in reply to strange arithmetic

I haven't found a direct answer for this (yet), (see Update below) but it's interesting that if you assign the math to another variable first, then print that variable, the number is printed correctly; for example:

$i = 2;
$j = (1-1/2000)**$i;
print $j;

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The output is:

0.99900025

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It seems that the print function is interpreting the number differently due to the parens. If you input a similar math problem directly into print, but without parens, the number comes out right.

$i = 2;
print 0.9995**$i;

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Output:

0.99900025

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Update: print is only printing what is in the parens because it is treating that part like the complete input to a function, ignoring the exponent part. Adding the blank string in front changes print to list operator mode, printing the entire answer.

To summarize: the two modes of print are:

# function mode
print (your code here);

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And

# list mode
print arg1, arg2, etc; # and/or the . operator

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--Nick

Replies are listed 'Best First'.
Re^2: strange arithmetic
by AnomalousMonk (Archbishop) on Jan 09, 2015 at 21:23 UTC
    ... print is only printing what is in the parens because it is treating that part like the complete input to a function ...

    Deparsing with full parenthesization (see O, B::Deparse) shows this clearly. (Note, in addition to "print (...) interpreted as function...", the warning about the return value of print being raised to an exponent and then thrown away!) 

    c:\@Work\Perl\monks>perl -wMstrict -MO=Deparse,-p -le
"my $i = 5;
 print (1-1/2000)**$i;
 print '' . (1-1/2000)**$i;
"
print (...) interpreted as function at -e line 1.
Useless use of exponentiation (**) in void context at -e line 1.
BEGIN { $^W = 1; }
BEGIN { $/ = "\n"; $\ = "\n"; }
use strict 'refs';
(my $i = 5);
(print(0.9995) ** $i);
print(('' . (0.9995 ** $i)));
-e syntax OK

c:\@Work\Perl\monks>perl -wMstrict -le
"my $i = 5;
 print (1-1/2000)**$i;
 print '' . (1-1/2000)**$i;
"
print (...) interpreted as function at -e line 1.
Useless use of exponentiation (**) in void context at -e line 1.
0.9995
0.997502498750313

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