<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"><base href="x-msg://2355/"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">I asked Marty to send me a copy of his code… This is my reply him, but it demonstrates a problem using DoTogether which happens frequently, and is very difficult to overlook and track down.<div><br></div><div>See the attached screen shot, from the method "world.KeepScore":<div><br></div><div>The code of concern is this doTogether, in which you are (1) setting the value of the variable 'animalThatWasHit', (2) printing that value, and (3) sending that value as a parameter, AT THE SAME TIME.</div><div><br></div><div>A do together generates separate, independent threads for each statement in the doTogether body, and so what is happening in one statement may or may not, depending on the timing, have any impact on the other threads, particularly if they are trying to use the same variable.</div><div><br></div><div>So it is not so much that the value reverts to paintball, but that you print as the value is being set. If you had printed it again, after the doTogether, you would have seen the correct result.</div><div><br></div><div>I dissolved the doTogether and got the following output after running the program:</div><div><br></div><div><strong><span class="Apple-tab-span" style="white-space: pre; "> </span>tiger</strong></div><div><strong><span class="Apple-tab-span" style="white-space: pre; "> </span>none</strong></div><div><strong><span class="Apple-tab-span" style="white-space: pre; "> </span>tiger</strong></div><div><strong><span class="Apple-tab-span" style="white-space: pre; "> </span>none</strong></div><div><strong><span class="Apple-tab-span" style="white-space: pre; "> </span>tiger</strong></div><div><strong><br></strong></div><div>I hope that this helps… </div><div><br></div><div>This is a very difficult bug to track down, one that even experienced Alice programmers. will make. It is easy to overlook (you did not even think to include the doTogether's in your pseudocode, and yet they are critical) and not think about.</div><div><br></div><div>Look at how different your pseudocode looks if you had written it this way</div><div><br></div><div><blockquote type="cite"><div lang="EN-US" link="blue" vlink="purple"><div class="WordSection1" style="page: WordSection1; "><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; ">Method world.keepScore looks similar to:</div></div></div></blockquote><span class="Apple-tab-span" style="white-space:pre"> </span>DoTogether<br><blockquote type="cite"><div lang="EN-US" link="blue" vlink="purple"><div class="WordSection1" style="page: WordSection1; "><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> // precondition: Local variable animalThatWasHit (type=OBJECT, initial value set to paintball)<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> 20 animalThatWasHit set value to world.whoGotHit<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> 20 print animalThatWasHit<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> 20 world.whenHit target=animalThatWasHit</div></div></div></blockquote></div><div><br></div><div>All the best,</div><div>Don Slater</div><div><br></div><div><img height="299" width="661" apple-width="yes" apple-height="yes" id="3c4e784f-cede-4b8c-bb1a-e0d525ed846d" src="cid:CBABCBFD-BE94-44A7-A156-078BAABBC09B@wv.cc.cmu.edu"></div><div><br></div><div><br><div><div>On Apr 14, 2013, at 9:48 PM, Marty Schultz <<a href="mailto:schultz_marty@hotmail.com">schultz_marty@hotmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div lang="EN-US" link="blue" vlink="purple" style="font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div class="WordSection1" style="page: WordSection1; "><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; ">Does anyone have a solution for this (I’ve included pseudo line numbers to make it clear):<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; ">Function world.whoGotHit (returns type OBJECT) ends with:<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> 10 print “world.whoGotHit”<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> 11 print tiger.name<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> 12 return tiger<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; ">Method world.keepScore looks similar to:<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> 20 Local variable animalThatWasHit (type=OBJECT, initial value set to paintball)<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> 22 animalThatWasHit set value to world.whoGotHit<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> 23 print animalThatWasHit<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> 24 world.whenHit target=animalThatWasHit<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; ">Method world.whenHit<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> 30 parameter target (type=OBJECT)<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> 32 print “world.whenHit”<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> 33 print target<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; ">When I PLAY this program, the PRINT statements show:<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> world.whoGotHit (from line number 10)<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> tiger (from line number 11)<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> the value of world.keepScore.animalThatWasHit is tiger (from line 23 – this is expected)<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> world.whenHit (from line 32)<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> the value of world.whenHit.target is paintball (from line 33- this seems WRONG – it should be “tiger”)<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; ">What appears to be happening is that even though the value of animalThatWasHit is “tiger” in the world.keepScore method, when the world.whenHit method is called, the value reverts back to the initial value, not the value shown in the parent (world.keepScore) method.<o:p></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; "> <o:p></o:p></div></div>_______________________________________________<br>alice-teachers mailing list<br><a href="mailto:alice-teachers@lists.andrew.cmu.edu" style="color: purple; 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