Lecturecontent
TDDA69DataandProgramStructure
Introduction
CyrilleBerger
CourseIntroduction
IntroductiontothedifferentProgramming
Paradigm
Thedifferentprogrammingparadigms
Whydifferentparadigms?
IntroductiontoFunctionalProgramming
Expressions
Functions
Control
Recursion
Advantagesandinconvenientsoffunctional
programming
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Coursegoals
CourseIntroduction
Describeaspectsofevaluationand
executionindifferentlanguagemodels
Explainanddemonstratehowdesign
choicesaffecttheexpressivenessand
efficacyofaprogramminglanguage
Analyzeandvalueprogramminglanguages
basedontheirevaluationand
compilationstrategies
Implementprogramminglanguagesinthe
formofaninterpreterandacompiler
4
Programminglanguages
Whydoyouneedtoknowhowprogramareinterpreted?
Itwillhelpyouunderstandwhy
programminglanguageworksacertain
wayandwhatarethelimits
Newprogramminglanguagesand
interpretersareconstantlybeing
developed
Existinginterpretersareconstantly
beingdeveloped
Generalpurposes:C,C++,Java,Python...
Specialpurposes:Prolog,Matlab,R,
Agent0...
Scripting:JavaScript,VBA...
Historical:Fortran,Lisp...
toimproveperformance,security,addnewfeatures...
5
6
Howisaprograminterpreted?
Evolutionofprogramminglanguages
Sourcecode
Parser
Parser
7
AbstractSyntaxTree
Treevisitor
Generator
Sourcecode
Bytecode
VirtualMachine
Assembler
Assembly
...
OperatingSystem
CPU
8
Facebook'sworkonthePHPintepreter
WhydidFacebookneedtodeveloptheirownPHPinterpreter?
FacebookstartedwithPHPin2004
Backatthetime,PHPwas
thegoldstandardforwebsite
programmingandprototyping
Butthisiscausingproblemsand
forpracticalreasonsthey
cannotchangeprogramming
language
www.govote.at493985
start
9
WhatdidFacebookdo?
ThestandardPHPinterpreterisusing
avirtualmachine(Zend)
TheydevelopedatooltoconvertPHP
toC++
Thentheydevelopedanew
interpreterthatdoJust-In-Time
(JIT)compilation,calledHHVM
TheyintroducedHack,avariantofPHP
withatypingsystem
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10
Andotherexamples...
GooglewithJava,Dalvik,
PythonwithCPythonvs
Qt'sJavaScript,switchingfrom
ASTInterpretationtoJITandtoa
mixofJITandASTInterpretation
...
12
Listoflectures
Book(s)
StructureandInterpretationof
ComputerProgramsinPythonby
HalAbelson,JerrySussman,Julie
SussmanandJohnDenero
StructureandInterpretationof
ComputerProgramsbyHal
Abelson,JerrySussmanandJulie
Sussman
1IntroductionandFunctionalProgramming
2ImperativeProgrammingandDataStructures
3Parsing
4Evaluation
5ObjectOrientedProgrammingandtypessystem
6Macrosand
7VirtualMachinesandBytecode
8GarbageCollectionandNativeCode
9ConcurrentComputing
10DeclarativeProgramming
11Logic
12Summary
13
Listoflabs
14
Divisionoftime
1FunctionalProgramming
2Supportingclassforaninterpreter
3ECMAScriptInterpreter
4Macros
5Bytecode
6Garbagecollector
7SQpy
24hlectures(in12sessions)
40hlabs(in20sessions)
8htutorials(in4
88hhomework
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16
Lastyearevaluationandimprovments
Toomuchboilerplatting,Labsand
lecturesarenotwellconnected
Twonewlabs
Quizzesarenicebutteacherwaitfortoo
long
IntroductiontothedifferentProgrammingParadigm
Introduceatimeout
Teacherisshy,slidesaremostlyusedby
theteachertoknowwhattosay
Introducemoreinterractivity
Theexamisworthmorethantwocredits
17
Thedifferentprogrammingparadigms
20
Declarative
ProgrammingParadigm(2/2)
Expresseslogicofcomputation
withoutcontrolflow:
Imperative
declarative
functional
Symbolic
Whatshouldbecomputedandnothowit
shouldbecomputed.
