How to close all files that an Applescript has opened?

Question

I'm writing a script with multiple "open for access file ... with write permission" commands. It writes to various of them, making csv databases as it works its way through analyzing an xml file (generated by other software), then closes them all at the end.
My problem is that, if the script crashes or I have to halt it before it gets to the "close" commands at the end, the files are left open. This causes an obvious error when next running the script after making adjustments.
How can I ensure that those files are always closed? At present I'm doing it by quitting and re-starting Script Editor, which leaves me disoriented in the code.
Is there a generic close command that I can insert at the start of the script, for example?

Answer 1

Use this handler to open files.  It tries to open the file, and if it gets error -49 (file already open) it closes the file and reopens it.  It returns a file pointer to the open file, which you can use to refer to the file later.
on openAFile(filePath, writable)
          try
                    set fp to open for access filePath write permission writable
          on error errstr number errNum
                    if errNum = -49 then
                              close access filePath
                              set fp to open for access filePath write permission writable
                    else
                              display dialog errstr
                              return false
                    end if
          end try
          return fp
end openAFile
set pointer to openAFile("/path/to/some/file", true)
set fileContents to read pointer
--close access pointer