Lazy in racket

How2lazy in DrRacket?

There's the lazy library, but it's not functional, i.e. I define a to be 1, define b as a + a, force b, it gives 2, but then I force set a to be 5, and it gives b as 2 again.

Any way around this?

>>8
Heh, I was thinking "Scheme" as in "the way the interpreter (and theory) worked in the SICP videos"
Yes, it's different, but that's because you'd need to re-evaluate everything.
What if the promise had some side effects? They would be evaluated twice and that's not an acceptable behaviour.