45 YEARS OF RESEARCH AND TEACHING IN COMPUTER SCIENCE

Transcription

1 45 YEARS OF RESEARCH AND TEACHING IN COMPUTER SCIENCE Neil D. Jones Professor emeritus, DIKU, University of Copenhagen

2 HOW THE TALK IS ORGANISED Historical 1959-present Research activities and directions, ph.d. and m.sc. work Insights, questions People who ve been important in this: students, colleagues, guests 1

3 TWO THREADS Programming languages and compiler construction Computability theory 2

4 STUDENT PROGRAMMER : Southern Illinois University undergraduate studies in math; student programmer Great discovery: I could do what I enjoyed, and get paid for it(!) Odds and ends: statistics package; Newton s method for bid on missile shield remover; math function subroutines for ALGOL 58 compiler first compiler project (0-pass load-and-go SOAP assembler) 3

5 start work on PROGRAMMING LANGUAGES by COMPILER CONSTRUCTION : Computer Science department at University of Western Ontario Full-time teaching and programming; Ms, Phd studies on my own time Designed, programmed ALGOL 60 compiler (4 years from 1962; showed need for precise semantics) Cobol student system (interpreter) taught (compilers, computability, general system theory,...) In those days, a compiler could not be a thesis 4

6 INSIGHTS, QUESTIONS Bootstrapping works! A compiler is a semantics-preserving function from programs to programs But what is a program s semantics? Hmm... 5

7 start work on COMPUTATION THEORY Inspired by Smullyan s 1961 Princeton thesis: Theory of Formal Systems (diagonalisation! strings!) 1965 MS thesis: A survey of formal language theory. Supervisor Satoru TAKASU a paper accepted with a bug (oops!) (main theorem s negation was proven 25 years later by another guy named Neil) 1967 PhD thesis: Formal languages and rudimentary attributes. Supervisors TAKASU and Arto SALOMAA 6

8 INSIGHTS, QUESTIONS Diagonalisation is fun! (though mind-bending) Grammars/recursive functions/... work at a pleasing level of abstraction Proofs should be clear and convincing Open question: NSP ACE(n) =? DSP ACE(n) 7

9 COMPUTABILITY, COMPLEXITY, PARSING : Pennsylvania State University. complexity theory: book: Computability Theory (partly based on phd thesis) first paper formulating completeness for NLOGSPACE solve the spectrum problem (with Alan Selman) students: Hal Sudborough, 3 other phds learn theory and practice of LR parsing 8

10 INSIGHTS, QUESTIONS Much on understanding properties of some sets: Call space, all run-time states of a given program All evaluation contexts of a first-order logic formula All parser states that occur while parsing an input string 9

11 COMPLEXITY AND PROGRAM FLOW ANALYSIS : University of Kansas. collaboration with Steve Muchnick, quite a few good papers complexity: first paper formulating completeness for PTIME (with M.Sc. student Bill Laaser) new complete problems for NLOGSPACE complexity of Petri net analysis begin program flow analysis (as yet, no formal semantics) 10

12 INSIGHTS, QUESTIONS The excitement of discovering good definitions Reduction of one problem to another Even simple programs are hard to analyse 11

13 PLAYING ON BOTH STRINGS : Aarhus University. Visiting professor complexity of Lindemayer systems complexity of program analysis 12

14 HIGH GEAR IN PROGRAM FLOW ANALYSIS : University of Kansas learn of Patrick and Radhia Cousot s work on abstract interpretation shape analysis by grammars and by k-limited graphs write book: Binding Times and Parameter Passing (with Steve Muchnick) edit book: Program Flow Analysis (with Steve Muchnick) 13

15 FINALLY, SEMANTIC FOUNDATIONS FOR FLOW ANALYSIS Aarhus University again attribute grammars (complexity, aid in parsing) learn denotational semantics (the best possible teachers: 1980 workshop at Aarhus: Peter Mosses, Gordon Plotkin, Robin Milner) Semantics-directed Compiler Generation (more a grand dream than a reality) students (!): Dave Schmidt (phd), Flemming Nielson, Henning Christiansen 14

16 INSIGHTS, QUESTIONS More and more general levels of abstraction but... Scott domains and denotational semantics don t mix esily with operational semantics and compiler optimisations It can be hard to keep up with talented students 15

17 BEGINNING OF THE TOPPS GROUP : Copenhagen University. first DIKU M.Sc students (!): Mads Tofte and Klaus Havelund CERES compiler generator (started with Henning Christiansen, then Mads Tofte, who wrote a book) Develop and teach Datalogi 2 (programming languages and compilers) collaboration with others, e.g., Alan Mycroft, Flemming Nielson 16

18 EXCITING TIMES AT COPENHAGEN UNIVERSITY 1983: learn about partial evaluation, potential of Futamura projections for compiler generation 1983: meet Andrei Ershov at a conference no, the Futamura projections don t exist in practice (aha!!) : a year s work with Peter Sestoft, Harald Søndergaard ending in a solution: a program mix 1985: first paper on self-applicable partial evaluation 17

