Kazunori Ueda and Masao Morita. Moded flat GHC and its message-oriented implementation technique. New Generation Computing, 13(1):3--43, 1994.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....the cost of searching intended programs. For example, few instances and program schema in which variable occurrences are missing might be su#cient for programming. 1. 1 Concurrent Logic Programming The mechanism of error correction in Kima is based on the mode and type systems of Moded Flat GHC [35, 36]. Moded Flat GHC is a concurrent logic (and consequently, a concurrent constraint) language with a constraintbased mode system. Concurrent logic languages [32] provide a simple and powerful model of concurrency as well as a full fledged programming language with . first class message channels, ....

....GHC allows us to solve a set of mode constraints obtained from program text as a constraint satisfaction problem. Mode reconstruction statically determines the read write capabilities of variable occurrences and establishes the consistency of communication protocols between concurrent processes [36]. In other words, mode reconstruction guarantees the cooperative use of shared variables between concurrent processes. By cooperative we mean exactly one process can determine each part of a data structure (such as a stream of messages) communicated between processes. The constraint satisfaction ....

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K. Ueda and M. Morita. Moded Flat GHC and Its Message-Oriented Implementation Technique. New Generation Computing, 13(1):3--43, 1994.

....Thus we have provided a denotational semantics for such programs programming languages, which goes beyond the usual success based SLD resolution mechanism of logic programming. Input consuming derivations bear a certain resemblance with derivations in the language of Moded (Flat) GHC [32]. Actually, input consuming programs can be seen as a simplified version of moded GHC, and the results we provide here can be thus applied to some moded GHC programs. We want to note however that Moded (F)GHC is a full fledged programming paradigm, while input consuming programs are meant for ....

K. Ueda and M. Morita. Moded flat GHC and its message-oriented implementation technique. New Generation Computing, 13(1):3--43, 1994.

....programming by restricting its descriptive power somewhat and doing aggressive optimization based on static program analysis. The crucial point here is not to do so in an ad hoc manner. We have thus far developed a constraint based mode system for Flat GHC that enables static dataflow analysis [6, 10]. The resulting language is called Moded Flat GHC. This approach is similar in essence to static type systems found in many languages, and is considered one of the most systematic approaches to syntactic restriction and static analysis. The following observations have been obtained from several ....

....platform for the study of efficient array operations in nonprocedural languages. Furthermore, the facts ffl that the language does not have the notion of destructive assignments and distinguishes between old and new arrays and 1 To be exact, the mode system assumes extended occur check [10] that excludes the unification between identical variables, but ordinary programs do not perform such unification. 2 ffl that all data created and referenced by concurrent processes should explicitly appear as goal arguments are considered even beneficial for program analysis and optimization ....

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Ueda, K. and Morita, M., Moded Flat GHC and Its Message-Oriented Implementation Technique. To appear in New Generation Computing, 1994. 9

....contains essentially four contributions to solving the above problems. In order to provide a characterization of dynamic scheduling that is reasonably abstract and hence amenable to semantic analysis, we consider inputconsuming derivations [16] a formalism very similar to the one of Moded GHC [18]. Roughly speaking, in an input consuming program only atoms whose input arguments are not instantiated through the uni cation step are allowed to be selected. Moreover, we restrict our attention to the class of simply moded programs, which are programs that are, in a well de ned sense, consistent ....

....provided only a sucient condition) As mentioned in Section 4.2, in the context of parallelism and concurrency [15] one can have derivations that never succeed, and yet compute substitutions. Moreover, input consuming derivations essentially correspond to the execution mechanism of (Moded) FGHC [18]. Thus we have provided a model theoretic semantics for such programs programming languages, which go beyond the usual success based SLD resolution mechanism of logic programming. On a more practical level, our semantics for partial derivations is used in order to prove termination. In the ....

K. Ueda and M. Morita. Moded Flat GHC and its message-oriented implementation technique. New Generation Computing, 13(1):3-43, 1994.

