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Scheme certainly has mutability, through set!, set-car!, set-cdr!, and procedures based upon them. It's not the default - you always know when you're mutating something - but then, there's a pretty direct syntactic translation into Javascript, where = without a var always means you're mutating something.

Why is this important for students, anyway? Shouldn't they be exposed to mutability fairly early on?

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It's not important for students, I just dispute the notion that JavaScript has any special affinity with Scheme beyond that of any other language with first-class functions. Anyway, the major advantage of immutability by default is that it enables under-the-hood optimizations like structural sharing that make FP the paradigm of least resistance. To the extent that JavaScript doesn't do that, it doesn't really deserve to be called a functional language any more than e.g. Ruby.

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