Some basic ABNF parsing functions for use with fty::defresult.
These functions may be be useful when writing fty::defresult-based parsers for languages specified via ABNF grammars. These functions take lists of natural numbers as inputs and return two outputs: (i) a fty::defresult value (e.g. tree or error) obtained from the consumed input natural numbers, and (ii) the remaining unconsumed input natural numbers.
These are somewhat similar to the Seq-based parsing primitives, but they have an interface suitable for fty::defresult instead of an interface suitable for Seq.