Property definitions

nitc $ AOnceExpr :: defaultinit
# A `once` expression. eg `once x`
class AOnceExpr
	super AExpr

	# The `once` keyword
	var n_kwonce: TKwonce is writable, noinit

	# The expression to evaluate only one time
	var n_expr: AExpr is writable, noinit
end
src/parser/parser_nodes.nit:2128,1--2137,3