code: func StringSliceOperand(x ast.Value, pos int) ([]string, error) {
  	a, err := ArrayOperand(x, pos)
  	if err != nil {
  		return nil, err
  	}
  
  	var f = make([]string, len(a))
  	for k, b := range a {
  		c, ok := b.Value.(ast.String)
  		if !ok {
  			return nil, NewOperandElementErr(pos, x, b.Value, "[]string")
  		}
  
  		f[k] = string(c)
  	}
  
  	return f, nil
  }
docs: // StringSliceOperand converts x to a []string. If the cast fails, a descriptive error is
  // returned.