Robert Cartwright and Mike Fagan. Soft typing. In SIGPLAN Conf. Programming Language Design and Impl. (PLDI), volume 26, pages 278--292, 1991.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....and having guarantees is not frozen by the language design, but is made available to the programmer. The design of this mixed type system is a subject for future research. Mixed typing is related to the concept of soft typing , an approach to type checking for dynamically typed languages [15]. In soft typing, the type checker cannot always decide at compile time whether the program is correctly typed. When it cannot decide, it inserts run time checks to ensure safe execution. Mixed typing di#ers from soft typing in that we 31 would like to avoid the ine#ciency of run time checking, ....

Robert Cartwright and Mike Fagan. Soft typing. In Proceedings of the ACM SIGPLAN '91 Conference on Programming Language Design and Implementation (PLDI), pages 278--292, Toronto, Ontario, June 1991.

....algorithms to approaches relying on principal typings. Section 6 discusses a representative sample of this related work. 1. 1 Locating Errors with Multivocal Types In the present work, we pursue an approach based on the theory of discriminative sum types, which has been developed for soft typing [7, 18, 38], and which is closely related to systems with row types [35, 29] While row types are usually indexed with record or variant labels, discriminative sum types are indexed with type constructors and the component types are the argument types of the constructors. Anticipating the formal definition ....

....purpose of typing records and variants. While row types are usually indexed with record or variant labels, discriminative sum types are indexed with type constructors and the component types are the argument types of the constructors. Similar constructions have been used for soft typing systems [7, 18, 38]. For performing the flow analysis required for error reporting, we annotate each type constructor in a discriminative type with a flow set. Row Variables r RowVar Set Variables u SetVar Sets of Type Constr s Q P (TyCon) Flow Set Ann s u : u L# # # Types t : ....

[Article contains additional citation context not shown here]

Robert Cartwright and Mike Fagan. Soft typing. In Proc. Conference on Programming Language Design and Implementation '91, pages 278--292, Toronto, Canada, June 1991. ACM.

....append(Y,Y,Z) 59 Types do not help much in this example, although Alternative (5) is given a low priority by Heuristic Rule 2 with respect to types (Section 4.4. 1) Further, if the elements of the input lists received by append were not of list type on the caller side (e.g. append( 1,2,3] [4,5,6],Out) and this information was available, Alternative (5) would have been eliminated. Additionally, Heuristic Rule 1 imposes penalty points on Alternatives (3) 4) 5) and (6) Heuristic Rule 1.1, 1.2 and 1.3 are applied to all of them, and Heuristic Rule 1.4 are applied to Alternatives (5) and ....

....to the way of handling polymorphism in our framework. Further, he proposed to pinpoint the source of errors by applying classical algorithmic debugging to a type reconstruction tree. A soft typing approach introduces static type systems to dynamically typed languages such as Lisp and Scheme [5, 1]. The MrSpidey system [10] has a programming environment that visually presents the explanation of type errors of Lisp programs based on soft typing and set based analysis [12] In this approach, debugging is performed interactively because the judgment of whether suspected fragments of a program ....

R. Cartwright and M. Fagan. Soft Typing. In Proc. ACM SIGPLAN'91 Conf. on Programming Language Design and Implementation (PLDI'91), SIGPLAN Notice 26(6), pages 268--277. ACM, 1991.

....such as Oz [Smo95, HSW95, SSW94] We aim at rejecting as many ill typed programs as feasible, but not to prove the accepted programs well typed. While strong type checking strives to maximize the number of programs for which well typedness is provable, our approach can be characterized as soft [CF91, WC94]. Our algorithm decides satisfiability of equational constraints x=y and x=f(y) and containment constraints x y modelling a weak subtype relation. The semantics of containment is axiomatized by the first order formulae: u v f(u) f(v) and x f(u) 9w(x=f(w) This formalizes the intuition ....

