1. 1 Teaching Software Correctness May 13-15, 2008, University of Oklahoma Rex Page, U Oklahomapage@ou.edu Assistants Carl Eastlund (lead), Northeastern Ucce@ccs.neu.edu Ryan Ralston, U Oklahomastrawdog@ou.edu Zac White, U Oklahomazacwhite@gmail.com http://www.cs.ou.edu/~rlpage/SEcollab/tsc 1 Collaboration with Matthias Felleisen - NSF/DUE 0633664, 0813529, 0632872063366408135290632872 Session 06 — 9:00-9:45, May 14

2. 2 File-I/O in ACL2 or … the unbearable ugliness of state or … how multiple values can ruin your vacation plus DrACuLa's GUIs

3. 3 (variable value) parentheses delimit variable/value pairs Local Definitions with Let   Definition of break-at (defun break-at (delimiter xs) (if (or (endp xs) (equal delimiter (car xs))) (list nil xs) (let  ((first-x (car xs)) (brokn-cdr (break-at delimiter (cdr xs))) (frnt (car brokn-cdr)) (back (cadr brokn-cdr)) ) (list (cons first-x frnt) back)))) (defun break-at (delimiter xs) …) = ( up-to-but-not-incl-first-delimiter-in-xs all-the-rest-of-xs ) Example (break-at 'x '(h o m e x o n x t h e x r a n g e)) = '( (h o m e) (x o n x t h e x r a n g e)) value delivered by let  formula

4. 4 Multiple Values another ACL2 data structure  mv — the multiple-value constructor  (mv value-1 value-2 … value-n)  Displays just like a list (mv 1 2 3) displays as (1 2 3) (list 1 2 3) displays as (1 2 3)  Serves same purpose as a list  But … it isn’t a list … no car, cdr, cons  mv-let — the multiple-value deconstructor  (mv-let (symbol-1 symbol-2 … symbol-n) (mv value-1 value-2 … value-n) formula-for-value-to-be-delivered) may be ordinary value or multiple-value (with any number of components) associates value-i with symbol-i… (mv-let (a b) (mv 1 2) (mv a b (+ a b))) —displays as: (1 2 3) (mv-let (a b c) (mv 1 2 3) (+ a b c)) —displays as: 6 Examples

5. 5 State (it’s under the hood – don’t look)  ACL2 maintains a state of its world  Commands alter the state (defun f (x) (+ x 1)) —makes function f available for invocation (defthm about-f (implies (natp x) (natp (f x))) —adds theorem to logic (include-book "arithmetic/top“ :dir :system) —adds theorems to logic (set-state-ok t) —allows reference to state variable  File-system —part of the ACL2 state  Commands affecting file-system take a special form (set-state-ok t) command must be in force Must deliver state –Either as an ordinary value –Or, as part of a multiple value  The symbol “state” denotes the current ACL2 state You can’t do anything with state except –Supply it as a parameter in a command –Use it to name a value delivered by a command No-roach-motels rule : If state goes in, it must come out

6. 6 I/O function from read-utilities (to be discussed) Counting Lines of Code  Essential structure of loc function (defun loc (file-path state) (mv-let (str error state) (file  string file-path state) (if error (mv error state) (mv (loc-from-file-as-string str) state)))) state goes out ordinary function — no state state goes in

7. 7 Putting I/O Code Together (include-book "io-utilities" :dir :teachpacks) (include-book "list-utilities" :dir :teachpacks) (set-state-ok t) (defun number-of-noncomments (lines) (if (not (consp lines)) 0 (let* ((whitespace '(#\Space #\Newline #\Tab)) (stripped (drop-set whitespace (car lines)))) (if (or (null stripped) (char-equal #\; (car stripped))) (number-of-noncomments (cdr lines)) (+ (number-of-noncomments (cdr lines)) 1))))) (defun loc-from-file (str) (number-of-noncomments (packets #\Newline (str->chrs str)))) (defun loc-count (file-path state) (mv-let (str error state) (file->string file-path state) (if error (mv error state) (mv (loc-from-file str) state)))) loc-count.lisp Let's try it out Invocation: (loc-count "code.lisp" state) file must have Unix-style lines dos2unix "code.scm" list-utilities

8. 8 Utilities Teachpacks  Utilities books  (include-book "list-utilities.lisp" :dir :teachpacks)  (include-book "io-utilities.lisp" :dir :teachpacks)  (include-book "binary-io-utilities.lisp" :dir :teachpacks)  (include-book "avl-rational-keys.lisp" :dir :teachpacks)  Where to find documentation  See source code at http://www.cs.ou.edu/~rlpage/SEcollab/Tools/