....This paper contains essentially four contributions tackling the above problems. In order to provide a characterisation of dynamic scheduling that is reasonably abstract and hence amenable to semantic analysis, we consider inputconsuming derivations [18] a formalism similar to Moded GHC [20]. In an inputconsuming derivation, only atoms whose input arguments are not instantiated through the unification step may be selected. Moreover, we restrict our attention to the class of simply moded programs, which are programs that are, in a well defined sense, consistent wrt. the modes. As also ....

....yes rewrite(In,Out) yes no descendant(Out,In) yes yes yes transform(In,In,In,Out) yes yes yes holds(In,Out) yes yes yes twoleast(In,Out) no Table 3. Programs from Lindenstrauss s Collection Moreover, input consuming derivations essentially correspond to the execution mechanism of (Moded) FGHC [20]. Thus we have provided a model theoretic semantics for such programs programming languages, which go beyond the usual success based SLD resolution mechanism of logic programming. On a more practical level, our semantics for partial derivations is used in order to prove termination. We have ....

K. Ueda and M. Morita. Moded Flat GHC and its message-oriented implementation technique. New Generation Computing, 13(1):3--43, 1994.

....Widening introduces approximation into the fixpoint calculation, allowing a upper approximation of the least fixpoint to be computed finitely, even in a domain containing infinite increasing chains. 3.2. Modes The correctness of the demand collecting semantics relies on programs being well moded [33]. We assume a coarse form of modes that divides arguments into input and output. We assume that program atoms have the form p(x; y) where x is a 1 Allowing program variables within unions and fixpoints adds technical problems to the construction with no significant benefit in expressivity. 10 ....

....x is a 1 Allowing program variables within unions and fixpoints adds technical problems to the construction with no significant benefit in expressivity. 10 vector of input variables and y is a vector of output variables. It would be necessary to generalize this to richer modes (e.g. those in [33]) if we were going to handle two way streams. However, we use the coarser form here, as it is adequate for one way streams. It is occasionally necessary to refer to the output variables of an agent in the program. We let Out(p(x; y) y. For compound agents, we presume a consistent moding ....

K. Ueda and M. Morita. Moded Flat GHC and its Message-Oriented Implementaton Technique. New Generation Computing, 13(1):3--43, 1994. 32

....of c occur in input positions of A, 2. if B is a selectable atom and H is the head of a clause of P that can be applied to B, then B restricted to its input positions is an instance of H restricted to its input positions. Observe that the program sieve is mode driven. In the language moded GHC [21], using guarded Horn clauses, an atom is selectable if requirements similar to the ones of mode drivenness hold. These restrictions imply some properties that are used to prove the main result. If in a request configuration the request is not satisfied, then there is a demanded atom. Moreover, if ....

K. Ueda and M. Morita. Moded flat GHC and its message-oriented implementation technique. New Generation Computing, 13(1):3--43, 1994.

.... we have taken can also be seen as an application of the theoretical framework developed by Bueno et al. 21, 3] A different problem, which shares some similarities to what we are considering in this context, is represented by the management of parallel tasks in committed choice languages [33]. 4.1 Overview The process of DAP annotating a program can be intuitively seen as the process of designing a function, R, which given a clause, returns a list of parallelizable shared variables and a partitioning of the body goals into sets of subgoals that can be executed in DAP. Formally, R : ....

K. Ueda and M. Morita. Moded Flat GHC and its Messageoriented Implementation Technique. New Generation Computing, 1993.

....are ambiguities on which inputs connect to which outputs, etc. We have implemented a VDP system based on a visual parallel programming environment KLIEG, which answers the above issues. KLIEG itself is a visual parallel data flow language based on a parallel logic programming language, moded FGHC [10]. We refer to a VDP in KLIEG as a KLIEG VDP. Designers can define KLIEG VDPs that retain design information as patterns, and then users choose a pattern from a catalog of KLIEG VDPs in their programs and implement customized processes in the pattern. The features of the KLIEG VDP are as follows: ....

....connects the ports correctly if the types of all ports are detected. In this way, the user does not have to reconnect each port every time when replacing the processes. To implement these type checkings, we use a constraint based type analysis. The base language of KLIEG is moded FGHC [10], and our analysis technique is also based on the mode analysis algorithm of moded FGHC. We omit the details of the algorithm for brevity; interested readers are referred to [10] 3 Programming with KLIEG VDPs For users, programming using KLIEG VDPs is simple and easy. It can be performed using ....

