Schaffert, C. et. al. 1986 An Introduction To Trellis/Owl. OOPSLA.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....most cases these works are more interested in the type theory behind object languages. ffl The language which is developed in this report contains a collection of OOPL mechanisms which are loosely based upon those of the following real life OOPLs: Smalltalk [15] C [28] Beta [20] Trellis Owl [27], Eiffel [24] and Self [29] ffl Landin [21] 22] was the first to propose functional languages as the basis for general programming language analysis. This work in this report originated in a GEC Marconi sponsored PhD undertaken by the author at Queen Mary and Westfield College, University of ....

Schaffert, C. et. al. 1986 An Introduction To Trellis/Owl. OOPSLA.

....either as a student or as a teacher depending on the context that he or she is functioning in. This situation is illustrated in figure 11(b) The object oriented methods that are studied in this paper [2 11] cannot express multiple views of objects. In languages such as C [49] Trellis Owl [66] and PAL [44] different views can be defined by the programmer with respect to the different categories of clients of an object. These mechanisms in general only distinguish between the following categories: the object itself, the subclasses of an object, and other client objects. However, they ....

C. Schaffert, T. Cooper, B. Bullis, M. Kilian & C. Wilpolt, An Introduction to Trellis/Owl, OOPSLA '86, pp. 9-16, 1986.

....a language as efficient as C but with significantly more uniformity and flexibility. 2 Language Design Research The Cecil language design began in 1991 as an attempt to combine the advantages of Self [Ungar Smith 87] CLOS [Bobrow et al. 88, Steele 90] and Trellis [Schaffert et al. 85, Schaffert et al. 86] a simple, uniform language based on dynamic dispatching, the use of multiple dispatching, and a sound static type system. The central design principle followed 2 in Cecil was to base the language on a flexible dynamic dispatching mechanism, and then to use this mechanism ubiquitously, without ....

Craig Schaffert, Topher Cooper, Bruce Bullis, Mike Kilian, and Carrie Wilpolt. An Introduction to Trellis/Owl. In OOPSLA '86 Conference Proceedings, pp. 9-16, Portland, OR, September 1986. Published as SIGPLAN Notices 21(11), November 1986.

....sub cultures. A number of object oriented database systems have been or are being developed, examples of which are GemStone [Maier et al. 1986] Orion [Banerjee et al. 1987] and Iris [Fishman et al. 1987] For programming languages there are Smalltalk [Goldberg and Robson, 1983] Trellis 1 [Schaffert et al. 1986] and CLOS [Bobrow et al. 1988] among many others. Integration efforts can build on the experiences of both the database and programming language worlds. More significantly, object orientation provides encapsulation of data and operations in such a way as to enhance the reusability, ....

Craig Schaffert, Topher Cooper, Bruce Bullis, Mike Kilian, and Carrie Wilpolt. An introduction to Trellis/Owl. In Proceedings of the Conference on Object-Oriented Programming Systems, Languages, and Applications (Portland, OR, September 1986), vol. 21, no. 11 of ACM SIGPLAN Notices, ACM, pp. 9--16.

....extensible and maintainable. One of the key reasons is dynamic binding (also known as message passing) Unfortunately, dynamic binding is slow, compared with a simple procedure call. In relatively pure objectoriented languages, such as Smalltalk [Goldberg Robson 83] Eiffel [Meyer 92] Trellis [Schaffert et al. 86] SELF [Ungar Smith 87] and Cecil [Chambers 92b] dynamic binding occurs very frequently and consequently its impact on performance is severe. For example, an efficient implementation of Smalltalk 80 runs a suite of small benchmarks 5 to 10 times more slowly than does optimized C, in large ....

Craig Schaffert, Topher Cooper, Bruce Bullis, Mike Kilian, and Carrie Wilpolt. An Introduction to Trellis/Owl. In OOPSLA '86 Conference Proceedings, pp. 9-16, Portland, OR, September, 1986. Published as SIGPLAN Notices 21(11), November, 1986.

....subclassing with subtyping Authors address, telephone, and e mail: Department of Computer and InformationSciences, E301 CSE, Gainesville, FL 32611, 904) 392 1507, graver cis.ufl.edu Department of Computer Science, 1304 W. Springfield Ave. Urbana, IL 61801, 217) 244 0093, johnson cs.uiuc.edu [Suz81, BI82, SCB 86, Str86, Mey88]. In our type system, types are based on classes (i.e. each class defines a type or a family of types) but subclassing has no relationship to subtyping. This is because Smalltalk classes inherit implementation and not specification. Our type system uses discriminated union types and signature ....