....to both type checking polymorphic recursion [Myc84, Hen88] and (strong) subsumption [DR90] on feature trees. We extend this correlation by showing how weak subsumption relates to soft typing. In recent years, there has been increasing interest in type analysis for untyped languages (soft typing) [Tha90, AW93, AWL94, CF91, WC94]. By far most of the typing literature is for functional languages. The close relationship between constraint solving and type inference ( Wan87, AW93, PS94] and many others) or more general program analysis (e.g. Hei92, PS94] is well established. Among the abounding literature, the work of ....

R. Cartwright and M. Fagan. Soft Typing. In ACM Conference on Programming Language Design and Implementation, pp. 278--292, June 1991.

....primarily a software engineering goal, since its key purpose is early detection of errors that would otherwise persist until run time, if they were ever noticed at all. A more common type inference application is optimization. Three specific applications are statically discharging run time casts [7, 26], eliminating virtual dispatch [3] unboxing, and alias analysis [19, 18] A high precision context sensitive abstract interpretation [24] serves such an application well. The analysis determines a set of possible run time types for each static operation in the program. If there is only one ....

....procedure call of the appropriate overriding implementation of the method. Likewise, if all run time types that reach a check satisfy the check, then the check can be removed. Polymorphism variety. Polymorphism occurs in both parametric (functional) and data varieties. Parametric polymorphism [22, 14 7, 21, 1, 2, 15, 26] refers to the ability of procedures to operate on arguments of arbitrary types, without caring what the specific type is; for example, length : list # int) Data polymorphism [9, 23] is the ability to store objects of different types in a variable or field. It is enabled by object oriented ....

[Article contains additional citation context not shown here]

R. Cartwright and M. Fagan. Soft typing. In Proceedings of the SIGPLAN '91 Conference on Programming Language Design and Implementation, pages 278--292, 1991.

....flow properties [14, 10] Because of the goals of these systems for program analysis and control flow information, the specific forms of intersection and union types are quite di#erent from the ones considered here. Systems of soft typing designed for type inference in dynamically typed languages [3] are somewhat similar and also allow intersection, union, and even conditional types [1] Again, however, the di#erent setting and goals mean that the technical realization di#ers substantially from our proposal here. 9 Conclusion We have designed a system of property types for the purpose of ....

R. Cartwright and M. Fagan. Soft typing. In Proc. SIGPLAN '91 Conf. Programming Language Design and Impl. (PLDI), volume 26, pages 278--292, 1991.

....avoiding code duplication, let ( x ( 1 2) if some complex condition ( x 3) x abc ) but doing so in general incurs explosion or even divergence of code size under the presence of recursion. How can we obtain such partial static type information in general The answer is soft typing [4, 16]: it tells us the type of each expression as far as it can be determined statically, in which case the tagging (through up casts) and type checking (through down casts) can be eliminated at translation time; otherwise, they are left to the runtime. The purpose of our work in this paper is to ....

....when necessary. For the sake of convenience, we sometimes refer to type schemes just as types in the rest of this paper when their distinction is not important. Note that we do not have polymorphic types. If we did, we could improve the precision of our analysis as in other soft type systems [4, 16], but we cannot do so (in a straightforward manner, at least) because the present type system of Java does not have parametric polymorphism. See also Section 7 for a relevant argument. 4.2 Typing Rules We define the discipline which our soft type system must follow in the form of inductive ....

R. Cartwright and M. Fagan. Soft typing. In Proceedings of the ACM SIGPLAN '91 Conference on Programming Language Design and Implementation (PLDI), volume 26, pages 278--292, 1991.

....Fewer dynamic checks required (some removed statically) All valid programs can be run. Less scheduling logic required (some removed statically) All valid programs can be scheduled. Figure 4. 1: A Comparison Between Soft Scheduling and Soft Typing Our method is to scheduling as Soft Typing [33] is to type checking (see Figure 4.1) the aim is to retain the flexibility of dynamic scheduling whilst using static analysis to remove as many dynamic checks as possible. To highlight this analogy we choose to call our method Soft Scheduling. In this chapter we describe Soft Scheduling and show ....

CARTWRIGHT, R., AND FAGAN, M. Soft typing. In Proceedings of the ACM SIGPLAN Conference on Programming Language Design and Implementation (1991), SIGPLAN, ACM.