Examples:XML/HTML,antlr4/yacc/
regularexpressions,make/ants,
SQL,...
Logic
Object-Oriented
21
Declarative-Examples
<b>Helloworld!</b>
SELECTnameFROMstudent
WHEREcourseeq'TDDA69'
grammarHello;
r:'hello'ID;
ID:[a-z]+;
WS:[''\t\r\n]+->skip;
22
Functional
Computationaretreated
asmathematicalfunction
withoutchanginganyinternalstate
Examples:Lisp,Scheme,
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24
Functional-Examples
Imperative
(print"HelloWorld")
(take25(squares-of
Expresshowcomputationare
executed
->(1491625364964...576625)
Describescomputationintermofstatements
thatchangetheinternalstate
Examples:C/C++,Pascal,
Java,Python,JavaScript...
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26
Object-Oriented
Imperative-Examples
Basedontheconceptofobjects,
whicharedatastructures
containingfieldsandmethods
for(vari=1;i<26;++i)
{
varsq=i*i;
console.log(sq)
}
#include<stdio.h>
intmain()
{
charch;
printf("Enteracharacter\n");
scanf("%c",&ch);
if(ch=='a'||ch=='A'||ch=='e'||ch=='E'||ch=='i'||ch=='I'||ch=='o'||
ch=='O'||ch=='u'||ch=='U')
printf("%cisavowel.\n",ch);
else
printf("%cisnotavowel.\n",ch);
return0;
}
Programsaredesignedbymakingobjects
interactwitheachothers
Examples:C++,Java,C#,
Python,Ruby,JavaScript...
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28
Othersparadigmlanguages
Object-Oriented-Programming
Logic
#include<iostream>
classCharacter:publicSymbol
{
public:
Character(char_c):m_c(_c){}
boolisVowel()const
{
returnch=='a'||ch=='A'||ch=='e'||ch=='E'||ch==
'i'
||ch=='I'||ch=='o'||ch=='O'||ch=='u'||ch=='U';
}
private:
charm_c;
};
intmain()
{
charc;
std::cout<<"Enteracharacter:\n";
std::cin>>c;
Characterch(c);
if(ch.isVowel())
{
std::cout<<c<<"isavowel.\n";
}else{
std::cout<<c<<"isnotavowel.\n";
}
}
BasedonFormallogic:expressingfactsand
rules
Symbolic
Aprogramcanmanipulateitsownformulas
andcomponentsasiftheyaredata
Example:prolog
29
Logicprogramming
likes(mary,food).
likes(mary,wine).
likes(john,wine).
likes(john,mary).
|?likes(mary,food).
yes.
|?-likes(john,wine).
yes.
|?-likes(john,food).
no.
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Symbolicprogramming
d(X,X,1):-!./*d(X)w.r.t.Xis1*/
d(C,X,0):-atomic(C)./*IfCisaconstant*/
/*thend(C)/dXis0*/
d(U+V,X,R):-/*d(U+V)/dX=A+Bwhere*/
d(U,X,A),/*A=d(U)/dXand*/
d(V,X,B),
R=A+B.
...
d(sin(W),X,Z*cos(W)):-/*d(sin(W))/dX=Z*cos(W)*/
d(W,X,Z)./*whereZ=d(W)/dX*/
d(exp(W),X,Z*exp(W)):-/*d(exp(W))/dX=Z*exp(W)
*/
d(W,X,Z)./*whereZ=d(W)/dX*/
...
?-d(cos(2*X+1),X,
what=2*sin(2*X
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Canyoudoeverythinginimperativeprogramming?
www.govote.at394839
start
Whydifferentparadigms?
34
Isthereaparadigmtorulethemall?
Intheoryyoucanprogram
everythinginC/C++and
imperativeprogramming,or
functionalprogramming...
