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Haskell, Reverse Polish Notation, and Parsing

69 points by mw_1

by jcalvinowens

2 subcomments

I've always felt like RPN is a really powerful lesson in how subtly redefining the semantics of a problem can make it suddenly much easier to solve.
My personal struggle with functional programming is how difficult I find it to be iterative. I've very frequently backed myself into a corner and ended up having to rewrite everything, whereas in C, even when I miss badly on the architecture, I'm still usually able to reuse some big chunks of what I've already done in the end. Maybe it's just inexperience.

by kibwen

4 subcomments

Agreed that RPN (and stack machines) are beautiful and underappreciated. Unfortunately, it's for a relevant reason that I have to push back against the author's newfound love of recursion. Like everyone else I had the same brain-exploding moment when I realized that recursion was possible and how if forced me to re-think what functions were capable of, but now that I'm old and ornery I'm of the Hot Take that recursion is a clumsy alternative to a loop, not the other way around. Which is to say, if a portion of a program is going to threaten to execute for an unbounded amount of time, I want that fact to be explicitly called out in the code via a looping construct, rather than having to worry whether any random function call is going to recur (or even mutually recur), to say nothing of the efficiency of holding onto a single piece of loop-relevant mutable state rather than forcing my runtime to handle an unbounded number of stack frames. If your language both guarantees tail recursion and calls it out syntactically, then you get a pass, otherwise I'd be perfectly happy working in languages that didn't support recursion at all.

by jacksonslipock

1 subcomments

Made me feel like I understand monads finally...will read again in a couple days when I inevitably forget.