Problem with scope of objects
Locked
Problem with scope of objects
 
|
Re: Problem with scope of objects
|
|
Hello Christian,
I think that perhaps the "tutorial" you were looking at might not be the best way to get started with etoys. First of all, to get a classic "Hello World" built in a Squeak project, there's no need to open a Viewer, nor to create or run a script. If you want a project which, when loaded, displays the text "Hello World" (this is the classic definition of a "Hello World" program, I believe,) you can simply obtain a fresh "text" object from the supplies flap, then click to select the word "text" and then type to replace its contents with the words "Hello World". If desired, resize the text object using the yellow resize handle. Then save the project, and you're done. This is not a programming task, but rather simply a get-to-know-the-environment task. If for some reason you're intent on using a tile script to set the contents of the Text object, rather than simply directly editing the contents as described above, you can indeed pursue the approach suggested in that tutorial. However, the tutorial's instruction that you click the checkbox in the Scriptor's header to change it from tile mode to textual mode seems to be what's leading you astray here. There's no reason to go to "textual mode" -- the task at hand is easily accomplished staying in tile mode, by simply text-editing the word "Text" to the right of the arrow in the script into the wording "Hello World": Finally, I would guess that the problems you're having with object- reference are because you are trying to refer to other objects by typing their names into textual code in textual scripts. You should really stick to tiles, particularly until you've mastered the basics of tile scripting! In the case of the classic drive-a-car demo, when you want "Car turn by 5" in a script to become "Car turn by Wheel's heading", you open Wheel's Viewer, grab "Wheel's heading" tiles from the Viewer, and drop them on the "5". Also, you can use the orange "tile" handle in the halo of an object to "tear off a tile" that refers to that object. Drop that tile onto any reference tile anywhere in any script and it will replace that tile. What you were trying to do was probably to type a textual script in which you guessed at what the internal name used to refer to a particular object might be -- but this is not a reliable approach, since there is no restriction made on the format of external object names, nor any requirement of uniqueness, with the result that Squeak internally uses a regime of "internal names" which are syntactically acceptable and unique, and there is no guarantee of correlation between visible names and internal names. So the bottom line is: use tile scripts rather than textual scripts. Use drag-and-drop, rather than typing. All of the introductory etoys materials that I'm aware of (other than the tutorial you ran across) operate strictly with tiles. Textual scripting provides a great "escape" which opens up the entire universe of Smalltalk programming to the advancing user, but textual scripting certainly should play no role in "Hello World", nor in "Drive a Car", nor in any other introductory projects. If this does not properly address your concerns, please ask further! Cheers, -- Scott On Nov 12, 2007, at 8:50 PM, Christian Bode wrote: > Hi, > > I am german cs student getting more and more amazed about squeak. > Tonight I began to play around a bit and wanted to do that amazing > "draw and steer your car" thing :) > > I used this tutorial to get started: > http://www.dmu.com/squeak/sq0.html > > Well, unfortunately i could not figure out this simple thing in 3 > hours. > My problem is, after having added the car "Speedy" to the world, I > cannot > reference to it from any other script. If I add a steerwheel to the > world, and > want attach a script to it, squeak is not able to resolve that > reference. It will > tell me that "Speedy" is undefined and ask me if I would like to > declare > it global or create it. > I had this problem with all kinds of things; text fields, button > etc. I could > not manage to get the "Hello World", from the tutorial running > (http://www.dmu.com/squeak/sq1.html). > > Did I get something wrong ? So before I loose interest I rather ask. > I am > puzzled because I did it exactly the way described in the tutorial. > > Thank you a lot! > Frederick (That´s a nick, if you wonder :)) > > _______________________________________________ > Squeakland mailing list > [hidden email] > http://squeakland.org/mailman/listinfo/squeakland _______________________________________________ Squeakland mailing list [hidden email] http://squeakland.org/mailman/listinfo/squeakland |
Re: Problem with scope of objects
|
|
Re: Problem with scope of objects
|
|
Re: Problem with scope of objects
|
|
Re: Problem with scope of objects
|
|
Re: Problem with scope of objects
|
|
Re: Problem with scope of objects
|
|
In reply to this post by Luke Gorrie-3
On Nov 13, 2007, at 12:24 AM, Luke Gorrie wrote:
> > ...P.S. Any suggestions on more examples or documentation for > advancing users? There is not much available about textual scripting. However, here are a few notes that should help anyone who knows a little Smalltalk get started with textual scripting: (1) The "self" of a textual script is a *player* object, whose corresponding "morph" is found as its costume. A (very annoying) complication is that if the morph has been rotated (i.e. its heading is not 0), the costume referred to in the player is actually not the original morph (e.g. a JoystickMorph, SketchMorph, or whatever it was that you started with) but rather a TransformationMorph which holds the rotation info and which is the "owner" of the actual morph. If you have a script for some SketchMorph and you wish, in a textual script, to refer to the SketchMorph, and to be certain that the script still works if the SketchMorph is subsequently rotated, use the (very annoying) idiom "self costume renderedMorph" -- this will always get to the Morph you're most likely wishing to talk to in a textual script. (2) If in your script you wish to refer to the "World" morph, you can use the global name "ActiveWorld". (3) To refer to any "variable" belonging to the player, as seen in the "variables" section of its Viewer, use the special "getter" and "setter" idioms: for example, to get a player's heading, send it "getHeading", and to *set* the player's heading to 5, for example, send it "setHeading: 5". Similarly, for the variable "x" it would be "setX" and "getX", and so forth. (4) Keep a Transcript open when you're doing textual scripting, to see reports of "runtime errors", i.e., errors that arise in executing your textual scripts; otherwise these will be simply swallowed silently. ------ Here's a simple example of textual script, itself of no value except to show how you can enumerate and identify objects and interact with objects on the screen. Set it to ticking and it will gradually nudge all objects (except flaps) to the right of the screen: ------ Here's a less trivial example, which does something that is otherwise very difficult to do with tiles. The Shark (a little star) has a "player-valued" variable called "nearestFish". The shark's "findNearestFish" script is a textual script that first makes a list of all the non-sharks in the aquarium, then computes which of them is *nearest* to the shark, and, finally, places a reference to that nearest fish in the Shark's "nearestFish" variable, where it is subsequently used by the shark's "pursue" script. As the simulation advances, you can see whom the Shark regards as its nearest fish by looking at the "Shark's nearestFish" watcher found below the aquarium. The little triangular fish are all "siblings" running the same "meander" script. The third and final script in the project is the shark's "pursue" script, which makes the shark move toward whichever fish he considers the nearest at the moment. Here's a (low-res) picture of all the components of this example: I also attach a copy of the actual project. which was created using the existing Squeakland system but will load and run equally well in an olpc etoys system. Cheers, -- Scott _______________________________________________ Squeakland mailing list [hidden email] http://squeakland.org/mailman/listinfo/squeakland  pastedGraphic.tiff (232K) Download Attachment pastedGraphic.jpg (218K) Download Attachment findNearestFish.001.pr (104K) Download Attachment |
| Free forum by Nabble | Edit this page |