felher

starting A
^Cstarting B
stopping B
stopping A

felher

The Mysterious Case of The Missing flatMap

When you're starting to use functional programming libraries in scala there is something which might not feel right to you. But you suppress that feeling because everything seems to work just a fine. You try to move on, but a question is racing through your head. I'm talking of course about:

Why the hell can I call flatMap and map on my data types, even though it isn't implemented on my data types?

Consider a small example. We will write our own mirror of the Option data type. The original Option has two cases, Some(a) if there is a value and None if there is none. Let's call our data type Maybe which the cases Just(a) and Empty.

sealed trait Maybe[+A]

felher

I keep some of my config files in a git repository.
I have multiple machines and on some machines I have to
change some parts of the config file, while keeping the
other parts unchangend and up to date.
I created branches for the different machines and merged
the main branch back into the machine branches, which
makes it look like that:
Maschine1:   o-o-o-o-o...
            / / / / /
Master:    o-o-o-o-o-...

felher

use v6;

constant %ah = (^10).categorize: *%3;

say %ah.perl;

felher

grammar Rules {
	token TOP                                       { <line>*                                                }
	token    line                                   { <empty-line> | <field-specification-line> | <tag-line> }
	token        empty-line                         { [ '#' \V* ]? \v                                        }
	token        field-specification-line           { '!' <field-name> \v                                    }
	token                                field-name { 'to' | 'from' | 'subject'                              }
	token        tag-line                           { <tag-command> \h+ <conjunction>+ % [\h* '|' \h*] \v    }
	token                tag-command                { <sign> <tag-name>                                      }
	token                           sign            { ['+' | '-']                                            }
	token                           tag-name        { <alnum>+                                               }

felher

X und Y sind zwei verschiedene ganzzahlen, groesser als  1, deren Summe kleiner 100 ist. S und P sind zwei matehmatiker;
S kennt sie Summe X+Y, P kennt das Produkt X*Y, und beide kennen die Informationen in diesen Saetzen.
Dann passiert die folgende Unterhaltung:

P sagt "Ich kann die Zahlen nicht finden."
S sagt "Ich war mir sicher, dass du die Zahlen nicht finden konntest. Ich kann sie auch nicht finden."
P sagt "Dann habe ich diese Zahlen gefunden."
S sagt "Wenn du sie gefunden hast, dann hab ich sie auch gefunden."

Um welche zwei Zahlen handelt es sich?

felher

type MT = (Int, Int)
 
allTuples :: [MT]
allTuples = [ (x, y) | x <- [2 .. 97], y <- [2 .. 97], x >= y, x + y < 100]
 
isPrime :: Int -> Bool
isPrime x = null [d | d <- [2 .. x - 1], x `rem` d == 0]
 
primeTuples :: [MT]
primeTuples = filter isPrimeTuple allTuples where

felher

# we use the [] reduction meta operator along with the Cartesian Product
# operator X to create the Cartesian Product of four times [1..9] and then get
# all the elements where the number of unique digits is four.
my @candidates = ([X] [1..9] xx 4).tree.grep: *.uniq == 4;

repeat {
	my $guess = @candidates.pick;
	my ($bulls, $cows) = read-score;
	@candidates .= grep: &score-correct;

felher

multi sub a(Int $x) { ... };
multi sub a('list', *@array) { ... };
&a.candidates_matching();

felher

From 6beffa8d2f4b18fcabd0c83a93310bc70a122ea3 Mon Sep 17 00:00:00 2001
From: Felix Herrmann <felix@herrmann-koenigsberg.de>
Date: Thu, 2 Aug 2012 20:07:03 +0200
Subject: [PATCH] [Temporal] change constructor of Date to use default values
 for year/month/day

---
 src/core/Temporal.pm |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)