....the traditional dynamic type checking. In an untyped object oriented language like Smalltalk, classes inherit only the implementation of their superclasses. In contrast, most type systems for object oriented programming languages require classes to inherit the specification of their superclasses [BI82, Car84, CW85, SCB 86, Str86, Mey88], not just the implementation [Suz81, Joh86] A class specification can be an explicit signature [BHJL86] the implicit signature implied by the name of a class [SCB 86] or a signature combined with method preand post conditions, class invariants, etc. Mey88] Inheriting specification means that ....

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Craig Schaffert, Topher Cooper, Bruce Bullis, Mike Kilian, and Carrie Wilpolt. An introduction to Trellis/Owl. In Proceedings of OOPSLA `86, pages 9--16, November 1986. printed as SIGPLAN Notices, 21(11).

....of some existing type. We give a formal definition of legal subtyping that guarantees that verification using supertype abstraction is sound. To make such a guarantee, the notion of a legal subtype relation has to be stronger than the implementation inheritance (or subclass) relation [58] 31] [55]. The notion of legal subtyping must even be stronger than the syntactic guarantee that the new type will not cause type checking (or message not understood ) errors (see, for example, 8] It must instead be a behavioral notion, based on the specification of an abstract data type [1] 42] 40] ....

....return. Such specifications are important because they leave design decisions open for both implementors and subtypes. Our definition of legal subtype relations also provides additional intuition beyond the informal motto that each object of a subtype should act like some object of its supertypes [55], for certain kinds of incomplete specifications. For incomplete specifications which do not have a best implementation, the informal motto allows surprising behavior several objects of the subtype could collectively act differently than what one would expect from the supertype s ....

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Schaffert, C., Cooper, T., Bullis, B., Kilian, M., and Wilpolt, C. An introduction to Trellis/Owl. ACM SIGPLAN Notices, 21(11):9--16, November 1986. OOPSLA '86 Conference Proceedings, Norman Meyrowitz (editor), September 1986, Portland, Oregon.

....that most objects are not shared. Hence, the programmer is in charge to coordinate accesses to shared objects. For this purpose concurrent Trellis offers 1st class lock objects. fault tolerance. Availability: The system is implemented on a VAX 11 785 and MicroVAX running VMS. References: 166] [187] [188] 2.97 Ubik Developer: IBM Cambridge Scientific Center. Description: Describes a generalization of the Actor model. oo. memory model. parallelism. Actor language. Asynchronous message passing only. Early become for postprocessing. Return values, if any, have to be passed back by a ....

C. Schaffert, T. Cooper, B. Bullis, M. Kilian, and C. Wilpolt. An introduction to Trellis/Owl. In Proc. of OOPSLA'86, Conf. on Object-Oriented Programming Systems, Languages, and Applications, pages 9--16, Portland, Oregon, September 29 -- October 2, 1986. ACM SIGPLAN Notices 21(11).

....Gregory R. Andrews Gamma greg cs.arizona.edu Tool [63] Phi Phi Delta Delta H H A A Phi Phi Delta Delta H H A A hijklm y t i v i t c a y r a d n u o b http: www.inf.puc rio.br sergio tool Sergio E. R. de Carvalho Gamma sergio inf.puc rio.br Trellis Owl [180, 206, 207] Phi Phi Delta Delta H H A A Phi Phi Delta Delta H H A A m y t i v i t c a y r a d n u o b Ubik [83] Phi Phi Delta Delta H H A A Phi Phi Delta Delta H H A A y t i v i t c a y r a d n u o b Peter De Jong Gamma pdjong vnet.ibm.com ....

C. Schaffert, T. Cooper, B. Bullis, M. Kilian, and C. Wilpolt. An introduction to Trellis/Owl. In Proc. of OOPSLA'86, Conf. on Object-Oriented Programming Systems, Languages, and Applications, pages 9--16, Portland, Oregon, September 29 -- October 2, 1986. ACM SIGPLAN Notices 21(11).

....that the search for the operation to invoke starts with the parent of the class in which the invocation appears, instead of with the class ofself. Equivalent features using compound names (parent and operation) to specify the desired operation are provided by CommonObjects [Snyder85a] Trellis Owl [Schaffert86], extended Smalltalk We use the term extended Smalltalk to refer to the multiple inheritance extension to Smalltalk defined by Borning and Ingalls. extended Smalltalk [Borning82] and C [Stroustrup86] Because the search for the proper operation starts at a statically known class, invoking ....

