I have turned the module over to Jenda Krynicky. Jenda has released version 0.68, which is also available from CPAN.
I may stop maintaining this web page.
Several months ago, Jenda Krynicky sent me some useful patches for Interpolation.pm. They support interpolators with multiple arguments, callable in a variety of convenient ways. Eventually, these will be in the new version. Until then, you can get a patched alpha version from Jenda's site.
Suppose your program needs to print out a lot of dollar amounts, and you'd like to print each one out with a leading dollar sign, commas every three places, and always two places for cents after a decimal point, so that the number 1234.5 should be formatted as $1,234.50. One way to do it is to define a commify routine to insert the punctuation (which you can crib from the FAQ) and do something like this:
$com_SALARY = commify($SALARY);
print "Last year I made $com_SALARY.\n";
That can get old pretty quick---you end up with a lot of useless variables like $com_SALARY cluttering up your program. Or you could use printf:
printf "Last year I made %s.\n", commify($SALARY);
This is all right, but a little hard to read, because you have to match up the formatting codes in the first argmuent with the values in the rest of the arguments.
The bottom line here is that `commify' is just cosmetic, for output formatting, not really an interesting or important part of the program, and you'd really like to sweep it under the rug and make it take up as little space as possible.
You can do that with Interpolation. Here's what that example looks like if you use Interpolation:
print "Last year I made $money{$SALARY}.\n";
One line, no extra variables, and no sign of the formatting except the descriptive word money there to say what the format is. If you're going to be doing a lot of money, and the word money is too long, you can use M instead:
print "Last year I made $M{$SALARY}.\n";
Or you can use whatever name you prefer, even _. If you're going to be printing out a lot of percentages to two decimal places, you might name the interpolator %, so that you could write this:
print "Sales have increased by $%{$increase}.\n";
And, since $% is an abbreviation for `format in a way appropriate for percentages', what it would print would look like this:
print "Sales have increased by 3.12%.\n";
You can have as many different formats as you want, and you can give them whatever names you want. You can install a formatter in one part of your program, and uninstall it again when you're done with it.
Here's another example: You do a database call and get back the name of a U.S. state or Canadian province. The database doesn't capitalize these consistently; sometimes they're correct, sometimes all uppercase, sometimes all lowercase. You need to capitalize correctly when you print out the results.
Rather than explicitly calling a capitalization function each and every time you get data from the database, you can use an interpolator, like this:
print "Database returned: $Cap{$RESULT}.\n";
$Cap is an interpolator that fixes the capitalization of anything it gets, in this case the contents of $RESULT.
The argument to an interpolator can be any Perl expression. In the context of the money example, that means you can do something like this:
print "If I get a 6% raise, I'll be making $money{$SALARY * 1.06}.\n";
And again you save on space and on useless temporary variables. It seems like this is prone to abuse, but in many cases, like this one, it does seem to make the code clearer, putting emphasis on the important parts and preventing a lot of excess verbiage that would obscure what was really going on.
As a special case, you can evaluate arbitrary expressions into strings, like this: "1 + 2 = $eval{1 + 2}", which turns into 1 + 2 = 3.
To join a mailing list about Interpolation, send a blank mail message to mjd-perl-interpolation-request@plover.com.
An old TIEARRAY feature left over from Identity.pm is now officially deprecated and raises a warning the first time it is used.
New sprintf1 builtin lets you write the call as $S{format,args} instead of $S{format}{args}.
This was the initial release.
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