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If you are using a library with this kind of number representation, computing any rational number with a repeating decimal representation will use up all your memory. 1/3=0.33333… It will keep allocating memory to store infinite copies of the digit 3. (In practice it stores it using binary representation but you get the idea.)

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For the Rust crate, there is already an arbitrary limit (defaults to 100 digits) for "unbounded operations" like square_root, inverting, division. That's a compile time constant. And there's a Context object for runtime-configuration you can set with a precision (stop after `prec` digits).

But for addition, the idea is to give the complete number if you do `a + b`, otherwise you could use the context to keep the numbers within your `ctx.add(a, b)`. But after the discussions here, maybe this is too unsafe... and it should use the default precision (or a slightly larger one) in the name of safety? With a compile time flag to disable it? hmm...

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