Craig Schaffert, et. al. An Introduction to Trellis/Owl. Proc. ACM Conference on Object-Oriented Systems, Languages, and Applications. Portland, Oregon, Sept. 1986.

....unusual in combining a pure, classless object model, multiple dispatching (multi methods) modules, and mixed static and dynamic type checking. Cecil was inspired initially by Self [Ungar Smith 87, Hlzle et al. 91a] CLOS [Bobrow et al. 88, Gabriel et al. 91] and Trellis [Schaffert et al. 85, Schaffert et al. 86] The current version of Cecil extends the earlier version [Chambers 93a] with predicate objects, modules, and efficient typechecking algorithms. 1.1 Design Goals and Major Features Cecil s design results from several goals: Maximize the programmer s ability to develop software quickly and ....

....but all overloading is resolved at compile time based on the static types of the arguments (and results, in the case of Ada) rather than on their dynamic types as would be required for true multiple dispatching. Trellis supports an expressive, safe static type system [Schaffert et al. 85, Schaffert et al. 86] Cecil s parameterized type system includes features not present in Trellis, such as implicitly bound type variables and uniform treatment of constrained type variables. Trellis restricts the inheritance hierarchy to conform to the subtype hierarchy; it only supports isa style superclasses. ....

Craig Schaffert, Topher Cooper, Bruce Bullis, Mike Kilian, and Carrie Wilpolt. An Introduction to Trellis/Owl. In OOPSLA '86 Conference Proceedings, pp. 9-16, Portland, OR, September, 1986. Published as SIGPLAN Notices 21(11), November, 1986.

.... by the client may produce unexpected type errors in the library code that were not detected by simple testing of the library [18, page 47] Some object oriented languages need to retypecheck superclass code (potentially library code) to verify the correct use of Self types in subclasses [20]. Standard ML s transparent signatures [15] allow situations where M Usr depends on the types defined in a particular implementation of I Lib ; therefore M Usr cannot be isolated by I Lib from that implementation [13] Even when it is possible to typecheck M Usr purely against I Lib , it may ....

Schaffert, C., T. Cooper, B. Bullis, M. Kilian, and C. Wilpolt, An introduction to Trellis/Owl. Proc. ACM Conference on Object Oriented Programming Systems, Languages, and Applications, 9-16. 1986.

....It can be argued that in some application areas there are reasons to use a more restricted rule. For example, in a centralized system in which all the types are introduced by one group of programmers, one might require an explicit statement of substitutability in addition to conformance; Trellis [Schaffert 86] is a language that takes this approach. However, using a rule that is less stringent than conformity will lead to an unsafe type system, i.e. to a situation in which an undefined operation can be invoked on an object [Cook 89] The remaining sections of this paper define conformity and explain ....

....simply as t ffi a. Thus, B(t) will be type correct whenever B(p) is type correct. 5 Summary This paper has described the type system of the Emerald programming language. The basic notion underlying the type system, conformity, has been described previously with varying degrees of formality [Schaffert 86, Black 87, Cook 90, America 90] Our contributions are the extension of the basic concepts to allow both implicit and explicit polymorphism, which require the recognition that the bounding constraints of parameters cannot be expressed using conformity alone, but need the notion of matching, or ....

Craig Schaffert, Topher Cooper, Bruce Bullis, Mike Kilian, and Carrie Wilpolt. An introduction to Trellis/Owl. In Proc. First Conf. on Object-Oriented Programming Systems, Languages and Applications, pages 9--16, Portland, OR, October 1986. ACM.

....of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and or specific permission. c fl 1994 ACM xxxx xxxx xx xxxx xxxx xx.xx 2 Delta B. Liskov and J. Wing Myrhaug, and Nygaard 1970] C [Stroustrup 1986] Modula 3[Nelson 1991] and Trellis Owl[Schaffert, Cooper, Bullis, Kilian, and Wilpolt 1986], subtypes are used to broaden the assignment statement. An assignment x: T : E is legal provided the type of expression E is a subtype of the declared type T of variable x. Once the assignment has occurred, x will be used according to its apparent type T, with the expectation that if the ....

....it will also work correctly if the actual type of the object denoted by x is a subtype of T. Clearly subtypes must provide the expected methods with compatible signatures. This consideration has led to the formulation of the contra covariance rules[Black, Hutchinson, Jul, Levy, and Carter 1987; Schaffert, Cooper, Bullis, Kilian, and Wilpolt 1986; Cardelli 1988] However, these rules are not strong enough to ensure that the program containing the above assignment will work correctly for any subtype of T, since all they do is ensure that no type errors will occur. It is well known that type checking, while very useful, captures only a ....

