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Teaching Software CorrectnessMay 13-15, 2008, University of

Oklahoma

Rex Page, U Oklahoma page@ou.edu

AssistantsCarl Eastlund (lead), Northeastern U cce@ccs.neu.eduRyan Ralston, U Oklahomastrawdog@ou.eduZac White, U Oklahomazacwhite@gmail.com

http://www.cs.ou.edu/~rlpage/SEcollab/tsc

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Collaboration with Matthias Felleisen - NSF/DUE 0633664, 0813529, 0632872

Session 06 — 9:00-9:45, May 14

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File-I/O in ACL2or …

the unbearable ugliness of stateor …

how multiple values can ruin your vacation

plusDrACuLa's GUIs

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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

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Multiple Valuesanother 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 ormultiple-value (with any number of components)

associates

value-i w

ith sym

bol-

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

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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 forceMust deliver state

– Either as an ordinary value– Or, as part of a multiple value

The symbol “state” denotes the current ACL2 stateYou 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

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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) (filestring 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

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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 haveUnix-style lines

dos2unix "code.scm"

list-utilities

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Utilities TeachpacksUtilities 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/

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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 eventsMouse 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 xstart ystart xend yend color) … etc …

DrACuLa kicks it off(big-bang width height seconds-per-tick initial-world )

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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

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Canvas update function: worldimage 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 worldimage)

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" functionwith redraw event

deconstructor for m-world struct(automatic with defstructure)

(on-redraw draw-balls)formula placed in source code after definitions

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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

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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

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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

disappearhttp://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

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The End