[Mathlib-develop] Should NumberToken be immutable?

[mark <msp...@ya...>]

At the moment when executing num1 <op> num2 the system sometimes modifies=
 num1=20
and sometimes creates a new NumberToken.

I've been thinking that it might be better if NumberTokens were immutable=
 so=20
that all operations returned a new object without changing either operand=
=2E

The advantages are
1: constants can be used in place of common numbers (-1,0,1,i)
2: this will reduce the need for functions to clone there parameters befo=
re=20
operating on them=20
3: it'll reduce the chance of bugs becuase of having two references to a=20
number that suddenly changes

The disadvantages are
1: It might slow some operations down

So what does everyone think about this?

Best Regards

Mark