Is this correct grammar for Nearley?

Question

Is the following good grammar for Nearley.js? It describes logical expressions with variables, negation, conjunction and parentheses.

It's a bit convoluted (?), but I didn't know other way how to make precedence work.

expression -> _ conjunction _      {% function(d) { return d[1] } %}

# Parentheses
parens ->
  "(" _ conjunction _ ")"          {% function(d) { return d[2] } %}
| variable                         {% id %}

# Negations
negation ->
  "~" _ parens                     {% function(d) { return {negation: [d[2]]} } %}
| parens                           {% id %}

# Conjunctions
conjunction ->
  conjunction _ "/\\" _ negation   {% function(d) { return {conjunction: [d[0], d[4]]} } %}
| negation                         {% id %}

# Variables
variable -> [A-Z]                  {% function(d) { return {variable: d} } %}

_ -> [\s]:*                        {% function(d) { return null } %}