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Kazunori Ueda and Morita Masao. Moded Flat GHC and Its Message-Oriented Implementation Technique. New Generation Computing, Vol. 13, No. 1, pp. 3--43, 1994.

....Widening introduces approximation into the fixpoint calculation, allowing a safe upper approximation of the least fixpoint to be found finitely, even in a domain that contains infinite increasing chains. 3. 3 Modes The correctness of the collecting semantics relies on programs being well moded [12]. In the present development, we assume a coarse form of modes that divides arguments into input and output. We assume that program atoms have the form B( x; y) where x is a vector in input variables and y is a vector of output variables. It would be necessary to generalize this to richer ....

....and output. We assume that program atoms have the form B( x; y) where x is a vector in input variables and y is a vector of output variables. It would be necessary to generalize this to richer modes if we were going to handle two way streams. The more expressive notion of moding found in [12] would be perfectly suited to our technique. However, we use the coarser form here, as it is adequate for presentation of our technique. Below it is occasionally necessary to refer to the output variables of an agent in the program. We let Out(B( x; y) y. For compound agents, we presume a ....

Masao Morita Kazunoria Ueda. Moded flat ghc and its message-oriented implementaton technique. New Generation Computing, 1994.

....significant work by some sort of scheduler process thus it is entirely possible for the scheduler to become the limiting factor in execution performance. This thesis suggests a two step approach to alleviating these problems, along lines explored earlier by others including Ueda and Morita [30, 31], Tick and Korsloot [19] and King and Soper [15, 17, 16] First, the program is statically analyzed to discover where variables will be bound. This analysis allows traditional compiler optimizations to be applied to the compilation of FGHC programs, and also provides a framework for a second ....

....the programmer may explicitly supply query modes to the analyzer by preloading the partition table. It is important to note that moded FGHC is a strict subset of FGHC , in the sense that there exist correct and meaningful FGHC programs which are nonetheless not moded. However Ueda s assertion in [31] that Fortunately, most GHC programs written so far are written, or can be easily rewritten, following these conventions seems to be correct. Perhaps the most common moding error in common use is the use of passive unification in body goals to select elements. Thus, the program of Figure 2.6 is ....

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K. Ueda and M. Morita. Moded Flat GHC And Its Message-Oriented Implementation Technique. New Generation Computing, 1992. To Appear.

....and error goals to be diagnosed, we need to modify KLIC s error handler so that the offending goal s arguments are displayed for debugging purposes. KLIC s postmortem facility should allow this to be done. Our current prototype only works for programs that are well moded, in the sense of (Ueda and Morita, 1994). However, our system should also handle programs that are not well moded: even if the language requires programs to be well moded, the program to be analysed may not be because it presumably contains bugs. More complex run time support is required to handle non well moded programs: the producer ....

K. Ueda and M. Morita. 1994. Moded Flat GHC and its message-oriented implementation technique. New Generation Computing 13, 1, pp. 3--43.

....5. Instead of output unification, variables were allowed only one producer and, in some languages, only one consumer. 1.3. Reform Prolog 5 Examples of languages which exhibit one or more of these simplifications are: Concurrent Prolog [173, 174] FCP [175, 226] Parlog [53, 54] F)GHC [203, 204], Strand [77] and Janus [168] These simplifications made it harder to write programs in these languages, the introduction of explicit concurrency being one of the main reasons. The following quote is from Tick s book on parallel logic programming [193, p. 410] The book contains many programs ....

K. Ueda, M. Morita, Moded Flat GHC and Its Message-Oriented Implementation Technique, New Generation Computing, 13(1):3--43, 1994. --5

....programs, including committed choice programs, no syntactic distinction is made between variables and their subterms which have output mode and are thus being bound in an occurrence, and those which have input mode and are thus being read in an occurrence. Thus, some form of mode analysis (e.g. [29, 32]) or mode declarations [27] are required for translation into our kernel language. However, these methods are not perfect. For example, array elements can be aliased by indexing accesses, which means we might not be fully knowledgeable about all modes in an array. Furthermore, without good general ....

