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If you were a non LISP programmer and thought "Fibonacci using recursion", you might think you'd have something like fib(a)=fib(a-1)+fib(a-2), and scoff at its

If you were a non LISP programmer and thought "Fibonacci using recursion", you might think you'd have something like fib(a)=fib(a-1)+fib(a-2), and scoff at its possible performance, and also wonder how that would be tail call optimized. But as a LISP programmer, you'll think of this in the way a Java programmer would think of a loop, and just treat this as a count over two values n times, adding along the way. And this is why I don't like LISP: because I have programmed assembly and built up from there, and doing loops using tail call recursion seems to be a lie. It is a faulty abstraction. It is a loop. You'd be better off doing it in a loop, in any sane language, and if you do it right in LISP, the code will generate a loop in assembly language. Just the fact that this thread devolved into how to specify compiler options so that it actually generates that loop shows how absurd the whole thing is.

oconnor663 5y ago
I think the appeal of expressing loops with recursion is that it lets you to avoid mutation. But I agree with the point that Rust folks frequently make, about how being able to mutate things safely is a lot nicer than avoiding all mutation.
dTal 5y ago
Do "for" and "while" constructs also seem silly? After all they "compile to a loop" as well. The purpose of all these loop constructs is to place constraints on some essential aspect of the loop up front, thus narrowing the possible range of effects of that wicked goto, by encoding common patterns. "For" loops guarantee the number of iterations. "While" loops guarantee the exit condition. And tail recursion guarantees what state gets modified in the loop. It is strange the way you say "better off doing it in a loop". As you say, it is a loop. What construct would you prefer? GOTO?
dunefox 5y ago
And where exactly is the problem with the compiler rewriting tail calls into a loop on the assembly level? Calling this a "lie" is pretty childish.

oconnor663 5y ago

I think the appeal of expressing loops with recursion is that it lets you to avoid mutation. But I agree with the point that Rust folks frequently make, about how being able to mutate things safely is a lot nicer than avoiding all mutation.

dTal 5y ago

Do "for" and "while" constructs also seem silly? After all they "compile to a loop" as well. The purpose of all these loop constructs is to place constraints on some essential aspect of the loop up front, thus narrowing the possible range of effects of that wicked goto, by encoding common patterns. "For" loops guarantee the number of iterations. "While" loops guarantee the exit condition. And tail recursion guarantees what state gets modified in the loop. It is strange the way you say "better off doing it in a loop". As you say, it is a loop. What construct would you prefer? GOTO?

dunefox 5y ago

And where exactly is the problem with the compiler rewriting tail calls into a loop on the assembly level? Calling this a "lie" is pretty childish.