Butisthat
Andisthat
FunctionalvsImperative
Doubleallthenumbersinanarray
varnumbers=
Imperative:
vardoubled=[]
for(vari=0;i<numbers.length;i++){
varnewNumber=numbers[i]*2
doubled.push(newNumber)
}
Functional:
vardoubled=numbers.map(function(n){
returnn*2
})
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36
DeclarativevsImperative
FunctionalvsImperative
Selectallthedogsthatbelongstoaspecific
Declarative:
SELECT*fromdogsINNERJOINowners
WHEREdogs.owner_id=
owners.id
Imperative:
vardogsWithOwners=[]
vardog,owner
Imperativelanguage(C/C++,Java...)
for(vardogindogs){
for(varownerinowners){
if(owner&&dog.owner_id==owner.id){
dogsWithOwners.push({dog:dog,owner:owner
})
}
}
}
Functional
Basicconstructsareimperativestatements
Changeexistingvalues,states
x=x+
y=
while(x>0)
...
Basicconstructsaredeclarative
Declarenewvalues
functionf(x){returnx+1;
Computationsareprimarilydonebyevaluatingexpressions
Pureifallconstructsaredeclarative
37
IntroductiontoFunctionalProgramming
38
Expressions
Expressions(1/2)
Expressions(2/2)
Meansofcombiningsimple
elementsintocoumpoundones
Primitiveexpressionstocapturethe
simplestelementswewantto
numbers,arithmeticexpressions...
describe
max(min(pow(3,5),-4),min(1,-2)*2)+6
2
plus
'hello'
number operator string
Callexpressions:
max (
2
,
3
)
operator operand operand
41
Names
Assignment
Bindsnamesto
a
:=
2
Nowahasthevalue2
a
plus
2
evaluatesto4
Meansofabstractingelementsby
namingandmanipulatingthem
2
a
name
max
name
plus
name
plus
name
(
2
'hello'
b
name
,
3
42
)
43
44
Whatisafunction?
Assignmentisasimplemeans
ofabstraction:bindsnamesto
values
Functiondefinitionisamore
powerfulmeansofabstraction:
bindsnamestoexpressions
Functions
46
Functiondefinition
Pureandnon-purefunction
Afunctiondefinitioncontains:
Asignaturewhichdefineshowmany
argumentsafunctiontakes
Abodywhichdefinesthecomputation
performedwhenthefunctioniscalled
function <name> ( parameterslist
return
<returnexpression>
;
Purefunctions:justreturnvalues:
Math.abs(-2)->
Math.pow(2,100)->
1267650600228229401496703205376
Non-purefunctions:haveside
effects:
)
print(-2)->
Butprint'-2'inthe
Asideeffectisnotavalue,itisanythingthat
happensasaconsequenceofcallinga
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Whatisalambda?
Closureandlambda
www.govote.at956729
start
Alambdaisafunctionwithnoname
vardoubled=numbers.map(function(n)
{
returnn*2
})
Aclosureisafunctionwithcapturedvariables
Thisseemsimple,butthisisactuallyrather
powerful!
functioncreate_function_multiplication(number)
{
returnfunction(x){returnx*number;}
}
vardoubled=
numbers.map(create_function_multiplication(2))
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50
ClosureinPython
Pythonhaslimitedsupportforlamdas:
singlestatement:
numbers.map(lambdav:v*2)
Control
Butsupportnestedfunctions
(andclosure):
defcreate_function_multiplication(number):
deffunction_multiplication(x):
returnx*number
returnfunction_multiplication
doubled=
numbers.map(create_function_multiplication(2))
51
Controlflow(1/2)
Controlflow(2/2)
Thefunctionalwayin
imperativelanguages:
Inimperativeprogramming,acontrolflow
statementexecutionresultinachoice
betweentwopaths
InJavaScript,C++,Java,Ruby...:
condition?result1:result2;
InPython:
conditionifresult1elseresult2
Exemple:if,while...
Infunctionalprogramming,itisdoneusing
aspecialfunction.
Forinstance,inLisp:
(COND
(condition1result1)
(condition2result2)
...
(TresultN))
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54
Whataboutloops?
Loopconstructsisimperative
Howwouldyouimplementthe
equivalentofaloopinfunctional?
Recursion
functionfactorial(n)
{
varr=1;
for(vari=2;i<=n;++i)
{
r*=i;
}
returnr;
}
55
Whatisrecursion?
Factorial:theclassicalexample(1/2)
Afunctioniscalledrecursiveifthe
bodyofthatfunctioncallsitself,
eitherdirectlyorindirectly.
