hist_field_name
field_name = hist_field_name(field->operands[0], ++level);
strcat(expr, hist_field_name(field, 0));
test_name = hist_field_name(hist_field, 0);
field_name = hist_field_name(key_field, 0);
field_name = hist_field_name(hist_data->fields[i], 0);
const char *field_name = hist_field_name(hist_field, 0);