Peter Babnik Coding

M
XMAS LECTURE
2013
Vocals: Anya Bagge and Sarah Piller
Piano: Peter Babnik
Coding: Ralf Lämmel
BEAUTIFUL CODE
LAST CHRISTMAS — WHAM!
http://en.wikipedia.org/wiki/Last_Christmas
http://german.about.com/library/blmus_morgenkommt.htm
MORGEN KOMMT DER
WEIHNACHTSMANN
!
DEUTSCH
TEXT: Hoffmann von Fallersleben
(1850)
!
Morgen kommt der Weihnachtsmann,
Kommt mit seinen Gaben.
Trommel, Pfeifen und Gewehr,
Fahn und Säbel und noch mehr,
Ja ein ganzes Kriegesheer,
Möcht' ich gerne haben.
!
!
!
!
Bring' uns, lieber Weihnachtsmann,
Bring' auch morgen, bringe
Musketier und Grenadier,
Zottelbär und Panthertier,
Roß und Esel, Schaf und Stier,
Lauter schöne Dinge!
!
Doch du weißt ja unsern Wunsch,
Kennst ja unsre Herzen.
Kinder, Vater und Mama
Auch sogar der Großpapa,
Alle, alle sind wir da,
Warten dein mit Schmerzen.
http://de.wikipedia.org/wiki/Morgen_kommt_der_Weihnachtsmann
MOZART: !
"MORGEN KOMMT DER WEIHNACHTSMANN"
AUSWAHL VON VARIATIONEN
LESS BEAUTIFUL CODE
class HelloWorld {
static public void main( String args[] ) {
System.out.println( "Hello World!" );
}
}
Java
MORE BEAUTIFUL CODE
print "Hello World!”
Python
BOOKS YOU ABSOLUTELY SHOULD READ
Jing
le B
ells
1/3
http://www.carols.org.uk/jingle_bells.htm
Dashing through the snow
In a one horse open sleigh
O'er the fields we go
Laughing all the way
Bells on bob tails ring
Making spirits bright
What fun it is to laugh and sing
A sleighing song tonight
!
Jing
le B
ells
2/3
!
Oh, jingle bells, jingle bells
Jingle all the way
Oh, what fun it is to ride
In a one horse open sleigh
Jingle bells, jingle bells
Jingle all the way
Oh, what fun it is to ride
In a one horse open sleigh
!
A day or two ago
I thought I'd take a ride
And soon Miss Fanny Bright
Was seated by my side
The horse was lean and lank
Misfortune seemed his lot
We got into a drifted bank
And then we got upsot
!
Jing
le B
ells
3/3
!
Oh, jingle bells, jingle bells
Jingle all the way
Oh, what fun it is to ride
In a one horse open sleigh
Jingle bells, jingle bells
Jingle all the way
Oh, what fun it is to ride
In a one horse open sleigh yeah
!
Jingle bells, jingle bells
Jingle all the way
Oh, what fun it is to ride
In a one horse open sleigh
Jingle bells, jingle bells
Jingle all the way
Oh, what fun it is to ride
In a one horse open sleigh
Chapter 1 of Beautiful code:
A Regular Expression Matcher
Brian Kernighan
REGULAR EXPRESSION CHARACTERS
•
Character
Meaning
•
c
matches any literal character c
•
.
matches any single character
•
^
matches the beginning the input string
•
$
matches the end of the input string
•
*
matches zero or more occurrences of the previous character
EXAMPLES
re1 = "xm.ss*"
re2 = “^xm.ss*”
!
