code: func (p *Planner) planExpr(e *ast.Expr, iter planiter) error {
  
  	if e.Negated {
  		return p.planNot(e, iter)
  	}
  
  	if len(e.With) > 0 {
  		return fmt.Errorf("with keyword not implemented")
  	}
  
  	if e.IsCall() {
  		return p.planExprCall(e, iter)
  	}
  
  	return p.planExprTerm(e, iter)
  }
docs: // TODO(tsandall): improve errors to include location information.