Trust, but Verify
When you write functions that operate on S3 or unclassed objects you can either trust that your inputs will be structured as expected, or tediously check that they are.
vetr takes the tedium out of structure verification so that you can trust,
but verify. It lets you express structural requirements declaratively with
templates, and it auto-generates human-friendly error messages as needed.
vetr is written in C to minimize overhead from parameter checks in your
functions. It has no dependencies.