Factorialin
factorial::Integral->Integral
factorial0=1
factorialn=n*factorial(n-1)
FactorialinCommonLISP:
(define(factorialn)
(cond((=n0)1)
(t(*n(factorial(-n1))))))
57
Factorial:theclassicalexample(1/2)
Withaloop:
Recursionvsloops
while(expression)
{
do_something();
}
functionloop_something(args...)
{
if(expression)return;
else{do_something();loop_something(args...);
}
}
(define(loop_somethingargs...)
functionfactorial(n)
{
varr=1;
for(vari=2;i<=n;++i)
{
r*=i;
}
returnr;
}
Witharecursive
functionfactorial(n)
{
return(n===0)?1:n*
factorial(n-1)
}
58
(cond(expression)value)
(t(do_something)(loop_somethingargs...))
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60
Whentouserecursionratherthaniteration?(1/4)
Whentouserecursionratherthaniteration?(2/4)
deffactorial(n):
if(n==0):
return1
else:
returnn*factorial(n-1)
Letstry:
Inmostprogramminglanguage,
thenumberoffunctioncallis
limitedbythesizeofthestack
sys.getrecursionlimit()
sys.setrecursionlimit(1003)
factorial(1000)
Tail-calloptimisation
factorial(10)
factorial(1000)
61
Whentouserecursionratherthaniteration?(3/4)
62
Whentouserecursionratherthaniteration?(4/4)
Itisamatterof
Recursionisabitmoregeneral
thanloops
Callingafunctionisusuallymoreexpensive
thanaloop
deffactorial2(n):
r=1
foriinrange(1,n+1):
r=r*i
returnr
timeit.timeit("factorial(30)","from__main__
importfactorial")
timeit.timeit("factorial2(30)","from__main__
importfactorial2")
Whenwalkingthroughatree
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Noside-effectspurefunctional
Inpurefunctional,callingafunctiononlyreturn
avalue
Theimplicationisthatcallingafunctionwiththe
sameargumentswillalwaysreturnthesame
value
Isthewithdrawfunctionpure
Advantagesandinconvenientsoffunctionalprogramming
(definebalance100)
(define(withdrawamount)
(if(>=balanceamount)
(begin(set!balance(-balanceamount))
balance)
"Insufficientfunds"))
www.govote.atentercode5445
start
66
Verificationandproving
Provingpropertiesinfunctionalprogramming
Toproveaprogramcorrect,we
mustconsidereverythinga
programdependson
Inpurefunctionalprograms,
dependenceonanydata
structureisexplicit
(define(powerbn)
(cond((=n0)1)
(t(*(powerb(-n1))))))
Claim:foranyintegern≥0andany
numberb,(powerbn)=bⁿ
Proof:
1)Verifythebasecase:(powerb
2)Assumethat(powerb(-n1))iscorrect
3)Verifythat(powerbn)iscorrectassumingthat
(powerb(-n1))iscorrect
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Concurency
Provingpropertiesinimperativeprogramming
Concurencyisoneofthecurrenthot
topicinprogramming
Themainchallengeisdata-race
Imperativeprogramsareverysensible
todata-racebecauseofstates
Thereisnodata-raceinpure
functionallanguages
functionpower(b,n){
intresult=1;
for(inti=0;i<n;+
+i)
{
result*=b;
}
returnresult;
}
Devisealoopinvariant:
(n≥i)⋀(result=bⁱ)
Provethatitistrueforthefirstloopiteration
Provethateachloopiterationpreservesit
Assumethat(n≥i)⋀(result=bⁱ)
Provethat(n≥j)⋀(result=bʲ)withj=i+
alldataisimmutable
allfunctionsarepure,withoutside-effects
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Thedownsideoffunctionalprogramming
Summaryontheupsideoffunctionalprogramming
Themainadvantageisnosideeffects
Inpractice,thereisverylimited
needforprovingaprogram
Mostlyincriticalapplications:rocketcontrol,
hospital...
Andhowdoyouprovehardware?
Verificationandproving
Concurency
Productivity?
Performanceissues(rememberfunction
callareexpensive)
Verylimitedsupport
Mostprogrammingtasksrequirestates
Ericssonclaimsanincreaseinproductivity
between9and25timeswhenusingtheir
home-grownversionofErlang
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MyKeymessageaboutprogrammingparadigms
Bepragmatic,thereisno
oneanswer!
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