.... contaminate the remainder of the program (to date, no mode analyzers do the sort of aliasing analysis required to effectively control this contamination) Another point is that a certain class of automatic mode analyzers require language restrictions based on the concept of permissible modes [26, 32]. Sundararajan [26] defines a static analysis technique for determining a minimal set of permissible modes for a Prolog program. This is complicated by the lack of restrictions on Prolog unification. As discussed earlier, committed choice languages restrict unification to ask and tell, making mode ....

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K. Ueda and M. Morita. Moded Flat GHC and Its Message-Oriented Implementation Technique. New Generation Computing, May 1994.

....programs, including committed choice programs, no syntactic distinction is made between variables and their subterms which have output mode and are thus being bound in an occurrence, and those which have input mode and are thus being read in an occurrence. Thus, some form of mode analysis (e.g. [28, 31]) or mode declarations [26] are required for translation into the kernel language. However, these methods are not perfect. For example, array elements can be aliased by indexing accesses, which means we might not be fully knowledgeable about all modes in an array. Furthermore, without good general ....

.... contaminate the remainder of the program (to date, no mode analyzers do the sort of aliasing analysis required to effectively control this contamination) Another point is that a certain class of automatic mode analyzers require language restrictions based on the concept of permissible modes [31, 25]. Sundararajan [25] defines a static analysis technique for determining a minimal set of permissible modes for a Prolog program. This is complicated by the lack of restrictions on Prolog unification. As discussed earlier, committed choice languages restrict unification to ask and tell, making mode ....

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K. Ueda and M. Morita. Moded Flat GHC and Its Message-Oriented Implementation Technique. New Generation Computing, May 1994.

....to programs and queries which generate derivations in which the leftmost atoms is never suspended. In presence of dynamic scheduling this is an important limitation, since if the leftmost atom is suspended then other atoms can be selected. Another related paper is the one by Ueda and Morita [34] which introduces a mode system for the language Flat GHC (also called FGHC and defined by Ueda in [33] However, the scope of the modes in [34] is disjoint from ours since they were devised in order to prove safety of unification for FGHC rather than deadlock freedom. The basic result in [34] ....

....is an important limitation, since if the leftmost atom is suspended then other atoms can be selected. Another related paper is the one by Ueda and Morita [34] which introduces a mode system for the language Flat GHC (also called FGHC and defined by Ueda in [33] However, the scope of the modes in [34] is disjoint from ours since they were devised in order to prove safety of unification for FGHC rather than deadlock freedom. The basic result in [34] shows that a well moded query evaluated in an well moded program does not cause a unification failure. This result is not suitable to prove ....

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K. Ueda and M. Morita. Moded flat ghc and its message-oriented implementation technique. New Generation Computing, 13(1):3--43, 1994.

....on a transition system. The new operational semantics based on calculus can be used for specifying new built in predicates and provides a theoretical foundation for transforming programs to make execution more efficient. 2 Preliminaries 2. 1 Moded FGHC This section briefly reviews moded FGHC [10], which is FGHC with mode information. In moded FGHC every occurrence of a variable is associated with a mode, either in or out. A logical variable is considered a one to n (n 0) communication channel that connects its occurrences. Roughly, occurrences moded in and out correspond to inlets and ....

....occurrences moded in and out correspond to inlets and outlets of information. All variables in a well moded program are guaranteed to be used for oneto n (n 0) communication; that is, for each variable there is one out occurrence and there are n in occurrences. Some advantages of well moded FGHC [10] can be stated informally as follows: ffl Since each variable has one writer, active unification never fails. ffl Given a well moding of a program and a goal, if the goal is reduced by one step the reduced goal and the program have the same well moding. ffl Given a well moding of a program and ....

K. Ueda and M. Morita. Moded Flat GHC and Its Message-Oriented Implementation Technique. to appear in New Generation Computing, OHMSHA, LTD. (1994).

