in reply to Re: A C-like brain in a Perl-like world
in thread A C-like brain in a Perl-like world

In perl everything is true except for:

0 (including the string equvalents "0" "0.0" etc which all evaluate to zero)

Sorry, tachyon, but that's not quite right. "0.0" is not false in perl:

% perl -le 'print "" ? "True" : "False"'
False
% perl -le 'print "0" ? "True" : "False"'
False
% perl -le 'print "0.0" ? "True" : "False"'
True

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Now with new grammatical goodness! (Thanks, blakem. ;-)

His Royal Cheeziness

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Re: Re: Re: A C-like brain in a Perl-like world
by ton (Friar) on Sep 27, 2001 at 05:31 UTC
    Apparently Perl is not as seemless in its conversions between strings and floating point numbers as it is in its conversions between strings and integers. Because the following works:

    % perl -le '$foo=0.0; print $foo ? "True" : "False";'
False

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    but the following does not: 
    % perl -le '$foo="0.0"; print $foo ? "True" : "False";'
True

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    -----
    Be bloody, bold, and resolute; laugh to scorn
    The power of man...
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      Perl seems to be assuming that "0.0" is a string, which is fair enough, if that is by design, which I assume it is. "return 0.0" would from a subroutine would evaluate as false.

      Perl will convert "0.0" to a number as soon as you do anything mathematical on it. Such as: 
      perl -e '$foo = "0.0" + 0; print $foo ? "True" : "False"'

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      Which behaves as you'd expect. This reminds me of (even though it's completely different):
      perl -e 'print "I cannot add" unless 19.08 + 2.01 == 21.09'

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      If I remember correctly this comes from an early TPJ article.

      Update: removed ' from print statement - thanks tilly - That's me in hybrid Win32 cmd.exe, Linux shell quoting mode :)

      Simon Flack ($code or die)
      $,=reverse'"ro_';s,$,\$,;s,$,lc ref sub{},e;$,
      =~y'_"' ';eval"die";print $_,lc substr$@,0,3;
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        You need to do one of the following to make that work: 
        perl -e 'print "I cannot add" unless 19.08 + 2.01 == 21.09'
perl -e 'print "I can'\''t add" unless 19.08 + 2.01 == 21.09'

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        BTW as Re: Strange (rounding?) problem points out, Perl often handles floats better if you use eq instead of == for testing equality...
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Re: Re: Re: A C-like brain in a Perl-like world
by tachyon (Chancellor) on Sep 27, 2001 at 15:16 UTC

    Hey good point! "0.0" is only zero if you force an eval on it one way or another. These are interesting: 

    print "0.0 is == 0\n" if "0.0" == 0;
$string_zero = "0.0";
print "True" if $string_zero;
print "True" if eval $string_zero;

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    cheers

    tachyon

    s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

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