[lively-kernel] data binding setters / why no infinite recursion?

Davide Della Casa davidedc at gmail.com
Tue Sep 16 01:10:41 CEST 2014

In the Celsius - Fahrenheit example, each text box is connected to the other one.

So changing the Celsius calculates the Fahrenheit and vice-versa.

Question is: why does it not go in infinite updates between the two text boxes?

I’m going through the code and “How connect works” and can’t figure out what’s preventing the infinite updates. The original Ingalls 1988 Fabrik paper mentions that this loop can/should/is avoided but it doesn’t give specifics (“with some care” and “bidirectionality…shorthand for multiple paths” page 5). There doesn’t seem to be a check in “connect” or “update” or the setter. The setter seems to do an update, so why doesn’t changing the C box cause the setter of F to invoke updates on C again?

Also tried to look for “loop” in source code https://github.com/LivelyKernel/LivelyKernel/search?utf8=%E2%9C%93&q=loop&type=Code but nothing jumps to the eye.

What’s the trick I’m missing?

(BTW the edit/select/move-cursor behaviour in the text boxes when they are connected is glitchy)

Davide Della Casa

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