,    @string2obj,    @string2proc    @to_num    @xml_read    @xml_string