S. Purushothaman and J. Seaman. An adequate operational semantics of sharing in lazy evaluation. In The 4th European Symposium on Programming (ESOP'92), LNCS 582, pages 435-450, Rennes, 1992.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....a consequence of using a proof technique based on denotational semantics. Many other attempts for call by need have been presented. To our knowledge, all of them are quite implementation oriented such that they suffer from low level details. We note the approaches based on explicit substitutions [PS92, ACCL91] and on graph reduction [Jef94] Structure of the Paper. As a first example we discuss the square function in a concurrent setting. We define ffi 0 in Section 3. We then introduce the notion of uniform confluence and discuss its relationship to complexity and confluence. In Section 5, we prove ....

S. Purushothaman and Jill Seaman. An adequate operational semantics of sharing in lazy evaluation. In European Symposium on Programming, volume 582 of LNCS. 1992.

....a consequence of using a proof technique based on denotational semantics. Many other attempts for call by need have been presented. To our knowledge, all of them are quite implementation oriented such that they suffer from low level details. We note the approaches based on explicit substitutions [PS92, ACCL91] and on graph reduction [Jef94] Structure of the Report. As a first example we discuss the square function in a concurrent setting. We define ffi 0 in Section 3. We then introduce the notion of uniform confluence and discuss its relationship to complexity and confluence. In Section 5, we prove ....

S. Purushothaman and Jill Seaman. An adequate operational semantics of sharing in lazy evaluation. In European Symposium on Programming (ESOP), volume 582 of Lecture Notes in Computer Science. Springer-Verlag, 1992.

....memoizing the result of computation if the susp ended object points to a thunk. This memoization saves steps when a subsequent fetch of the susp ended object is done, and hence resembles a call by need reduction strategy. Accounts of operational semantics with call by need evaluation appear in [5, 25]. The reference counting interpreter must satisfy a number of invariants in order for it to be correct: 1. The evaluation of a term in a legal store must always return a store as one of its results, i.e. the resultant store must contain no cycles of references and must have a finite domain. 2. A ....

S. Purushothaman and Jill Seaman. An adequate operational semantics of sharing in lazy evaluation. Technical Report PSU-CS-91-18, Pennsylvania State University, 1991.

....theorems of the calculus are proved in [CF58] Call by need was proposed by Wadsworth [Wad71] as an implementation technique. Formalisations of call by need on a calculus with a let construct or with environments include Ariola et al. AFM 95] Launchbury [Lau93] Purushothaman and Seaman [PS92] Yoshida [Yos93] The term icontinuationj is due to Strachey and Wadsworth [SW74] who used them to give semantics to control jumps. See Reynold [Rey93] for a history of the discovery of continuations and CPS transforms. For continuations in denotational semantics, see Gordon [Gor79] Schmidt ....

S. Purushothaman and J. Seaman. An adequate operational semantics for sharing in lazy evaluation. In Bernd Krieg-Br#ckner, editor, ESOP'92, volume 582 of Lecture Notes in Computer Science, pages 435450. Springer Verlag, 1992.

....the mismatch between the operational semantics of the lambda calculus and the actual behavior of the implementation is a major obstacle for compiler writers and users. Specifically, they cannot use the calculus to reason about sharing in the evaluation of a program. Purushothaman and Seaman [27, 29] and Launchbury [18] recently recognized this problem and developed two slightly different natural semantics of the call by need parameter passing mechanism. Roughly speaking, the semantics use store passing to describe call by need in terms of (the semantics of) assignment statements. Due to ....

Purushothaman and J. Seaman. An adequate operational semantics of sharing in lazy evaluation. In Proc. 4th European Symposium on Programming, Springer Verlag LNCS 582, 1992.

....language is to represent the memoization used in computing the fetch primitive so that certain recomputation is avioded. We aim to provide a semantics at a fairly high level of abstraction using what is sometimes known as a natural semantics [Des86, Kah87] Such a semantics has been described in [PS91] using explicit substitution and in [Lau93] through the use of an intermediate representation in which all function applications have variables as arguments. Both of these approaches are appealingly simple but slightly more abstract than we would like for our purposes in this paper. Our own ....