match(re1, “xmas”) match(re2, “xmas") match(re1, "xmaz") match(re2, "xmaz") match(re1, "qxmas")
match(re2, "qxmas")
match(re1, “xmess")
match(re2, “xmess")
▶︎ 1
▶︎ 1
▶︎ 0
▶︎ 0
▶︎ 1
▶︎ 0
▶︎ 1
▶︎ 1
int match(char *re, char *text)
{
if (re[0] == '^')
return matchhere(re+1, text);
do { /* must look at empty string */
if (matchhere(re, text))
return 1;
} while (*text++ != '\0');
return 0;
}
int matchhere(char *re, char *text)
{
if (re[0] == '\0')
return 1;
if (re[1] == '*')
return matchstar(re[0], re+2, text);
if (re[0] == '$' && re[1] == '\0')
return *text == '\0';
if (*text!='\0' && (re[0]=='.' || re[0]==*text))
return matchhere(re+1, text+1);
return 0;
}
int matchstar(int c, char *re, char *text)
{
do { /* a * matches zero or more instances */
if (matchhere(re, text))
return 1;
} while (*text!='\0' && (*text++==c || c=='.'));
return 0;
}
.C
/* match: search for re anywhere in text */
/* matchhere: search for re at beginning of text */
/* matchstar: search for c*re at beginning of text */
.C
/* match: search for re anywhere in text */
int match(char *re, char *text)
{
if (re[0] == '^')
return matchhere(re+1, text);
do { /* must look at empty string */
if (matchhere(re, text))
return 1;
} while (*text++ != '\0');
return 0;
}
.C
/* matchhere: search for re at beginning of text */
int matchhere(char *re, char *text)
{
if (re[0] == '\0')
return 1;
if (re[1] == '*')
return matchstar(re[0], re+2, text);
if (re[0] == '$' && re[1] == '\0')
return *text == '\0';
if (*text!='\0' && (re[0]=='.' || re[0]==*text))
return matchhere(re+1, text+1);
return 0;
}
.C
/* matchstar: search for c*re at beginning of text */
int matchstar(int c, char *re, char *text)
{
do { /* a * matches zero or more instances */
if (matchhere(re, text))
return 1;
} while (*text!='\0' && (*text++==c || c=='.'));
return 0;
}
http://www.carols.org.uk/white_christmas.htm
WHITE CHRISTMAS
I'm dreaming of a white Christmas Just like the ones I used to know Where the treetops glisten, and children listen To hear sleigh bells in the snow
!
I'm dreaming of a white Christmas With every Christmas card I write May your days be merry and bright And may all your Christmases be
white !
I'm dreaming of a white Christmas With every Christmas card I write May your days be merry and bright And may all your Christmases be
white
.hs
match :: String -> String -> Bool
match ('^':r) = matchHere r
match r
= or . map (matchHere r) . tails
matchHere :: String -> String -> Bool
matchHere (c:'*':r) xs = matchStar c r xs
matchHere "$"
xs = null xs
matchHere (r:rs) (x:xs) = (r == '.' || r == x) && matchHere rs xs
matchHere r
_
= null r
matchStar :: Char -> String -> String -> Bool
matchStar _ r xs | matchHere r xs = True
matchStar c r (x:xs) = (c == '.' || c == x) && matchStar c r xs
matchStar _ _ _
= False
© Remco Niemeijer
.pro
match(['^'|Rs], T) :- matchHere(Rs, T).
match(R, T)
:- matchHere(R, T).
match(R, [_|Ts])
:- matchHere(R, Ts).
!
matchHere([], _).
matchHere(['$'], []).
matchHere([R,'*'|Rs], T)
:- matchStar(R, Rs, T).
matchHere([R|Rs], [R|Ts])
:- matchHere(Rs, Ts).
matchHere(['.'|Rs], [_|Ts]) :- matchHere(Rs, Ts).
!
matchStar(_, Rs, Ts)
matchStar(R, Rs, [R|Ts])
matchStar('.', Rs, [_|Ts])
matchStar(R, Rs, [R|Ts])
matchStar('.', Rs, [_|Ts])
:::::-
matchHere(Rs, Ts).
matchHere(Rs, Ts).
matchHere(Rs, Ts).
matchStar(R, Rs, Ts).
matchStar('.', Rs, Ts).
© Guillermo Oscar «Tordek» Freschi
http://www.carols.org.uk/let_it_snow.htm
LET IT SNOW
Oh the weather outside is frightful, But the fire is so delightful,
And since we've no place to go,
Let It Snow! Let It Snow! Let It Snow!
!
It doesn't show signs of stopping,
And I've bought some corn for popping,
The lights are turned way down low,
Let It Snow! Let It Snow! Let It Snow!
!
When we finally kiss goodnight,
How I'll hate going out in the storm!
But if you'll really hold me tight,
All the way home I'll be warm.
!
The fire is slowly dying,
And, my dear, we're still good-bying,
But as long as you love me so,
Let It Snow! Let It Snow! Let It Snow!
