> Bryan R Harris wrote:
>>
>>> Bryan R Harris wrote:
>>>> This is unintuitive:
>>>>
>>>> perl -e 'print "> "; while(<>) {print(( eval $_ )[-1], "\n> ")}'
>>>>
>>>> ... then enter 2*012. It prints "20". 2*12 is obviously 24, but perl's
>>>> interpreting that "012" as octal. We sometimes have our numbers zero
>>>> padded
>>>> to make the columns line up, they're not octal.
>>>>
>>>> Is there any way to keep perl's eval from interpreting numbers starting
>>>> with
>>>> "0" as octal?
>>>>
>>>> I tried to regex them out but that regex is tricky since I'm writing a
>>>> custom calculator, and I have no idea what the user might enter.
>>> $ perl -lne 'BEGIN{$\="\n> ";print}s/(\d+)/0+$1/eg;print+(eval)[-1]'
>>>
>>>> 2*012
>>> 24
>>
>>
>> % perl -lne 'BEGIN{$\="\n> ";print}s/(\d+)/0+$1/eg;print+(eval)[-1]'
>>
>>> 2*012
>> 24
>>> 2*12.02
>> 24.4
>
> perl -lne 'BEGIN{$\="\n> ";print}s/(-?[\d.]+)/0+$1/eg;print+(eval)[-1]'
That's closer.
> 2*12.002.08
24.004
... where it probably ought to give a syntax error. (I wish it would just
let me inhibit the interpretation as octal.) I'll probably replace the
parenthesized section of the regex with ($float) where:
$float = qr/[+-]?\d*\.?\d+(?:e[+-]?\d+)?/;
>> Oops, not perfect, but I have a feeling the answer is going to look
>> something like that.
>>
>> "print+(eval)[-1]"??? What's the "+" for? You're amazing, John.
>
> The "+" is so that you don't get a syntax error because "print(eval)"
> with "[-1]" after it is nonsensical. BTW, why are you using a list
> slice anyway? Won't "print eval" work just as well?
>
> perl -lne 'BEGIN{$\="\n> ";print}s/(-?[\d.]+)/0+$1/eg;print eval'
That explains what it does, but not how it does it. Is there a perldoc that
discusses it? (As I've mentioned before, I can't hardly find anything in
perldoc without someone pointing me to it, though I am certainly grateful
for all the work people have done on it.) I do remember reading something
by Damian Conway that "+" evaluates to a space outside of mathematical
expressions, or something like that?
- Bryan
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