From: "zverok (Victor Shepelev) via ruby-core" <ruby-core@...>
Date: 2024-04-03T06:35:13+00:00
Subject: [ruby-core:117422] [Ruby master Feature#20404] `2pi`
Issue #20404 has been updated by zverok (Victor Shepelev).
> This proposal is half joke, half serious.
There are several interesting things to unpack here (though I don���t see any actionable proposals). When writing/reading in Ruby some math, there are several different irky things:
1. `Math::` prefix (honestly, I never felt it totally justified, like `sin` or `cos` is obvious without any prefixes, why should we have it?..)���but at least can be mitigated by `include Math`
2. `PI` in all-caps. I understand it corresponds to the constant rules of Ruby, yet in a complicated formula, it really catches your eye as ���something I���d like to read in a less screaming manner��� (in some cases, I even introduced a local variable `��` to write some cumbersome formula)
3. The math intuition of `2<variable>` to mean `2 * <variable>`, and in some formulae, perceived as an atomic part of it
(3) in some languages (can���t remember which ones from the top of my head, but I definitely saw it) is addressed by treating `<number><identifier>` as `<number> * <identifier>`. IDK, maybe this is the way?.. Currently, `2x` is a syntax error, so there should be no conflicts.
And also... Can it be possible to introduce `Math::pi` and `Math::e` (which, by the logic of naming, should be methods, yet maybe can be treated by parser or optimizer as constants)?..
Just thoughts.
----------------------------------------
Feature #20404: `2pi`
https://bugs.ruby-lang.org/issues/20404#change-107797
* Author: mame (Yusuke Endoh)
* Status: Rejected
----------------------------------------
I propose a new Float literal: `2pi`.
```ruby
p 2pi #=> 6.283185307179586 == 2 * Math::PI
```
I am not proposing `1pi`, `3pi` or `4pi`. I do only `2pi`. Because in most cases, all you need is `2pi`. Any other multiple of pi is rarely needed.
I've got the statistics. GitHub code search revealed that more than 80% of the occurrences of `n * Math::PI` and `Math::PI * n` had n = 2. [1]
| n |`n * Math::PI`|`Math::PI * n`|sum | % |
|--:|-------------:|-------------:|----:|---:|
| 0 | 48| 1| 49|1.4%|
| 1 | 58| 3| 61|1.7%|
| 2 | 2300| 534| 2834|80.4%|
| 3 | 218| 17| 235|6.7%|
| 4 | 200| 23| 223|6.3%|
| 5 | 24| 2| 26|0.7%|
| 6 | 41| 3| 44|1.2%|
| 7 | 14| 0| 14|0.4%|
| 8 | 6| 2| 8|0.2%|
| 9 | 8| 0| 8|0.2%|
|10 | 17| 0| 17|0.5%|
|11 | 2| 0| 2|0.1%|
|12 | 2| 0| 2|0.1%|
Here is the PIe chart
I know that a new constant name "Tau" is proposed (#4897, #17496). But notice: "2pi" and "Tau" have the same number of characters. Then, it is obvious that familiarity is better. In fact, `2 * Math::PI` is 4 times more than `Math::PI * 2`, indicating that all programmers are copying "2pi" in their textbook.
The idea of 2pi came up regularly in chats among committers. The discussion quickly shifted to its generalization: should we treat `3e` as `3 * Math::E`, or even `42foo` as `42 * foo`? However, I noticed such a generalization is unnecessary because all we need is 2pi. Unneeded generalization is evil.
Here is a patch.
```diff
diff --git a/parse.y b/parse.y
index 55619273b8..93b16a16ac 100644
--- a/parse.y
+++ b/parse.y
@@ -10208,6 +10208,13 @@ parse_numeric(struct parser_params *p, int c)
return set_number_literal(p, tINTEGER, suffix, 10, 0);
}
}
+ else if (c == '2' && peek(p, 'p') && peek_n(p, 'i', 1)) {
+ tokadd(p, c);
+ tokadd(p, nextc(p));
+ tokadd(p, nextc(p));
+ tokfix(p);
+ return set_number_literal(p, tFLOAT, 0, 0, 0);
+ }
for (;;) {
switch (c) {
diff --git a/ruby_parser.c b/ruby_parser.c
index 6d85a72c5b..3a6e0b5704 100644
--- a/ruby_parser.c
+++ b/ruby_parser.c
@@ -936,6 +936,9 @@ VALUE
rb_node_float_literal_val(const NODE *n)
{
const rb_node_float_t *node = RNODE_FLOAT(n);
+ if (strcmp(node->val, "2pi") == 0) {
+ return DBL2NUM(2 * M_PI);
+ }
double d = strtod(node->val, 0);
if (node->minus) {
d = -d;
P I
Happy a r l fool
```
[1] I used these queries: [`/[^.]\b2 ?\* ?Math::PI/ language:Ruby`](https://github.com/search?type=code&q=%2F%5B%5E.%5D%5Cb2+%3F%5C*+%3FMath%3A%3API%2F+language%3ARuby) and [`/Math::PI *\* *2\b *[^.\/]/ language:Ruby`](https://github.com/search?type=code&q=%2FMath%3A%3API+*%5C*+*2%5Cb+*%5B%5E.%5C%2F%5D%2F+language%3ARuby)
--
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