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- Current State of Exceptions in Rakudo and Perl 6
- Meet DBIish, a Perl 6 Database Interface
- doc.perl6.org and p6doc
- Exceptions Grant Report for May 2012
- Exceptions Grant Report -- Final update
- Perl 6 Hackathon in Oslo: Be Prepared!
- Localization for Exception Messages
- News in the Rakudo 2012.05 release
- News in the Rakudo 2012.06 release
- Perl 6 Hackathon in Oslo: Report From The First Day
- Perl 6 Hackathon in Oslo: Report From The Second Day
- Quo Vadis Perl?
- Rakudo Hack: Dynamic Export Lists
- SQLite support for DBIish
- Stop The Rewrites!
- Upcoming Perl 6 Hackathon in Oslo, Norway
- A small regex optimization for NQP and Rakudo
- Pattern Matching and Unpacking
- Rakudo's Abstract Syntax Tree
- The REPL trick
- First day at YAPC::Europe 2013 in Kiev
- YAPC Europe 2013 Day 2
- YAPC Europe 2013 Day 3
- A shiny perl6.org site
- Creating an entry point for newcomers
- An offer for software developers: free IRC logging
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- Blackjack and Perl 6
- Why I commit Crud to the Perl 6 Test Suite
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- This Week's Contribution to Perl 6 Week 10: Implement samespace for Rakudo
- This Week's Contribution to Perl 6 Week 7: Implement try.rakudo.org
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- First Grant Report: Structured Error Messages
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- My first YAPC - YAPC::EU 2010 in Pisa
- Trying to implement new operators - failed
- Programming Languages Are Not Zero Sum
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- Notes from the YAPC::EU 2010 Rakudo hackathon
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- The Real World Strikes Back - or why you shouldn't forbid stuff just because you think it's wrong
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- Recent Perl 6 Developments August 2008
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- You are good enough!
Wed, 17 Nov 2010
The Real World Strikes Back - or why you shouldn't forbid stuff just because you think it's wrong
tl;dr;; version: arbitrary API limitations do more harm than good, even if meant well in the first place.
Most advanced libraries that help you with date calculations have separate data types for a point in time, and a time span. That's because those two concepts actually have different semantics. It doesn't make sense to add two points in time, but it does make sense to add two durations, or add a duration to a point in time.
In Perl 6, those two types are called
Duration. And obviously it makes sense to multiply a Duration
with a number, but it doesn't make sense to multiply two Durations, or take a
power of a Duration. Right?
That's when the real world struck back. Carl Mäsak did some timings, and then calculated averages and standard deviations. And for calculating standard deviations, you actually have to square those durations, add them up, and then calculate the square root.
So this perfectly legitimate use case shows that multiplication (and also
exponentiation) are perfectly fine operations on Durations. Likewise the
current specification disallows division of two Durations. Why? It's perfectly
fine to ask for the ratio of two time spans. How much longer (or shorter) are
my meetings with my current boss, compared to those with my previous boss?
That's the question that
Duration / Duration answers.
So, the real world taught me that putting restrictions on the allowed operations is a bad idea. It was meant well, it was supposed to catch operations that don't made sense to the designer, and presumably would catch some error that a confused beginner might make. But in the end it did more harm than good.
Duration class stores a number, and
re-dispatches all operations to that number, forbidding some of them. Having
learned my lesson, I suggest we get rid of it, and have
Instant return that number straight away. If some day we want to
add functionality to
Duration, we can still create that class as
a subclass of the number.