19 INSIGHTS, QUESTIONS A good problem statement is worth gold (N.B. the Futamura projections) A hack elevated to a principle: binding-time annotations Self-application can be used constructively, not only for negative results like unsolvability of the halting problem, complexity lower bounds A way to say: able to remove all interpretational overhead 18

20 EXCITING TIMES AT COPENHAGEN UNIVERSITY, CTD. meet Olivier Danvy at Rewriting Techniques and Applications 1985 DIKU conference: Programs as Data Objects 1987: Dines Bjørner organises Gammel Avernæs meeting on partial evaluation (14 countries, 65 people, 16 here today) 19

21 1987-PRESENT: MANY GOOD PH.D. STUDENTS (all with published papers, most here today) Lars Ole Andersen Anders Bondorf Niels Christensen Hans Dybkjær Carsten Gomard Henning Makholm Torben Mogensen Kristoffer Holm Rose Jens Peter Secher Peter Sestoft Sebastian Skalberg Harald Søndergaard Morten Heine Sørensen Morten Welinder 20

22 plus... TOPPS-PUBLISHED PAPERS in Complexity or computability (excuse omissions!) by Colleagues: Students: Guests: Nils Andersen Torben Amtoft Amir Ben-Amram Klaus Grue Carl Frederiksen Lars Kristiansen Jakob Simonsen Eva Rose Jesper Träff 21

23 plus... TOPPS-PUBLISHED PAPERS in Partial evaluation or program analysis (excuse omissions!) by Colleagues: Students: Students: Guests: Nils Andersen Torben Amtoft Thomas Jensen Amir Ben-Amram Andrzej Filinski Jesper Andersen Jesper Jørgensen Olivier Danvy Robert Glück James Avery Karoline Malmkjær John Hannan Fritz Henglein Lars Birkedal Christian Mossin Rene Hansen Julia Lawall Nina Bohr Kristian Nielsen John Hatcliff Torben Mogensen Søren Debois Henning Niss Chin Soon Lee Mads Tofte Carl Frederiksen Jakob Rehof Jean-Yves Moyen Johan Gade Mads Rosendahl Dave Sands Arne Glenstrup Bjarne Steensgaard 22

24 1993 BOOK Partial Evaluation and Automatic Program Generation co-authored with Peter Sestoft and Carsten Gomard 23

25 MORE TOPPS ACTIVITIES PEPM (Partial Evaluation and Program Manipulation) started in 1991, held yearly since then, plus one ASIA-PEPM research projects: NSF (USA), several Danish; EU/ESPRIT: Semantique, Atlantique, Abile, Daedalus guest professorships many visiting DIKU, including Ben-Amram, Danvy, Hannan, Hatcliff, Horwitz, Kristiansen, Leuschel, Liu, Mauborgne, Melton, Milliken, Moyen, Reps, Paige, Sagiv, Sands, Turchin, Urzyczyn, Voda, Yokoyama Neil: several, a month or so at 4 Paris, Sophia-Antipolis, Kyoto, 2 Singapore, Oxford 24

26 A SHIFT OF RESEARCH DIRECTION Back towards computability and complexity theory: linear-time hierarchy ( constant factors do matter ) read-only programs life without cons expressive power of higher-order types 25

27 INSIGHTS, QUESTIONS It s interesting to ask operational questions about theoretical constructions Some of these can be answered when given limited computation time or space (else all is undecidable!) Many open questions about programs, e.g., is recursion more powerful than iteration? are equivalent to well-known open problems in complexity, e.g., is PSPACE = LOGSPACE? 26

28 1997 BOOK chapters by Amir Ben-Amram Torben Mogensen Morten Heine Sørensen Computability and Complexity from a Programming Perspective 27

29 60TH BIRTHDAY WORKSHOP/FEST Held in Aarhus in 2001 Festchrift published (LNCS 2566 beautiful!) Authors: 44, including many mentioned before The hard-working editors: Torben Mogensen David Schmidt Hal Sudborough 28

30 LOCAL ORGANISER FOR A BIG MEETING FLoC 2002: Federated Logic Conferences 7 main meetings (CADE, CAV, FME, ICLP, LICS, RTA, TABLEAUX) 33 workshops Major help from lots of friends. (Thanks again!) 29

31 2001-PRESENT: A SWING BACK TO PROGRAMS Aim: better to understand properties of call space the set of all run-time states of a given program. tupling analysis size-change termination Plus ça change, plus c est la même chose (with Siau Cheng Khoo, Wei-Ngan Chin) (with Amir Ben-Amram, Nina Bohr, Chin Soon Lee, Damien Sereni) analysis of program running times (with Carl Frederiksen, Lars Kristiansen) using temporal logic in program analysis, transformation (w/carl Frederiksen, Rene Hansen, D.Lacey, Eric Van Wyk) 30

32 MANY THANKS to the organisers Fritz Henglein, Julia Lawall, Dave Schmidt DIKU: Ruth Schlüter and (last but not least) the participants: close friends, colleagues, ex-students, people inspired by programs as data objects. So long, and thanks for all the f i s h research! 31