Returns true if the input source is in the language defined by
the grammar.
Returns error.MaxDepth if more than max_depth levels of recursion/iteration are reached.
pub fn parse(source: []const u8) Error!bool
pub fn parse(source: []const u8) Error!bool {
var p: Parser = .{ .source = source, .i = 0, .depths = @splat(1) };
return p.parseRoot();
}