....theorem does not hold any more (see [4] However, the corresponding theorem to Corollary 4.3 still holds. 8 Related Work Formal static analysis methods proposed so far for concurrent languages have been very limited. Although several work has been done on I O mode checking inference[10] 7][18], as far as the authors know, only Nielson s techniques[9] 8] for Concurrent ML[12] can analyze more useful information such as the number of input output operations performed. However, Nielson s method for accumulating effects seems much closer to the traditional one for effect analysis of ....

Ueda, K., and M. Morita, "Moded Flat GHC and Its Message-Oriented Implementation Technique," New Generation Computing, vol. 36, no. 3, pp. 3--43, 1994.

....This paper proposes a framework of automated debugging of program errors under static, constraint based systems for program analysis, and shows how and why program errors can be fixed in the absence of programmers declarations. The language we are particularly interested in is Moded Flat GHC [7][8] proposed in 1990. Moded Flat GHC is a concurrent logic (and consequently, a concurrent constraint) language with a constraint based mode system designed by one of the authors, where modes prescribe the information flow that may be caused by the execution of a program. Supported in part by the ....

....satisfaction problem. Without mode declarations or other kinds of program specification given by programmers, mode reconstruction statically determines the read write capabilities of variable occurrences and establishes the consistency of communication protocols between concurrent processes [8]. The constraint satisfaction problem can be solved mostly (though not entirely) as a unification problem over feature graphs (feature structures with cycles) and can be solved in almost linear time with respect to the size of the program [1] As we will see later, types also can be reconstructed ....

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Ueda, K. and Morita, M., Moded Flat GHC and Its Message-Oriented Implementation Technique. New Generation Computing, Vol. 13, No. 1 (1994), pp. 3--43.

....that the arguments of the structure are initialized to 0 rather than fresh, distinct variables. This is because we have found that initializing its elements to a filler constant and replacing them using setarg 5 shows much better a#nity with a static mode system that plays various important roles [30] in concurrent logic programming. As discussed in [31] strong moding is deeply concerned with the number of access paths (or references) to each variable (or its value) It prefers variables with exactly two occurrences to those with three or more occurrences by giving the former more generic, ....

Ueda, K. and Morita, M., Moded Flat GHC and Its Message-Oriented Implementation Technique. New Generation Computing, Vol. 13, No. 1 (1994), pp. 3--43.

....the other, prefixed form, atomic tell, in this paper. Since eventual tell simply adds a new constraint to the store, the store can become inconsistent when an attempt is made to equate a variable to two di#erent values. This can be avoided by using a non standard type system, called a mode system [41], that controls the number of write capabilities of each variable in the system. The advocation of eventual tell apparently motivated Honda and Tokoro s asynchronous # calculus [15] 2. Polyadic. Concurrent logic programming incorporated (rather than devised) well understood built in data ....

....of the clause. There is rather small di#erence between message passing of the asynchronous # calculus and message passing by unification, as long as only one process holds a write capability and use it once. These conditions can be statically checked in well moded concurrent logic programs [41] and in the # calculus with a linear type system [19] When two processes communicate repeatedly, constraintbased concurrency uses streams because one fresh logical variable must be prepared for each message passing, while in the linear # calculus the same channel could be recycled as suggested in ....

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Ueda, K. and Morita, M., Moded Flat GHC and Its Message-Oriented Implementation Technique. New Generation Computing, Vol. 13, No. 1 (1994), pp. 3--43.

....X 0 ( 0) and 5, should become identical. 6 Mode System for Flat GHC To guarantee the security of unification statically, a mode system for Flat GHC was designed in 1990 [12] This and subsequent sections will introduce it rather informally but from various aspects. We refer the readers to [15] for the precise and detailed description. As a metaphor, consider two electric devices connected by a cable for conveying signals. The cable may have a structure such as an array of wires. As the nature of a cable, its both ends, viewed from outside the cable, should have opposite polarity ....

...., without causing the failure of the extended occur check. Then all the variables in Q are instantiated to ground (i.e. variable free) terms. This theorem says that if the termination of Q can be proved, the groundness property comes for free. The proofs of all the above results can be found in [15]. 8 Implication of the Mode System The mode system of Flat GHC has been exhibiting a vast influence on programming, implementation, and language design. 8.1 Programming Introducing a mode system means to subset a language, but we have felt almost no loss of expressive power. The mode system can ....

