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>you are free to ignore the things you don’t understand

Is that why you are ignoring the complexity behind persistence/mutability/state?

Even the Abstract Turing machine has ticker tape you know...

Interesting point. Lambda calc is equivalent, where the expression can be seen as equivalent to the ticker tape. So when a reduction occurs in lambda calculus, it's just like a group of symbols being interpreted and overwritten. But the thing is, no one has to overwrite the symbols to "reduce" them. It's just a space (memory) optimization. Usually to calculate something (you're fully correct by the way) we do overwrite symbols. The point of using immutable style is simply to make sure that references don't become overwritten. It sucks to have x+2=8 and x+2=-35.4 within the same scope, right? Especially when the code that overwrote x was in a separate file in an edge case condition you didn't consider.

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