....flow properties [14, 10] Because of the goals of these systems for program analysis and control flow information, the specific forms of intersection and union types are quite di#erent from the ones considered here. Systems of soft typing designed for type inference in dynamically typed languages [3] are somewhat similar and also allow intersection, union, and even conditional types [1] Again, however, the di#erent setting and goals mean that the technical realization di#ers substantially from our proposal here. 9 Conclusion We have designed a system of property types for the purpose of ....

R. Cartwright and M. Fagan. Soft typing. In Proc. SIGPLAN '91 Conf. Programming Language Design and Impl. (PLDI), volume 26, pages 278--292, 1991.

....be helpful in detecting errors, but unfortunately too powerful type languages can cause problems for sound type systems. They tend to force the type checker of a statically typed language to reject too many programs that should indeed be accepted. Soft typing for dynamically typed languages (e.g. [2]) employs static type checking in order to identify function calls that might be ill typed. Runtime type checks for calls that can be statically proven to be welltyped can be dropped. Soft typing does not reject any programs. The type warnings, if ignored, may result in runtime errors. ....

....type languages as found in e.g. 1] 8] or partial types as presented in [9, 10] can be processed by our type checker. Our type checker is described as an abstract interpretation and yields detailed support in detecting type errors. Furthermore, warnings of an additional sound soft typing system [2], 16] or a system with output similar to soft typing [4] can be used additionally to spot on those parts of the program that could not be proven to be well typed. A rst approach to overcome the disadvantage of soft typing not to reject any programs is given in [15] but it depends strongly on a ....

R. Cartwright and M. Fagan. Soft typing. In Proc. SIGPLAN '91 Conference on Programming Language Design and Implementation, pages 278-292, June 1991.

....in which dynamic typing and staged computation (run time code generation) coexist: all deferred computations have the same dynamic type at compile time and can be checked precisely at run time. Such a technique can handle persisting dynamic data, a weakness of our current system. Soft type systems [7] also infer types for procedures and data structures in dynamically typed programs. Advanced soft type systems [30] can be based on inclusion subtyping and can handle unions, recursive types and other complex language features. Finally, 15] presents a practical ML style type inference system for ....

R. Cartwright and M. Fagan. Soft typing. In Proceedings of the '91 Conference on Programming Language Design and Implementation, pages 278-292, 1991.

....the language s expressiveness can easily confuse the type checker. The output messages are therefore interpreted as warnings denoting those program parts which need a runtime type check and should be checked by the programmer for type correctness. This yields the concept of soft typing (see e.g. [1]) In this work we present another extension of the equality relation used by Milner [8] to type languages with nondisjoint types (that especially addresses dynamically typed languages) We introduce a commutative binary relation on types that is de ned by an algorithm CE(t1 ; t2 ) and that ....

R. Cartwright and M. Fagan. Soft typing. In Proc. SIGPLAN '91 Conference on Programming Language Design and Implementation, pages 278-292, June 1991.

....than requiring de nite values for reachability predicate, our role analysis splits according to reachability properties in the abstract role graph, which illustrates the exibility of the homomorphism based abstraction relation. Type inference algorithms for dynamically typed functional languages [2, 10] have the ability to statically approximate the values of types in higher order languages. These systems usually work with purely functional subsets of functional languages and do not consider the issues of aliasing. 7.4 Interprocedural Analyses A precise interprocedural analysis [72] extends ....

R. Cartwright and M. Fagan. Soft typing. In Proceedings of the ACM SIGPLAN '91 Conference on Programming Language Design and Implementation (PLDI), number 6 in 26, pages 278-292, 1991. 97

....there is no notion of reconstructing objects from inlined objects (wrapping) Hindley and Milner [59] Kranz et al. 54] Shao and Appel [66] and Tarditi et al. 68] have all looked into developing type inference algorithms for functional languages. The work of Cartwright et al. on soft typing [24, 71] for Scheme is also closely related to this problem. All this research has been a good starting point for Agesen [1] who has done some substantial progress in inferring concrete types for object oriented languages and their usage for compilation purposes. His methods should prove highly useful ....