S. Purushothaman and J. Seaman. An adequate operational semantics of sharing in lazy evaluation. Technical Report PSU-CS-91-18, Pennsylvania State University, 1991.

....in the future, shall have a criterion for recognising the correct program transformations thus avoiding pitfalls and incorrect program transformations for compiler optimisations. There are several papers discussing a modelling of sharing in functional languages and calculus [AFM 95, Lau93, PS92, Yos93, GH90] A difference to these works is that our approach is based on a calculus of supercombinators. We model sharing using an environment like [Lau93] and reduction as in the G machine [PJ87, Aug84, Joh84] Our first main result concerns nondeterministic I O without memory, like a call ....

....nondeterminism [HO90, HO89] This approach is different from ours, since it can express amb. It is interesting that our approach only works, if sharing of expressions is treated correctly. There are several recent papers that discuss a modellig of sharing in the calculus [AFM 95, Lau93, PS92, Yos93, GH90] A difference to these works is that our approach is based on a calculus of supercombinators with fixed arities. Furthermore, due to our algorithmic definition of reduction, we have no problems in proving confluence also in the presence of cyclic reduction graphs. The use of linear ....

S. Purushothaman and J. Seaman. An adequate operational semantics of sharing in lazy evaluation. In Proc. ESOP 92, LNCS 582, pages 435--450. Springer-Verlag, 1992.

....does not at all address the laziness of implementations. The Call By Need Lambda Calculus 3 et al. 1992; Lamping, 1990) We do not deny the possible benefits of optimal reductions but instead focus on modeling the sharing used in current implementations. Our work also differs from that of Purushothaman and Seaman (1992) and Launchbury (1993) who defined an operational semantics that characterizes callby need evaluation using so called natural semantics. The basic idea behind their two formulations is the same. Roughly speaking, the semantics use store passing to describe call by need in terms of (the ....

Purushothaman, S., & Seaman, J. (1992). An adequate operational semantics of sharing in lazy evaluation. Pages 435--450 of: Proc. 4th European Symposium on Programming, Springer Verlag LNCS 582.

....proofs rather daunting. Furthermore, because the semantics was denotational, Josephs had to introduce a forcing function (corresponding to the print demand) for controlling the extent of evaluation required at any point. An operational alternative was adopted by Purushothaman and Seaman [PS92]. The authors present an operational semantics for Lazy PCF which they prove equivalent to a standard denotational semantics (observations at higher types are treated specially because of this) Their rules capture most sharing, but as many closures are built within terms, the application rule is ....

S.Purushothaman and J.Seaman, An Adequate Operational Semantics of Sharing in Lazy Evaluation, in Proc ESOP 92, Rennes, S-V, 1992.

....name c : 8 Concluding remarks We conclude with a discussion of our call by need calculus in relation to a number of other systems and notion of reduction. On other formulations of call by need. Josephs (1989) gives a continuation and storebased denotational semantics of lazy evaluation. Purushothaman and Seaman (1992) give a structured operational semantics of call by name PCF with explicit environments that is then shown to be equivalent to a standard denotational semantics for PCF. Launchbury (1993) presents a system with a simpler operational semantics and gives in addition rules for recursive let bindings ....

Purushothaman, S. and Seaman, J. (1992). An adequate operational semantics of sharing in lazy evaluation.

....can be expressed as equalities, even though the computational properties of both calculi are equivalent. Several other methods for modeling call by need have been studied. Josephs [Jos89] gives a continuation and store based denotational semantics of lazy evaluation. Purushotaman and Seaman [PS92] give a structured operational semantics of call by name PCF with explicit environments that is then shown to be equivalent to a standard denotational semantics for PCF. Launchbury [Lau93] presents a system with a simpler operational semantics and gives in addition rules for recursive ....

S. Purushothaman and Jill Seaman. An adequate operational semantics of sharing in lazy evaluation. In B. Krieg-Bruckner, editor, Lecture Notes in Computer Science 582, pages 435--450, New York, February 1992. ESOP'92, Fourth European Symposium on Programming, Springer-Verlag.

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S. Purushothaman and J. Seaman. An adequate operational semantics of sharing in lazy evaluation. In The 4th European Symposium on Programming (ESOP'92), LNCS 582, pages 435-450, Rennes, 1992.

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