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by seiji 3772 days ago
That's a very HN comment. Completely wrong but delivered with strong convictions.

Lisp doesn't actually exist. Lisp is just axioms. You run an implementation of Lisp allowing various operations. Some flavors actually have (practically) zero mutability. You just create functions and cons cells and the rest of the world gets built on top of those.

But, pure functional systems are useless (to be purely functional would mean you can't even do I/O... your program would just heat up the computer, which, in a way, is its own form of output, so you can't ever be fully functional).

Every functional language gets non-functional at some point for data processing, bootstrapping, loading/saving programs, and the best functional languages even have optional mutability constructs for performance (see: !). You can't create the most performant data structures possible if all your operations require path copying, but mutability should be reserved for internal high performance library creation and avoided in business logic/application level code to make systems easier to reason about.
2 comments
mbrock 3772 days ago
"Lisp doesn't exist" is also kind of wrong but with conviction, or at least debatable. Lisp was standardized in 1994 as ANSI Common Lisp, and there are a handful of other Lisp-like languages.

And pure languages aren't useless. Not being able to do I/O can be good for many purposes. Pure Haskell is still able to model computations involving I/O, which are then executed by a trusted external runtime. There are benefits to disallowing arbitrary effects, which is also why several new languages take purity even further and disallow infinite recursion.

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catnaroek 3772 days ago
For clarification, in a deduction system, an axiom is a proposition that is true just because. Similarly, an axiom schema is a predicate, such that substituting its free variables with closed terms yields a proposition that is true just because.

Now, I repeat, how exactly is Lisp “just axioms”? What are the axioms in question? The mathematical ignorance of some of Lisp's proponents never ceases to amaze me.

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