string=???

[Libby Miles]

My teaching partner and I have stared at this for an hour. What are we missing? I'm so desperate for an answer for my student in second period tomorrow. Thank you if you can help!!

(EXAMPLE (update-player 320 "up") (+ 320 20))

(EXAMPLE (update-player 100 "up") (+ 100 20))

(EXAMPLE (update-player 200 "down") (- 200 20))

(EXAMPLE (update-player 120 "down") (- 120 20))

(define (update-player y key)

(cond

[(string=? key "up") (+ y 20)]

[(string=? key "down") (- y 20)]

[else y]))

yields the error message

string=?: expects a string as 1st argument, but given: 1; other arguments were: "up"

[Emmanuel Schanzer]

Hi Libby - I just copied and pasted your code into a blank WeScheme window, and I get no error message. I think the error you’re seeing is coming from elsewhere. Can you click “share”, and paste the link to the entire program here?

Sent from my iPhone. May appear unintentionally terse.

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[Libby Miles]

Yes, here it is, thank you!! https://www.wescheme.org/openEditor?publicId=fvin3zdiUN#

[Mark Engelberg]

 [(string=? "key" "up") (+ y 20)]

The "key" shouldn't be in quotes.

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[Emmanuel Schanzer]

I’m still not seeing that error. (I’m seeing other errors, but not the one you’re posting about.)

Your update-player is definitely looking a little strange...id say keep working on it, and be sure to check out the examples that are failing. But there is no problem with string=? in this code.

[Emmanuel Schanzer]

Oh!! Great catch, Mike!!!

Yes - something has gotten messed up on line 177. Libby, your student has been messing with some of the provided code. :)

Update-player has been written twice. Can you see what your student changed? And what it should be?

[Libby Miles]

Emmanuel, I just tried the link I sent you and realized that, in that link, there were still quotations around "key" in the definition, which I erased. Then you get my error message. I don't know what you mean by keep working on it - I even copied and pasted update-player from another student's working game and got the same error message. I have checked all the code above and can't find the mistake and so has my colleague. Why are you saying that the code looks a little strange - was it just those quote marks? 

I can just tell the students to start over on a new game template if you think that will help, but I'm out of other ideas. 

Thanks a bunch

[Emmanuel Schanzer]

Have you seen like 177? Your student has been messing around with some of the provided code. Compare that to another student’s program and you’ll see what I mean. :) 

Sent from my iPhone. May appear unintentionally terse.