Chapter 23 of Beautiful code:
Distributed programming with MapReduce
Jeffrey Dean and Sanjay Ghemawat
COUNT WORDS
map<string, int> word_count;
for each document d for each word w in d
word_count[w]++;
… save word_count to persistent storage …
PARALLELIZED COUNT WORDS
struct CountTable {
Mutex lock;
map<string, int> word_count;
}
const int kNumBuckets = 256;
CountTable tables[kNumBuckets];
for each document d in parallel
for each word w in d {
int bucket = hash(w) % kNumBuckets;
tables[bucket].lock.Lock();
tables[bucket].word_count[w]++;
tables[bucket].lock.Unlock();
}
for (int b=0; b<kNumBuckets; b++)
… save tables[b].word_count to persistent storage …
tm
duf
roe
.h
uri.
de/
o
htt du
p://
f
ww röhl
w.n ich
ana e
mo
usk
o
Oh
O du fröhliche
O du selige
Gnadenbringende Weihnachtszeit
Welt ging verloren
Christ ist geboren
Freue, freue dich, o Christenheit
!
O du fröhliche
O du selige
Gnadenbringende Weihnachtszeit
Christ ist erschienen
Uns zu versühnen
Freue, freue dich, o Christenheit
!
O du fröhliche
O du selige
Gnadenbringende Weihnachtszeit
Himmlische Heere
Jauchzen Dir Ehre
Freue, freue dich, o Christenheit
MAPPERS AND REDUCERS
Input data
Intermediate data
Output data
k1 v1
partition 1
k2 [v2]
piece 1
k2 v3
reduce 1
map 1
partition R
partition 1
map M
piece M
partition R
reduce R
INPUT & OUTPUT PROCESSORS
const int M = 1000; // Number of input processors
const int R = 256; // Number of output processors
main() {
// Number of documents to assign to each process
const int D = number of documents / M;
for (int i=0; i<M; i++)
fork InputProcess(i*D, (i+1)*D);
for (int i=0; i<R; i++)
fork OutputProcess(i);
… wait for all processors to finish …
INPUT PROCESSORS
void InputProcess(int start_doc, int end_doc) {
map<string, int> word_count[R]; // table per output process
for each document d in range [start_doc .. end_doc-1]
for each word in d {
int b = hash(w) % R;
word_count[b][w]++;
}
for (int b=0; b<R; b++) {
string s = EncodeTable(word_count[b]);
… send s to output process b …
}
}
OUTPUT PROCESSORS
void OutputProcess(int bucket) {
map<string, int> word_count;
for each input process p {
string s = … read message from p …
map<string, int> partial = DecodeTable(s);
for each <word, count> in partial do
word_count[word] += count;
}
… save word_count to persistent storage …
}
DIVISION INTO MAP AND REDUCE
void Map(string document) {
for each word w in document
EmitIntermediate(w, “1’);
}
!
void Reduce(string word, list<string> values) {
int count = 0;
for each v in values
count += StringToInt(v):
Emit(word, IntToString(count));
}
DRIVER FOR MAP AND REDUCE
map<string, list<string>> intermediate_data;
void EmitIntermediate(string key, string value) {
intermediate_data[key].append(value);
}
void Emit(string key, string value) {
… write key/value to final data file …
}
void Driver(MapFunction mapper, ReduceFunction reducer) {
for each input item do {
mapper(item);
}
for each key k in intermediate_data {
reducer(k, intermediate_data[k]);
}
}
TIE THE KNOT
main() {
Driver(Map, Reduce);
}
http://www.stlyrics.com/lyrics/elf/santaclausiscomingtotown.htm
SANTA CLAUS IS COMING TO TOWN
You better watch out
You better not cry
Better not pout
I'm telling you why
Santa Claus is coming to town
He's making a list
And checking it twice;
Gonna find out Who's naughty and nice
!
!
!
!
Santa Claus is coming to town
He sees you when you're sleeping
He knows when you're awake
He knows if you've been bad or good
So be good for goodness sake!
O! You better watch out!
You better not cry
Better not pout
I'm telling you why
Santa Claus is coming to town
Santa Claus is coming to town
Chapter 24 of Beautiful code:
Beautiful Concurrency
Simon Peyton Jones
BANK TRANSFER PROBLEM
Write a procedure to transfer from one bank account to
another. To keep things simple, both accounts are held in
memory; no interaction with databases is required. The
procedure must operate correctly in a concurrent program, in
which many threads may call transfer simultaneously. No thread
should be able to observe a state in which the money has left
one account, but not arrived in the other (or vice versa).