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Ueda, K. and Morita, M., Moded Flat GHC and Its Message-Oriented Implementation Technique. New Generation Computing, Vol. 13, No. 1 (1994), pp. 3--43.

....concurrent logic programming in which logical (or single assignment) variables are used as communication channels, and proposes a theoretical framework, called linearity analysis, that distinguishes between one to one and one to many communcation. We are particularly interested in Moded Flat GHC, [8] a concurrent logic language with strong moding, because its mode system infers information flow of logical variables and simplifies linearity analysis. We have found, from concurrent logic programs written so far, that most logical variables are used for one to one communication. 10] In ....

....substitution # such that g = h#, and Q # = Q g # B#, where and # are multiset di#erence and union, respectively. Reduction of a unification goal (t 1 = t 2 ) # Q: Q # = Q (t 1 = t 2 ) #, where # is the most general unifier of t 1 and t 2 . We assume that the program is wellmoded, [8] in which case the unification does not fail except due to occur check. In either case, reduction in general involves the rewriting of a variable (say v) to a term t (#= v) In the reduction of a non unification goal, v must be a variable in the (renamed) program clause, while in the reduction of ....

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Ueda, K. and Morita, M., Moded Flat GHC and Its Message-Oriented Implementation Technique. New Generation Computing, Vol. 13, No. 1 (1994), pp. 3--43.

....The framework was then implemented in Kima, an automated error correction system for concurrent logic programs, which featured several improvements to make the system more practical and efficient. The mechanism of error correction in Kima is based on the mode and type system of Moded Flat GHC [8][9]. Moded Flat GHC is a concurrent logic (and consequently, a concurrent constraint) language with a constraint based mode system designed by one of the authors. Languages equipped with strong typ 2 ing or strong moding 1 enable the detection of type mode errors by checking or reconstructing ....

....GHC allows us to solve a set of mode constraints obtained from program text as a constraint satisfaction problem. Mode reconstruction statically determines the read write capabilities of variable occurrences and establishes the consistency of communication protocols between concurrent processes [9]. As we will see later, types in Moded Flat GHC also can be reconstructed using a similar (and simpler) technique. When a concurrent logic program contains bugs, it is very likely that mode constraints obtained from the erroneous symbol occurrences are incompatible with the other constraints. We ....

[Article contains additional citation context not shown here]

Ueda, K. and Morita, M., Moded Flat GHC and Its Message-Oriented Implementation Technique. New Generation Computing, Vol. 13, No. 1 (1994), pp. 3--43.

....The framework was then implemented in Kima, an automated error correction system for concurrent logic programs, which featured several improvements to make the system more practical and e#cient. The mechanism of error correction in Kima is based on the mode and type system of Moded Flat GHC [8][9]. Moded Flat GHC is a concurrent logic (and consequently, a concurrent constraint) language with a constraint based mode system designed by one of the authors. Languages equipped with strong typing or strong moding 1 enable the detection of type mode errors by checking or 1 Modes can be thought ....

....GHC allows us to solve a set of mode constraints obtained from program text as a constraint satisfaction problem. Mode reconstruction statically determines the read write capabilities of variable occurrences and establishes the consistency of communication protocols between concurrent processes [9]. As we will see later, types in Moded Flat GHC also can be reconstructed using a similar (and simpler) technique. When a concurrent logic program contains bugs, it is very likely that mode constraints obtained from the erroneous symbol occurrences are incompatible with the other constraints. We ....

[Article contains additional citation context not shown here]

Ueda, K. and Morita, M., Moded Flat GHC and Its Message-Oriented Implementation Technique. New Generation Computing, Vol. 13, No. 1 (1994), pp. 3--43.

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Kazunori Ueda and Masao Morita. Moded flat GHC and its message-oriented implementation technique. New Generation Computing, 13(1):3--43, 1994.

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K. Ueda and M. Morita. Moded flat GHC and its message-oriented implementation technique. New Generation Computing, 13(1):3--43, 1994.

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