University of Amsterdam Programming Research Group Implementation of an Imperative ... - klomp

81 Pages·2005·0.33 MB·English

University of Amsterdam
Programming Research Group
Implementation of an Imperative
Programming Language with Backtracking
Vincent Partington
Report P9712 July1997

University of Amsterdam
Department of Computer Science
Programming Research Group
Implementation of an imperative programming
language with backtracking
Vincent Partington
Report P9712 July 1997
V. Partington
CWI
P.O.Box94079
1090GB Amsterdam
The Netherlands
e-mail: [email protected]
Universiteit van Amsterdam, 1997
Implementation of an
imperative programming language
with backtracking
Doctoraalscriptievan
VincentPartington
[email protected]
Supervisor:
Prof.Dr. K.R. Apt
[email protected]
July1997
FacultyofMathematics,ComputerScience,PhysicsandAstronomy
UniversityofAmsterdam
PlantageMuidergracht24
1018VTAmsterdam

Preface
Theparadigmofimperativeprogrammingiswellknown;thefirstprogramminglanguagemostpeoplelearn
is an imperativeone, andimperativeprogramminglanguagesare oftenused for everydayprogramming.
Unfortunately, this causes many people to miss out on the advantages of logic programming, especially
wereitconcernssearchalgorithms.
Inthisreportweexplorethepossibilityofcombiningtheparadigmsofimperativeandlogicprogramming,
by implementinga compiler for an imperative languagewith the extensionsproposedin [AS97]. These
extensionsbringsomeoftheadvantagesoflogicprogrammingtoimperativeprogrammingbyintroducing
thenotionsoffailureandbacktracking,whichhaveprovensosuccessfulinlogicprogramminglanguages
likeProlog.
PartIgivesaquickoverviewofthefeaturesofthisnewprogramminglanguagecalledAlma-0,whichwas
baseduponModula-2[Wir85],anddescribestheabstractmachineusedtoimplementAlma-0(theAlma
AbstractMachine,abbreviatedtoAAA),whichcombinesthefeaturesofabstractmachinesforimperative
languageswiththoseofabstractmachinesforlogicallanguages.
PartIIdescribestheimplementationoftheAlma-0compilerindetail,fromlexicalanalysistocodegener-
ationandtherun-timesystem. Itnotonlydescribesthecurrentimplementation,butcommentarysections
describetheproblemsencounteredduringtheimplementationandthemotivationsbehindcertainsolutions.
Thesesectionshavebeendividedfromthemaintextbylargecaptions,andcanberecognizedbythelittle
“c”afterthesectionnumber.
IwouldliketothankKrzysztofAptforhissupport,andfortheenlighteningconversationsI’vehadwith
himonmanyarainymorning,and,ifoneofthemorningswasnotrainy,itshouldhavebeen,justforthe
effect. Myfellowstudentsshouldbethankedfortheirinterestingremarksanddiscussions,whetherthey
concernedmyprojectornot. Finally,IwouldespeciallyliketothankmyparentsandMichelleforkeeping
megoing,andfortellingmetogetonwithit.
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Contents
Preface iii
I Design 1
1 TheAlma-0programminglanguage 3
1.1 Extensions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Inputandoutput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3 Missingfeatures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4 Smalldifferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 TheAlmaAbstractArchitecture 9
2.1 Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3 Backtracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
II Implementation 15
3 Overviewoftheimplementation 17
3.1 Compilerstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.2 Puttingittogether . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4 Lexicalandsyntaxanalysis 21
4.1 Lexicalanalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.2 Syntaxanalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.3c Thedesignator/qualidentparseconflict . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.4c Parsinganexpressionasastatementandviceversa . . . . . . . . . . . . . . . . . . . . . 22
5 Symbolsandsymboltables 25
5.1 Differentkindsofsymbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.2 Symbolrepresentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.3 Thesymboltable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.4c Implementingtheobject-orienteddesigninC . . . . . . . . . . . . . . . . . . . . . . . . 29
6 Semanticanalysis 31
6.1 Typeanalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.2 Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
6.3 Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
6.4c WhyAlma-0hasnoCARDINALtype . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
7 Intermediatecodegeneration 39
7.1 Coderepresentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
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7.2 Translatinglanguageconstructsintocode . . . . . . . . . . . . . . . . . . . . . . . . . . 39
7.3c Orderofcodegeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
8 ImplementationoftheAAA 49
8.1 Codegeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
8.2 Run-timeenvironment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
8.3 GeneratingavalidCprogram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
8.4c Programcounteremulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
8.5c Alternativelogimplementations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Conclusionsandfurtherwork 57
A Syntaxoverview 59
A.1 Lexicalrules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
A.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
B ExampleAlma-0programs 63
B.1 knapsack.a0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
B.2 present.a0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
B.3 queens.a0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
B.4 squares.a0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Bibliography 69
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