A SIMPLE ACCOUNT CLASS
class Account {
int balance;
synchronized void withdraw(int n) {
balance = balance - n;
}
void deposit(int n) {
withdraw(-n);
}
}
FIRST ATTEMPT AT TRANSFER
void transfer(Account from, Account to, int amount) {
from.withdraw(amount);
to.deposit(amount);
}
EXPLICIT LOCKING CODE
void transfer(Account from, Account to, int amount) {
from.lock(); to.lock();
from.withdraw(amount);
to.deposit(amount);
from.unlock(); to.unlock();
}
ORDERED LOCKS
if from < to
then { from.lock(); to.lock(); }
else { to.lock(); from.lock(); }
LOCKS ARE BAD
•
Taking too few locks
•
Taking too many locks
•
Taking the wrong locks
•
Taking locks in the wrong order
•
Error recovery
•
Lost wakeups and erroneous retries
http://www.youtube.com/watch?v=4kkQJuQlc_Q
COLOURFUL XMAS
TRANSFER IN HASKELL
transfer :: Account -> Account -> Int-> IO ()
transfer from to amount = ...
SOFTWARE TRANSACTIONAL MEMORY IN HASKELL
transfer :: Account -> Account -> Int-> IO ()
transfer from to amount
= atomically (do { deposit to amount
; withdraw from amount })
Provided guarantees
of “atomically act”
•
Atomicity: The effects of execution become visible to
another thread all at once. This ensures that no thread
can see a state in which money has been deposited in to
but not yet withdrawn from from.
•
Isolation: During its execution, act is completely
unaffected by other threads. It is as if takes a snapshot of
the state of the world when it begins running, and then
executes against that snapshot.
TRANSACTION VARIABLES
type Account = TVar Int
!
withdraw :: Account -> Int -> STM ()
withdraw acc amount
= do { bal <- readTVar acc
; writeTVar acc (bal - amount) }
!
deposit :: Account -> Int -> STM ()
deposit acc amount = withdraw acc (- amount)
http://www.carols.org.uk/winter_wonderland.htm
WINTER WONDERLAND
Sleigh bells ring, are you listening, In the lane, snow is glistening
A beautiful sight,
We're happy tonight.
Walking in a winter wonderland.
!
Gone away is the bluebird,
Here to stay is a new bird
He sings a love song,
As we go along,
Walking in a winter wonderland.
!
In the meadow we can build a snowman,
Then pretend that he is Parson Brown
!
He'll say: Are you married?
We'll say: No man, But you can do the job
When you're in town.
!
Later on, we'll conspire,
As we dream by the fire
To face unafraid, The plans that we've made,
Walking in a winter wonderland.
!
In the meadow we can build a snowman,
And pretend that he's a circus clown
We'll have lots of fun with mister
snowman,
Until the other kids knock him down.
!
When it snows, ain't it thrilling,
Though your nose gets a chilling
We'll frolic and play, the Eskimo way,
Walking in a winter wonderland.
http Rud
://w
o
ww lph,
.car
ols.o the
r
rg.u
e
k/r u d n
o
dolf
_the sed
_red rei
_no nde
sed
e
_rei r
nde
er.h
tm
Rudolph, the red-nosed reindeer had a very shiny nose. And if you ever saw him, you would even say it glows.
!
All of the other reindeer used to laugh and call him names. They never let poor Rudolph join in any reindeer games. !
Then one foggy Christmas Eve Santa came to say: "Rudolph with your nose so bright, won't you guide my sleigh tonight?" !
Then all the reindeer loved him as they shouted out with glee, Rudolph the red-nosed reindeer, you'll go down in history!
http://www.carols.org.uk/we_wish_you_a_merry_christmas.htm
WE WISH YOU A MERRY CHRISTMAS
We wish you a Merry Christmas; We wish you a Merry Christmas; We wish you a Merry Christmas and a Happy New Year. Good tidings we bring to you and your kin; Good tidings for Christmas and a Happy New Year.
!
Oh, bring us a figgy pudding; Oh, bring us a figgy pudding; Oh, bring us a figgy pudding and a cup of good cheer
We won't go until we get some; We won't go until we get some; We won't go until we get some, so bring some out here
!
We wish you a Merry Christmas; We wish you a Merry Christmas; We wish you a Merry Christmas and a Happy New Year.
Wir wünschen Euch ein Frohes Fest
und Ein Gesundes Neues Jahr 2014.