How to write grammar rule?

[dprogm]

Hello everybody 😉

I have perhaps a simple question but cannot answer it by myself. Suppose the following grammar rules:

managed_interfaces = { "manages" ~ (ws+ ~ (interface | fqn)) ~ (ws* ~ "," ~ ws* ~ (interface | fqn))* }

interface = { "interface" ~ ws+ ~ id ~ (ws+ ~ "extends" ~ (ws+ ~ (interface | fqn)))? ~ managed_interfaces? ~ "{” }

The problem is that I want to require whitespace before managed_interfaces if the last group ends with an fqn or is not present at all and optional whitespace in case of an interface. I don't know exactly how to express this in a clean and readable way.

Any tip is appreciated ☺️

[tomtau]

Maybe splitting the interface rule into two rules: one for when it ends with fqn or is not present at all (with mandatory whitespace), and another for when it ends with interface (with optional whitespace)?