undefined | Better HN

0 pointsjeffreygoesto3y ago0 comments

Somewhere down towards the transistors, the change has to happen. The registers of the machine are explicitly designed to be mutable. I don't know how functional languages are compiled and maybe somebody who does can chime in, but I would not be surprised if the IR already was imperative. So it may be easy to give some access to that in a language.

I'd say "pure" is if the calculation can be done with a function without side effects and it is a deliberate choice to restrict a language to (almost) only that. No side effects at all would mean no interaction with "the outside world" and no access to input data though.

0 comments

3 comments · 2 top-level

kaba03y ago· 1 in thread

Haskell compiles down to C- first, which is an even less expressive version of C basically, so you are right there.

But if you go low enough FP concepts pop up again, e.g. out-of-order execution is pretty functional, but to a degree so are vector instructions. And this is no surprise, Turing machines and lambda calculus (and recursive functions and anything Turing-complete) are equivalent. If you think about it, a Turing machine is just as side-effect free in itself, side effects are special to computers.

jeffreygoestoOP3y ago

Deep down it must be, as the data is conveyored past fixed compute engines (which can be seen as pure functions), right? FPGA programming is pretty much functional as well. RAM is capturing the state there.

zelphirkalt3y ago

We can see FP as a tool to for us to express a functional thought so that the computer can understand it and will translate it into something the computer itself can run.

j / k navigate · click thread line to collapse