Robert Cartwright and Mike Fagan. Soft typing. Proceedings of the SIGPLAN '91 Conference on Programming Language Design and Implementation, pages 278--292, 1991.

....in all of these approaches and ours appear to share some general structure, a detailed comparison among them may shed some light on the general property of a type inference based approach to program specialization. Our compilation method may also be applied to optimizing the soft type system of Cartwright and Fagan [1991] and Wright and Cartwright [1994] In the soft type system, types are implicitly treated as elements of a variant type. By checking type tag at runtime, this approach allows more exible typing than the conventional static typing. Our compilation method for polymorphic variants might be used to ....

Cartwright, R. and Fagan, M. 1991. Soft typing. In Proceedings of the ACM Conference on Programming Language Design and Implementation. ACM, New York, 278-292.

....1 u 2 may not appear in the initial set of typing assumptions. This means that, e.g. the assumption : int int intu real real real is not allowed. On the other hand, their algorithm works directly on the type constraints which makes it more feasible for an implementation. Works on soft typing [CF91, WC94, AWL94] and related systems [FP91] involve also type systems with union and intersection types but except for the above mentioned work [AWL94] these types are only used in a very restrictive way. Intersection types first appeared in connection with the intersection type discipline [CDCV80] Type ....

Robert Cartwright and Mike Fagan. Soft typing. In Proceedings of the ACM SIGPLAN'91 Conference on Programming Language Design and Implementation (PLDI'91), pages 278--292. ACM Press, 1991.

....type system has neither union types nor recursive types. Amadio and Cardelli [AC91] studied subtyping of recursive types. However, their techniques do not seem to be able to account for union and intersection types. Mishra and Reddy [MR85] Freeman and Pfenning [FP91] and Cartwright and Fagan [CF91] all defined type systems with union, intersection and recursive types. None of them did, however, consider the subtyping problem in its full generality. The work by Aiken and Wimmers [AW93] comes very close to ours. They consider a type language similar to ours, and their work is also based on a ....

Robert Cartwright and Mike Fagan. Soft typing. In Proceedings of the ACM SIGPLAN'91 Conference on Programming Language Design and Implementation (PLDI'91), pages 278--292, ACM Press, 1991.

....types . For these reasons we prefer to leave the check for closed code within the run rewrite rule. 7 Related Work Much work in dynamic typing has concentrated on soft typing : static analyses which determine when run time type checks may be safely elided from programs in untyped languages [9, 4, 15]. Solutions to the dual problem of adding dynamic types to a statically typed language appear in CLU and Cedar Mesa (see [1] for a discussion) and were first considered for ML in unpublished work of Mycroft [25] Most proposals to date have been variations on the typecase construct illustrated in ....

R. Cartwright and M. Fagan. Soft typing. In ACM SIGPLAN-91 Conference on Programming Language Design and Implementation, Toronto, Ontario, pages 278--292. ACM Press, Jun 1991.

....Multiple values may be created at any program point by using the square bracket [ notation. This statement: return [4,5] returns the pair of values h4; 5i. Multiple values must be immediately bound to variables using an init statement, or the additional values are lost; in this code: x,y] [1,2] foo( 1,2] 3,4,5] 1 Parts of the C type system library are implemented in IL2 , and Lunar s Java front end generates IL2 . IL1 is similar to IL0 but allows variable assignments. 2 In quadruple form, most instructions are of the form: r x1 x2 , where r is a name for the result, x1 and ....

....may be created at any program point by using the square bracket [ notation. This statement: return [4,5] returns the pair of values h4; 5i. Multiple values must be immediately bound to variables using an init statement, or the additional values are lost; in this code: x,y] 1,2] foo([1,2], 3,4,5] 1 Parts of the C type system library are implemented in IL2 , and Lunar s Java front end generates IL2 . IL1 is similar to IL0 but allows variable assignments. 2 In quadruple form, most instructions are of the form: r x1 x2 , where r is a name for the result, x1 and x2 are names ....

