17 Feb
2024
17 Feb
'24
7:04 p.m.
Hi
p(1 and 2 or 3 and 4)
1. how many brackets do we need?
2. in my opinion the result should be 2, not 4.
What do you think?
Andreas
17 Feb
17 Feb
7:15 p.m.
New subject: [ruby-talk:444419] Re: logic in Ruby
There are orders of precedence at work here, but also some subtle ones that might not be
clear.
`and` and `&&` have different precedence. Likewise `or` and `||`.
And I cannot count the number of times that I have tried to be all minimal and introduced
a logical error in my code. Only staring at it long enough made it clear to me that a
whole branch of my comparison was being ignored.
I personally tend to put lots more parentheses in than might strictly be needed, and I
treat them as if they were comments -- they explain visually what I am imagining the
grouping to be. And sometimes that turns out to be necessary in order for it work the way
I expect it to.
A good question to ask yourself: would this be clearer as two lines? What would those two
lines be?
Could you use `return foo if 1 and 2` to short-circuit it?
Not an answer, but maybe a way for you to interrogate the question from a different
angle.
Walter
On Feb 17, 2024, at 2:04 PM, Information via ruby-talk
<ruby-talk(a)ml.ruby-lang.org> wrote:
Hi
p(1 and 2 or 3 and 4)
1. how many brackets do we need?
2. in my opinion the result should be 2, not 4.
What do you think?
Andreas
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18 Feb
18 Feb
9:42 p.m.
New subject: [ruby-talk:444421] Re: logic in Ruby
In general, you should always use `||` and `&&`. Except for expressions
like follows:
system "false" or raise "False return value"
Note how you don't need any parentheses in this case, but you would if
you used `||` or `&&`. Think of `or` and `and` more like how you think
about `if` or `unless` (as in, all 4 are for control flow).
In fact, all `||`, `&&`, `or`, `and` under the hood work exactly the
same (except for the priority). It's rather that the verbose ones were
designed for the usecase I wrote about.
On Sat, 2024-02-17 at 20:04 +0100, Information via ruby-talk wrote:
Hi
p(1 and 2 or 3 and 4)
1. how many brackets do we need?
2. in my opinion the result should be 2, not 4.
What do you think?
Andreas
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19 Feb
19 Feb
10:22 a.m.
New subject: [ruby-talk:444422] Re: logic in Ruby
On Sun, Feb 18, 2024 at 3:05 AM Information via ruby-talk <
ruby-talk(a)ml.ruby-lang.org> wrote:
Hi
p(1 and 2 or 3 and 4)
1. how many brackets do we need?
none if you know the order :)
2. in my opinion the result should be 2, not 4.
What do you think?
1 and 2 or 3 and 4
=> 4
evaluation left to right
1 && 2 || 3 && 4
=> 2
evaluation 1st: 1 && 2 => 2
evaluation 2nd: 3 && 4 => 4
evaluation last: 2 || 4 => 2
"or" and "and" have same priority.
"&&" precedes "||".
check: https://docs.ruby-lang.org/en/master/syntax/precedence_rdoc.html
kind regards --botp
Andreas
24 Feb
24 Feb
11:22 a.m.
New subject: [ruby-talk:444427] Re: logic in Ruby
Am 19.02.24 um 11:22 schrieb botp:
On Sun, Feb 18, 2024 at 3:05 AM Information via ruby-talk
<ruby-talk(a)ml.ruby-lang.org <mailto:ruby-talk@ml.ruby-lang.org>> wrote:
Hi
p(1 and 2 or 3 and 4)
1. how many brackets do we need?
none if you know the order :)
Maybe there is a misunderstanding:
p(--"--) doesnt work at all (Syntax error)
p((--"--) does the job. (Maybe for this the subject was misleading_
2. in my opinion the result should be 2, not 4.
What do you think?
So why should be there another result if using and/or instead of &&/|| ?
(1 and 2 or 3 and 4) != (1 && 2 || 3 && 4)
- That shouldn't be the case!
Andreas
1 and 2 or 3 and 4
=> 4
evaluation left to right
1 && 2 || 3 && 4
=> 2
evaluation 1st: 1 && 2 => 2
evaluation 2nd: 3 && 4 => 4
evaluation last: 2 || 4 
9:24 p.m.
New subject: [ruby-talk:444428] Re: logic in Ruby
Unlike Python, the "word" operators in Ruby aren't logic operators,
they're
flow control. They way they work is basically a carry-over from the way
that Perl handled them. They serve different purposes, and are not
equivalent.