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Schaffert, C., Cooper, T., Bullis, B., Kilian, M., and Wilpolt, C. 1986. An introduction to Trellis/Owl. In Proceedings of OOPSLA '86, pp. 9--16.

....the exception mechanism, and the mechanism for polymetric polymorphism. These ideas have had an important impact on programming language design and CLU s novel features have made their way into many modern languages. Among the languages influenced by CLU are Ada, C , ML, Modula 3, and Trellis Owl [Schaffert, 1986]. CLU is an object oriented language in the sense that it focuses attention on the properties of data objects and encourages programs to be developed by considering abstract properties of data. It differs from what are more commonly called object oriented languages in two ways. The first ....

Schaffert, Craig, T. Cooper, B. Bullis, M. Kilian and C. Wilpolt, An Introduction to Trellis/Owl, in Proceedings of ACM Conference on Object Oriented Systems, Languages and Applications, Portland, OR: September 1986.

....save and resume the control state as well as the data state of the iterator. Neither of these problems occur with CLU like iterators, since preservation of data and control state is part of their semantics. Such iterators have appeared in several other languages since CLU, e.g. Trellis Owl [Scha86]. Several database programming languages (DBPLs) which are languages designed to simplify the task of writing database applications, offer a restricted form of iterator that yields the results of a database query. Examples include Pascal R [Schm77] Plain [Wass79] and O [Agra89] These ....

Schaffert, C., Cooper, T., Bullis, B., Kilian, M., and Wilpolt, C., "An Introduction to Trellis/Owl," Proc. ACM Conf. on Object-Oriented Programming Systems, Languages and Applications, Portland, Oregon, Sept. 1986.

....of objects, to support dragging collections of items on a workstation display screen, 2 and being able to retrieve 10,000 useful , typical size objects per second from external storage into memory. 3 Typical size for languages such as CLU [29, 28] Smalltalk 80 4 [17] and Trellis 5 [38] appears to be in the range of 30 to 50 bytes, but this is 2 This number comes from informal discussion with a Smalltalk CAD tool developer at a workshop. 3 This goal came from CAD tool developers of a large computer manufacturer. 4 Smalltalk 80 is a registered trademark of PARC Place ....

SCHAFFERT, C., COOPER, T., BULLIS, B., KILIAN, M., AND WILPOLT, C. An introduction to Trellis/Owl. In Proceedings of the Conference on Object-Oriented Programming Systems, Languages, and Applications (Portland, OR, Sept. 1986), vol. 21, no. 11 of ACM SIGPLAN Notices, ACM, pp. 9--16.

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Shaffert, C., Cooper, T., Bullis, B., Killian, M. and Wilpolt, C., (1986), 'An introduction to Trellis/Owl', Proc. 1st ACM Conf. Object-Oriented Prog. Sys., Lang. and Appl, 9-16.

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Craig Schaffert, Topher Cooper, Bruce Bullis, Mike Kilian, and Carrie Wilpolt. An Introduction to Trellis/Owl. In OOPSLA '86 Conference Proceedings, pp. 9-16, Portland, OR, September, 1986. Published as SIGPLAN Notices 21(11), November, 1986.

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Craig Schaffert et al. An introduction to Trellis/Owl. SIGPLAN Notices, 21(11), November 1986. OOPSLA '86 Conference Proceedings. Ref. on page 27. BIBLIOGRAPHY 152

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C. Schaffert, T. Cooper, B. Bullis, M. Kilian, and C. Wilpolt. An introduction to Trellis/Owl. Proc. ACM Conference on Object Oriented Programming Systems, Languages, and Applications.

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C. Schaffert, T. Cooper, B. Bullis, M. Kilian, and C. Wilpot. An introduction to Trellis/Owl. In Proc. OOPSLA, 1986.

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C. Schaffert, T. Cooper, B. Bullis, M. Killian, C. Wilpot. An introduction to Trellis/Owl. In OOPSLA '86 Conference Proceedings. ACM SIGPLAN Notices 21, 11 (Nov. 1986).

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C. Schaffert, T. Cooper, B. Billis, M. F. Kilian, and C. Wilpolt. An Introduction to Trellis/Owl. In Proceedings of the ACM Conference on Object-Oriented Programming Systems, Languages and Applications, pages 9--16, Portland, Oregon, September 1986. In SIGPLAN Notices, 21(11), November 1986.

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Schaffert, C., Cooper, T., Bullis, B., Kilian, M., and Wilpolt, C. An introduction to Trellis/Owl. In Proceedings of OOPSLA '86, pages 9--16, September 1986.

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