CSC151.01 2006S, Class 17: Recursion with Files

Admin:
* Reading for Monday: Preconditions and Postconditions
* Due: HW7.
* Distributed: Exam 1 (due next Friday).
* Sorry about the confusion on Wednesday's lab.
* EC
  * No Tuesday Extra next week.
  * Is anyone participating in local events this weekend and wants 
    classmate support?
    * Vince opens for some random band (a Dead Ship) on Saturday
      Bobs.  About 9:00 p.m.
* Sam available today 10:00-12:45, 2:15-3:05.
* Sam gone until Sunday.  Prof. Davis substitutes via email.

Overview:
* About the exam
* About files.
* Key file operations.
* File recursion.
* Lab.

/About the Exam/

* See the exam for details.
* What readings?
  * Everything up to and including Files

/File Operations/

* (read INPUT_PORT) - reads first thing from the source
* (peek-char INPUT_PORT) - peeks at, but does not read, the next character
  in the source
* (read-char INPUT_PORT) - reads the next character
* (open-input-file STRING-THAT-NAMES-THE-FILE) - gives you back something you can apply read and peek-char to
  (define source (open-input-file STRING-THAT-NAMES-THE-FILE))
  (proc (open-input-file STRING-THAT))
  (define proc
    (lambda (source)
* (close-input-port INPUT-PORT) - we're done with the file
* (eof-object? VALUE) - true or false, depending on whether or not its the end of file object
  (define eof? 
    (lambda (input-port)
      (eof-object? (peek-char input-port))))
* Lots of stuff for writing, which we'll ignore right now

Pattern of recursion
(define rec-proc
  (lambda (values)
    (if (simple-enough-to-do-the-base-case values)
        (base-case)
        (recurse on a simpler case))))

(define rec-file-proc
  (lambda (input-port other-values)
    (if (eof? input-port)
        (close-and-return input-port (base-case))
        (combine (read input-port) (rec-file-proc input-port other-values)))))

(define close-and-return
  (lambda (input-port return-value)
    (close-input-port input-port)
    return-value))