[Article contains additional citation context not shown here]

Cartwright, R., and Fagan, M. Soft typing. In Proceedings of the ACM SIGPLAN '91 Conference on Programming Language Design and Implementation (Toronto, ON, Canada, June 1991), B. Hailpern, Ed., ACM Press, pp. 278--292.

.... has extended the basic one level approach to handle the features of SELF [22] see [1] However, the problems with precision and cost inherent in a single pass approach are tackled by exploiting specialized knowledge about the SELF language [2] The soft typing system of Cartwright and Fagan [5] extends a Hindley Milner style type inference to support union and recursive types as well as insert type checks. To this Aiken, Wimmers, and Lakshman [3] add conditional and intersection types enabling the incorporation of flow sensitive information. However, these systems are for languages ....

Robert Cartwright and Mike Fagan. Soft typing. In Proceedings of the ACM SIGPLAN '91 Conference on Programming Language Design and Implementation, pages 278--292, Ontario, Canada, June 1991.

....type system has neither union types nor recursive types. Amadio and Cardelli [AC91] studied subtyping of recursive types. However, their techniques do not seem to be able to account for union and intersection types. Mishra and Reddy [MR85] Freeman and Pfenning [FP91] and Cartwright and Fagan [CF91] all defined type systems with union, intersection and recursive types. None of them did, however, consider the subtyping problem in its full generality. The work by Aiken and Wimmers [AW93] comes very close to ours. They consider a type language similar to ours, and their work is also based on a ....

Robert Cartwright and Mike Fagan. Soft typing. In Proceedings of the ACM SIGPLAN'91 Conference on Programming Language Design and Implementation (PLDI'91), pages 278--292, ACM Press, 1991.

....global analyses and transformations, we are able to suppress more unnecessary checks and transitions. Also, by working on program abstractions, our framework is more general than the restriction to finite state automata may lead one to think (as hinted at in Section 5. 2) Soft typing (see e.g. [2]) is a mixed approach for enforcing type safety. A soft type checker does not reject statically ill typed programs but inserts dynamic type checks where necessary. Its goal is similar to ours: retaining flexibility for the minimum runtime cost. There are many other works about the enforcement of ....

R. Cartwright and M. Fagan. Soft typing. In Proceedings of PLDI '91, Conference on Programming Language Design and Implementation (Toronto, Canada), pages 278--292, June 1991.

....global analyses and transformations, we are able to suppress more unnecessary checks and transitions. Also, by working on program abstractions, our framework is more general than the restriction to finite state automata may lead one to think (as hinted at in Section 5. 2) Soft typing (see e.g. [2]) is a mixed approach for enforcing type safety. A soft type checker does not reject statically ill typed programs but inserts dynamic type checks where necessary. Its goal is similar to ours: retaining flexibility for the minimum runtime cost. There are many other works about the enforcement of ....

R. Cartwright and M. Fagan. Soft typing. In Proceedings of PLDI '91, Conference on Programming Language Design and Implementation (Toronto, Canada), pages 278--292, June 1991.

....Dynamically typed languages usually tag values with types so that type checking may be performed at run time. Since the shape of an object can usually be determined from the tag, implementing polymorphic features in such a language is not difficult. However, recent work on soft typing [5, 11, 1] has shown that many of the run time type tests can be eliminated at compile time by using type inference. In order to eliminate most tests, the inference systems are based on parametrically polymorphic type systems. Consequently, techniques used to implement parametric polymorphism for statically ....

R. Cartwright and M. Fagan. Soft typing. In Proceedings of the ACM SIGPLAN '91 Conference on Programming Language Design and Implementation, pages 278--292, June 1991.

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Robert Cartwright and Mike Fagan. Soft typing. In SIGPLAN Conf. Programming Language Design and Impl. (PLDI), volume 26, pages 278--292, 1991.

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R. Cartwright and M. Fagan. Soft typing. In Proc. SIGPLAN '91 Conf. Programming Language Design and Impl. (PLDI), volume 26, pages 278--292, 1991.

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Robert Cartwright and Michael Fagan. Soft typing. In Proc. SIGPLAN '91 Conference on Programming Language Design and Implementation, pages 278--292. ACM, June 1991.

