Shunting-Yard Animation

▲ Shunting-Yard Animation(somethingorotherwhatever.com)

24 points by s1291 3 hours ago | 6 comments

▲ alter_igel 43 minutes ago | parent | next [-]

I'm not familiar with the algorithm and I don't see much explanation on the site (at least on mobile) but AFAICT this is turning parenthesized infix expressions into reverse Polish notation. In other words, it takes human-readable mathematical formulas and converts them into something a simple stack-based machine can compute in one forward pass.

It also appears that separate digits aren't interpreted as decimal numerals (i.e. (1)(3) is the sequence 1,3 and not 13) which can look a bit misleading.

	▲	justinpombrio 38 minutes ago \| parent [-]
		Yeah, it's a parsing algorithm for parsing infix (etc.) expressions. If you've seen a parsing library refer to "precedence climbing" or "operator precedence parsing", it's doing this (or something very similar). If you want to enter the number `13`, that should be one token, but there's no way to make a `13` token in this UI. You need to stick to single digits for this site to work correctly.

▲ abd-nh 18 minutes ago | parent | prev | next [-]

I made a basic demo of this years go: https://abdnh.github.io/shunting-yard-algorithm-demo/

▲ dcrazy an hour ago | parent | prev | next [-]

I typed `100+88/4` and the resulting output was `100884+/`. Should the algorithm be inserting a symbol to delineate operands?

	▲	justinpombrio 42 minutes ago \| parent [-]
		It treated that as `1 0 0 + 8 8 / 4` which is nonsensical, but it has no error detection so it rolled with it. Really `100` should be its own token, but there's no way to input that.

▲ IIAOPSW an hour ago | parent | prev [-]

Hold up. you can't just have the train take the parenthesis off screen and hand wave away what happens to those cars. What happens when your forced to keep the garbage of a computation because you can't delete anything?

(https://en.wikipedia.org/wiki/Reversible_computing)