Hi all,

The attached program exhibits some odd behavior in 2htdp/universe, and I want 
to track down where it’s coming from. AFAICT it’s not an error in the program 
itself, but if I’m mistaken I’d be pleased to have confirmation that the cause 
isn’t in the OS or the 2htdp/universe library.

Here’s how to reproduce the behavior I’m seeing, which is on OS X 10.11.6:

1. Run the program
2. Hold down one of the two Shift keys
3. Hold down the other Shift key
4. Release one of the keys
5. Release the other key

Expected behavior: After step 4, one of the keys reverts to its #false state; 
after step 5, both are #false.

Actual behavior: Step 4 does not provoke a change in the program’s state. After 
step 5, the last-released key reverts to #false.

Does this occur on other platforms or other verions of OS X? Do you see a 
problem I’m missing in the program?


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Attachment: tracking keypresses.rkt
Description: Binary data

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