9. 9 Yeah … but What about GUIs?  GUI implementation model  DrACuLa maintains a "world" (not the ACL2 world)  ACL2 functions to DrACuLa events Clock events (you can set the number of ticks per second) Keyboard events Mouse events  DrACuLa binds events to update-functions (on-tick-event world  world ) — updates world (on-redraw-event world  image) — updates canvas (on-key-event world key-event  world ) — updates world (on-mouse-event world x y mouse-event  world ) — updates world  DrACuLa graphics operations that deliver images (empty-scene width height) (place-image overlay-image x y old-image) (circle radius mode color) (add-line image x start y start x end y end color) … etc …  DrACuLa kicks it off (big-bang width height seconds-per-tick initial-world )

10. 10  Programmer chooses structure  Could be an atom — eg: number, symbol, string, …  Could be a list — eg: (position color label)  Could be a structure (defstructure my-world (component-1 (:assert (type-predicate component-1))) (component-2 (:assert (type-predicate component-2))) … )  Example — drop ball on canvas with mouse-click  mouse-demo.lisp  World data structure (defstructure m-world (click-ball (:assert (posn? click-ball))) (track-ball (:assert (posn? track-ball)))) Representing the World

11. 11  Canvas update function: world  image  Input: current world  Output: image  Action: DrACuLa paints image on canvas  Example — drop ball on canvas (defun draw-balls (w) (place-image (circle 5 'solid 'black) (posn-x (m-world-track-ball w)) (posn-y (m-world-track-ball w)) (place-image (circle 15 'solid 'red) (posn-x (m-world-click-ball w)) (posn-y (m-world-click-ball w)) (empty-scene  width   height  )))) Responding to Redraw Events (on-draw-event world  image) deconstructors for make-posn (posn-x (make-posn x y))  x (posn-x (make-posn x y))  y place-image superimposes this image (a red disk) on this one in this position connects "draw-balls" function with redraw event deconstructor for m-world struct (automatic with defstructure) (on-redraw draw-balls) formula placed in source code after definitions

12. 12  Update function: world x y event  world  Inputs current world x, y — coordinates of current mouse position event — symbol indicating event: 'move, 'button-down, …  Output: new world  Action: DrACuLa updates old world with new one  Example — drop ball on canvas (defun mouse-handler (w x y me) (let ((xy (make-posn x y))) (cond ((equal me 'move) (m-world (m-world-click-ball w) xy)) ((equal me 'button-down) (m-world xy xy)) ((equal me 'button-up) (m-world xy xy)) ((equal me 'drag) (m-world xy xy)) ((equal me 'enter) (m-world (m-world-click-ball w) xy)) ((equal me 'leave) (m-world (m-world-click-ball w)  ob  )) (t (end-of-time "This cannot happen"))))) Responding to Mouse Events (on-mouse-event world x y event  world) constructor for m-world struct (automatic with defstructure) deconstructor

13. 13  Update function: world x y event  world  Inputs current world x, y — coordinates of current mouse position event — symbol indicating event: 'move, 'button-down, …  Output: new world  Action: DrACuLa updates old world with new one  Example — drop ball on canvas (defun mouse-handler (w x y me) (let ((xy (make-posn x y))) (cond ((equal me 'move) (m-world (m-world-click-ball w) xy)) ((equal me 'button-down) (m-world xy xy)) ((equal me 'button-up) (m-world xy xy)) ((equal me 'drag) (m-world xy xy)) ((equal me 'enter) (m-world (m-world-click-ball w) xy)) ((equal me 'leave) (m-world (m-world-click-ball w)  ob  )) (t (end-of-time "This cannot happen"))))) Project (on-mouse-event world x y event  world) constructor for m-world struct (automatic with defstructure) deconstructor

14. 14 Projects  File I/O  Write a program that reads a file and writes a new one like it, but with the lines in the reverse order  Useful functions packets – list-utilities file->string – io-utilities str->chrs – list-utilities chrs->str – list-utilities reverse – ACL2 instrinsic  GUI  Modify program: click on red ball to make it disappear http://www.cs.ou.edu/~rlpage/SEcollab/Tools/mouse-demo.lisp  Lectures may be found here: http://www.cs.ou.edu/~rlpage/SEcollab/tsc/Lectures/  List of importable ACL2 books here: http://www.cs.utexas.edu/users/moore/acl2/v3-3/distrib/acl2- sources/books/Readme.html

15. 15 The End