On Sat, Feb 24, 2024, 03:24 Information via ruby-talk <
ruby-talk(a)ml.ruby-lang.org> wrote:
Am 19.02.24 um 11:22 schrieb botp:
On Sun, Feb 18, 2024 at 3:05 AM Information via ruby-talk <
ruby-talk(a)ml.ruby-lang.org> wrote:
Hi
p(1 and 2 or 3 and 4)
1. how many brackets do we need?
none if you know the order :)
Maybe there is a misunderstanding:
p(--"--) doesnt work at all (Syntax error)
p((--"--) does the job. (Maybe for this the subject was misleading_
2. in my opinion the result should be 2, not 4.
What do you think?
1 and 2 or 3 and 4
=> 4
evaluation left to right
1 && 2 || 3 && 4
=> 2
evaluation 1st: 1 && 2 => 2
evaluation 2nd: 3 && 4 => 4
evaluation last: 2 || 4
So why should be there another result if using and/or instead of &&/|| ?
(1 and 2 or 3 and 4) != (1 && 2 || 3 && 4)
- That shouldn't be the case!
Andreas
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25 Feb
25 Feb
12:10 a.m.
New subject: [ruby-talk:444430] Re: logic in Ruby
On Sat, Feb 24, 2024, at 6:22 AM, Information via ruby-talk wrote:
So why should be there another result if using and/or
instead of &&/||?
https://www.prestonlee.com/2010/08/04/ruby-on-the-perl-origins-of-and-versu…
(1 and 2 or 3 and 4) != (1 && 2 || 3
&& 4)
- That shouldn't be the case!
Perhaps not. I don't know why matz gave the "and"/"or" keywords
the same
precedence rather than making "and" higher precedence than "or", but
that's
been the case in ruby forever.
Perhaps it was a mistake since perl does maintain the relative precedence:
$ perl -e 'print(1 && 2 || 3 && 4);'
2
$ perl -e 'print(1 and 2 or 3 and 4);'
2
Or, perhaps matz felt that since the keyword form is intended for flow-control,
the flat precedence was appropriate.
$ git log -p parse.y
[...]
commit 3db12e8b236ac8f88db8eb4690d10e4a3b8dbcd4 (tag: v1_0_r2)
Author: matz <matz@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Fri Jan 16 12:13:05 1998 +0000
Initial revision
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@2
b2dd03c8-39d4-4d8f-98ff-823fe69b080e
diff --git a/parse.y b/parse.y
new file mode 100644
index 0000000000..02ff720bb3
--- /dev/null
+++ b/parse.y
@@ -0,0 +1,3717 @@
+/************************************************
+
+ parse.y -
+
+ $Author$
+ $Date$
+ created at: Fri May 28 18:02:42 JST 1993
+
+ Copyright (C) 1993-1996 Yukihiro Matsumoto
+
+************************************************/
[...]
+%left OR AND
[...]
+%left OROP
+%left ANDOP
[...]
12:54 a.m.
New subject: [ruby-talk:444431] Re: logic in Ruby
On Feb 19, 2024, at 02:22, botp via ruby-talk
<ruby-talk(a)ml.ruby-lang.org> wrote:
not quite. the LHS isn't evaluated:
#>>> 1 && 2 || raise("NO!") && 4
# => 2
1 and 2 or 3 and 4
=> 4
evaluation left to right
1 && 2 || 3 && 4
=> 2
evaluation 1st: 1 && 2 => 2
evaluation 2nd: 3 && 4 => 4
evaluation last: 2 || 4 => 2 "or" and "and" have same
priority.
"&&" precedes "||".
put another way, slightly more visual:
% rake debug R="1 && 2 || 3 &&
4"
s(:or,
s(:and, s(:lit, 1), s(:lit, 2)),
s(:and, s(:lit, 3), s(:lit, 4)))
which is what everyone expects, versus:
% rake debug R="1 and 2 or 3 and 4"
s(:and,
s(:or,
s(:and, s(:lit, 1), s(:lit, 2)),
s(:lit, 3)),
s(:lit, 4))
which is the same as:
% rake debug R="((1 and 2) or 3) and 4"
s(:and,
s(:or,
s(:and, s(:lit, 1), s(:lit, 2)),
s(:lit, 3)),
s(:lit, 4))
76
days inactive
84
days old
7 comments
7 participants
participants (7)
-
botp -
Frank J. Cameron -
hmdne -
Information -
James Pacheco -
Ryan Davis -
Walter Lee Davis