Parse one or more expressions with helpful errors

I'm using grako (a PEG parser generator library for python) to parse a simple declarative language where a document can contain one or more protocols.

Originally, I had the root rule for document written as:

document = {protocol}+ ;

This appropriately returns a list of protocols, but only gives helpful errors if a syntax error is in the first protocol. Otherwise, it silently discards the invalid protocol and everything after it.

I have also tried a few variations on:

document = protocol document | $ ;

But this doesn't result in a list if there's only one protocol, and doesn't give helpful error messages either, saying only no available options: (...) document if any of the protocols contains an error.

How do I write a rule that does both of the following?:

1. Always returns a list, even if there's only one protocol
2. Displays helpful error messages about the unsuccessful match, instead of just saying it's an invalid document or silently dropping the damaged protocol

This is the solution:

document = {protocol ~ }+ $ ;

If you don't add the $ for the parser to see the end of file, the parse will succeed with one or more protocol, even if there are more to parse.

Adding the cut expression (~) makes the parser commit to what was parsed in the closest option/choice in the parse (a closure is an option of X = a X|();). Additional cut expressions within what's parsed by protocol will make the error messages be closer to the expected points of failure in the input.