When should one use "and" and "or"

Ruby
1

Hi All,

just got hit w the ff

case
when x==1 or x==2
print “yeoh!”
end
SyntaxError: compile error
(irb):17: syntax error, unexpected kOR, expecting kTHEN or ‘:’ or ‘\n’
or ‘;’
when x==1 or x==2
^

“or” and “and” both exhibit the behaviour in ruby1.8/1.9.

workaround
1 put parens around the condition (not again)
2 replace or/and with ||/&&

i believe there are other similar quirks when using “and/or”…
has ruby relegated the use of “and/or”…?

best regards -botp

2

On Feb 4, 9:55 pm, botp [email protected] wrote:

Hi All,

just got hit w the ff

case
when x==1 or x==2
print “yeoh!”
end

x = 5
==>5
case x
when 2,3
p ‘no’
when 4,5
p ‘yes’
end
“yes”
==>nil

3

botp wrote:

i believe there are other similar quirks when using “and/or”…
has ruby relegated the use of “and/or”…?

No, but it’s essentially inherited from perl. These operators have
extremely low precedence, so without parens your statement was being
parsed as something like

(when x==1) or x==2

I think the typical perl use is something like:

open F, “foo” or die “Oops”;

If you use || then you need extra params so you don’t get
open(F, “foo” || die “Oops”);

But if you rely on poetry mode like this it may still trip you up. IMO
you’re better off with:

a = (some-expr) || (raise “Oops”)
a = (some-expr) || raise(“Oops”)

4

On Fri, Feb 5, 2010 at 3:14 PM, Brian C. [email protected]
wrote:

No, but it’s essentially inherited from perl. These operators have
extremely low precedence, so without parens your statement was being
parsed as something like

(when x==1) or x==2

I think the typical perl use is something like:
…

but brian, i’m still inside the “case” block. can’t ruby sense that?

best regards -botp

5

On Fri, Feb 5, 2010 at 1:45 PM, w_a_x_man [email protected] wrote:
#> x = 5
#> ==>5
#> case x
#> when 2,3
#> p ‘no’
#> when 4,5
#> p ‘yes’
#> end

of course i know that :wink:
im talking about the second type of “case”, eg

case
when x.baz and y.foo
…

best regards -botp

6

botp wrote:

but brian, i’m still inside the “case” block. can’t ruby sense that?
And shouldn’t ‘when’ have the same precedence as ‘if’?

At least for ‘or’, you can use a comma instead:

case
when x==1, x==2; puts “1 or 2”
end

but it doesn’t read as well, and there’s nothing that works like this
for ‘and’.

7

botp wrote:

�(when x==1) or x==2

I think the typical perl use is something like:
…

but brian, i’m still inside the “case” block. can’t ruby sense that?

I agree, but in the absence of a formal grammar you’ll have to look at
the implementation.