Issue #20404 has been reported by mame (Yusuke Endoh). ---------------------------------------- Feature #20404: `2pi` https://bugs.ruby-lang.org/issues/20404 * Author: mame (Yusuke Endoh) * Status: Open ---------------------------------------- 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) -- https://bugs.ruby-lang.org/