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Robert Cartwright and Mike Fagan. Soft typing. In SIGPLAN Conf. Programming Language Design and Impl. (PLDI), volume 26, pages 278--292, 1991.

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R. Cartwright and M. Fagan. Soft typing. In Proc. SIGPLAN '91 Conf. Programming Language Design and Implementation (PLDI), volume 26, pages 278--292, 1991.

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R. Cartwright and M. Fagan. Soft typing. In SIGPLAN Conf. Programming Language Design and Impl. (PLDI), volume 26, pages 278--292, 1991.

No context found.

Robert Cartwright and Mike Fagan. Soft typing. In Proceedings of the '91 Conference on Programming Language Design and Implementation, pages 278-292, 1991.

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R. Cartwright and M. Fagan. Soft typing. In PLDI, pages 278--292, June 1991.

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R. Cartwright and M. Fagan. Soft typing. In SIGPLAN Conf. Programming Language Design and Impl. (PLDI), volume 26, pages 278--292, 1991.

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R. Cartwright and M. Fagan. Soft typing. In Proceedings of the ACM SIGPLAN '91 Conference on Programming Language Design and Implementation (PLDI), pages 278--292, 1991.

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R. Cartwright, M. Fagan, "Soft Typing", Proceedings of the SIGPLAN '91 Conference on Programming Language Design and Implementation.

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Robert Cartwright and Mike Fagan. Soft typing. In PLDI, pages 278--292, 1991.

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R. Cartwright and M. Fagan. Soft typing. In Proc. SIGPLAN '91 Conf. Programming Language Design and Impl. (PLDI), volume 26, pages 278--292, 1991.

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R. Cartwright and M. Fagan. Soft typing. In Proc. SIGPLAN '91 Conf. Programming Language Design and Impl. (PLDI), volume 26, pages 278-292, 1991.

No context found.

Robert Cartwright and M. Fagan. Soft typing. In Proceedings of the '91 Conference on Programming Language Design and Implementation, pages 278--292, 1991.

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R. Cartwright and M. Fagan. Soft typing. In Proceedings of the '91 Conference on Programming Language Design and Implementation, pages 278--292, 1991.

No context found.

R. Cartwright and M. Fagan. Soft typing. In SIGPLAN Conf. Programming Language Design and Impl. (PLDI), volume 26, pages 278--292, 1991.

No context found.

R. Cartwright and M. Fagan. Soft typing. In Proceedings of the '91 Conference on Programming Language Design and Implementation, pages 278--292, 1991.

No context found.

R. Cartwright and M. Fagan. Soft typing. In Proc. SIGPLAN '91 Conf. Programming Language Design and Impl. (PLDI), volume 26, pages 278-292, 1991.

No context found.

R. Cartwright and M. Fagan. Soft typing. In Proceedings of the '91 Conference on Programming Language Design and Implementation, pages 278--292, 1991.

No context found.

R. Cartwright and M. Fagan. Soft typing. In Proc. SIGPLAN '91 Conf. Programming Language Design and Impl. (PLDI), volume 26, pages 278--292, 1991.

No context found.

Robert Cartwright and Mike Fagan. Soft typing. In Proc. SIGPLAN '91 Conference on Programming Language Design and Implementation, pages 278--292, June 1991.

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Cartwright, R. and Fagan, M. Soft Typing. Proceedings of the ACM SIGPLAN 1991 Conference on Programming Language Design and Implementation

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R. Cartwright and M. Fagan. Soft typing. In Proceedings of the ACM SIGPLAN '91 Conference on Program- ming Language Design and Implementation (PLDI), number 6 in 26, pages 278-292, 1991.

No context found.

R. Cartwright and M. Fagan. Soft typing. In Proceedings of the ACM SIGPLAN '91 Conference on Programming Language Design and Implementation (PLDI), number 6 in 26, pages 278-292, 1991.

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R. Cartwright and M. Fagan. Soft typing. In Proceedings of the ACM SIGPLAN '91 Conference on Programming Language Design and Implementation (PLDI), number 6 in 26, pages 278-292, 1991.

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