Where do stars live? Thats what I wonder.
Inverse Parentheses
11–20 of 67 posts
Re: Inverse Parentheses
#12The concept of "inverse parentheses" that unbundle operators is brilliant! The tokenizer hack (friendliness score by parenthesis depth, inspired by Python INDENT/DEDENT) + precedence climbing for infinite levels is elegant – parsing solved without convoluted recursive grammar.
kellett
I love the twist: reversing the friendly levels gives you a classic parser, and it opens up crazy experiments like whitespace weakening. Have you tested it on non-arithmetic ops (logical/bitwise) or more complex expressions like ((()))?
Re: Inverse Parentheses
#13I was hoping the parentheses themselves would be flipped. Like this: > 1 + )2 * 3( (1 + 2) * 3
I think surrounding the operand would make slightly more sense, as in 1 + 2 (*) 3 as if it's a "delayed form" of the operation that it represents.
Re: Inverse Parentheses
#14Echoing the sentiment that I'm not really sure what I'm meant to be looking at here. A motivating example at the start would have helped, I think.
Re: Inverse Parentheses
#15Opened this excitedly, thinking I was going to get something related to S-expressions/Lisp, was disappointed...
Re: Inverse Parentheses
#16Using Brave on MacOS, I cannot scroll the page to see the entire text. On Firefox, it scrolls fine.
Splendid. Someone found a way to break Browser Scrolling. (Firefox 115.16 for Win7)
Well done.
Re: Inverse Parentheses
#17Am I stupid if I don't get it? What is the intended end state? What does "ungroup operands" mean?
Re: Inverse Parentheses
#18Am I stupid if I don't get it? What is the intended end state? What does "ungroup operands" mean?
I'm not sure I'm following but I think what he means is that if normal parenthesis around an addition mean this addition must precede multiplication, these anti-parenthesis around a multiplication have to make addition take place before it.
Re: Inverse Parentheses
#19Parenthesis used to decrease precedence? Everything outside of the parenthesis will be done before what is in the parenthesis?
Re: Inverse Parentheses
#20Based on this comment (https://news.ycombinator.com/item?id=46352389), I think I understood the missing first paragraph:
If you have the expression 1+2*3 you have three elements with two operands. You need to choose a rule to pick one of them first.
In mathematics, the rule is "*/ then +-" and then from left to right. This means that usually first you do 2*3, then 1+.
But what if you do want to make 1+2 first?
There is another alternative, parenthesis. Those mean "do the thing inside first" so (1+2)*3 changes the precedence and now you do 1+2 first, then *3
The post is asking: with parenthesis you can increase the precedence of operations. What if you could decrease it?
Let's use «» as another operand (the blog uses parenthesis, but that makes it really confusing) this operand means "do the thing inside last". So the expression 1+«2*3» means "do 1+ first, then 2*3.
The issue is...this doesn't make sense, what the blog is really saying is to reduce the precedence of operators. Think the expression 1+2«*»3 or 1+2(*)3 and now the rule is "the parenthesized operators have one precedence less" so 1+2(*)3=(1+2)*3