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From VDL to VDM Cliff Jones University of Newcastle

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1 From VDL to VDM Cliff Jones University of Newcastle cliff.jones@ncl.ac.uk

2 2001-05-18Lucas Colloquium2 Why I want to talk about this  In honour of Peter!  “move operational to denotational”  trivialises  Tagebucher!  now teaching semantics (again)  chose operational  have a clearer view of what was achieved

3 2001-05-18Lucas Colloquium3 1968 and PL/I  Version 3 of ULD-III  ULD-I = (natural language) manual  ULD-II Hursley  chain search for locations  name “VDL”  Jo  ULD-III course (April?)  assignment started August(?)  wonderful 2 years

4 2001-05-18Lucas Colloquium4 Pre 1968 (i)  “NPL”  Baden-bei-Wien meeting 1964  McCarthy, Elgot, Landin  recursive int function  nothing on non-determinism  nothing on errors  “abstract objects”  “Tentative Steps” TR25.???  See [LuWa69] on VDL – ULD-III(vers 1) 1965

5 2001-05-18Lucas Colloquium5 Pre 1968 (ii)  what had to be invented  sets, maps, sequences, :: (  )  handling goto and exceptions  how to handle non-determinism  parallelism (as merging) for tasking  storage models  challenge for Peter’s retirement: maths of this  a notation for handling all of the above  a system for checking/printing

6 2001-05-18Lucas Colloquium6 Other gems!  axioms of stack!!  [LuWa69]  block structure proof  [Lu68] TR25.085  compiler proof  [Lu??] Italy

7 2001-05-18Lucas Colloquium7 68/70 compiler design  lots of experiments (Hen style!)  new versions of block structure proofs  “retrieve function” idea  exit/tixe in OS framework  see [JoLu71] LNM188  most difficult (tedious) lemma  Scott’s visit [Scott deB69]  sketch: development method for compilers

8 2001-05-18Lucas Colloquium8 Jo 1970/72  own “Ad Tech” group in Hursley  “functional semantics”  exec: Stmt x Env x Store  Store  exit  “Earley story”  challenge from colleagues  axiomatic approach to reification  basis of VDM for “normal” programs  pre/post (of 2 states)  data reification (with retr)

9 2001-05-18Lucas Colloquium9 What did GDP’s SOS bring?  a notation for OS  fits “judgements” in logic  a stronger prompt to separate  env (  ) vs store (  )  tricks with decorated arrows don’t scale  a brilliant way to show non-determinism  see [Plo81]

10 2001-05-18Lucas Colloquium10 New statement in an OOL a  dom O mk-Oinfo(c, act, sl, st, cl) = O(a) hd sl = mk-New(v, c’) b  Oid -  dom O) -------------------------------------------------------------------- exec(C, O) = O † {a  mk-Oinfo(c, act, tl sl, st † {v  b , cl), b  mk-Oinfo(c’, quies, [], {v  nil | v  dom s-tpm(C(c’)) }

11 2001-05-18Lucas Colloquium11 1972 call from Lu  PL/I compiler for FS  choose method  “yes”  who else can we get?  working papers pre ’73 start  switch to “Denotational”  Bekic/Landin  “functional semantics”  luck that ECMA/ANSI dropped tasking

12 2001-05-18Lucas Colloquium12 “VDM”  denotational  plus combinators  plus exit/tixe  cf. “continuations”  could read as OS  origin of name  Bj! … and those wicked fruit cocktails! ... but, better than “Meta-IV”

13 2001-05-18Lucas Colloquium13 Some memories   on the whiteboard (3 rd floor)  then worked fairly independently  Walk: “no Greek letters”  all in our grasp  tools needed for changes  assumed FS more stable than PL/I  Pok definition of FS  Tony Peacock, M-JH  executable, optimised  Be version

14 2001-05-18Lucas Colloquium14 Conclusion  most stimulating collaboration of my career!  “St Valentine’s day massacre” (of FS)  attempts to define new role for Wien  Diaspora  publication, dissemination  influence:  VVSL, RAISE, B,...

15 2001-05-18Lucas Colloquium15 A (history) commercial  “Semantics and Verification”  Science Museum, London  June 5 th  Stoy  Milner  Hoare  Landin!

16 2001-05-18Lucas Colloquium16 References  VDM of PL/I  TR25.139  Books: LNCS#61, 177  Lu “twin”  TR25.085  History notes  “Storia” paper  FM’99

17 From VDL to VDM Cliff Jones University of Newcastle cliff.jones@ncl.ac.uk


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