How do "_" rules work?

[piegamesde]

I don't understand this rule:

_ or __ or ___ - Rule (underscore): As a special case, rule names consisting of underscores are invoked without parentheses. These are conventionally used to match whitespace between tokens.

If I read the definition correctly, I need to call my rule _ and then it will work?

rule _ = skip_whitespace()

however gives me:

error: expected one of "(", "<"
  --> src/placement.rs:43:16
   |
43 |         rule _ = skip_whitespace()
   |                ^

error: aborting due to previous error

[mdenchev]

You only omit the () when invoking, not when defining. So it would be:
rule _() = skip_whitespace()

Example:

rust-peg/benches/json.rs

Line 14 in 3d4cd82

rule _() = [' ' | '\t' | '\r' | '\n']*

[piegamesde]

Yeah, that makes sense, thanks. Maybe add that line somewhere as an example in to the documentation, please?

[kevinmehall]

We should probably just make it accept the more obvious rule _ = syntax here.