共查询到19条相似文献,搜索用时 437 毫秒
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本文将案例法引入了《编译原理》课程的教学,发挥案例法的优势,以二义文法为主线,探讨了二义文法和递归文法、LL(1)文法、LR(0)文法和SLR(1)文法的关系,找出了一些判定文法有无二义性的充分条件,同时研究了解决二义性的方法,加深了学生对二义文法的理解。 相似文献
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本文先简要介绍了一种上下文无关文法的推断方法--逐步求精法,然后论述了递归概念在文法推断中的核心作用,并从递归概念的特殊性质出发提出了多条启发规则,能有效减少无效探求和与用户交互的次数,尤其适合于文法较复杂、例句集信息量较大的情况。这些启发规则同时也适用于对上下文无关文法的其它推断方法。 相似文献
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本文将模糊树自动机和模糊上下文无关树文法的概念推广到格半群上。证明了在接受语言和生成语言的意义下,树自动机和上下文无关树文法是等价的。同时给出了构造正规形式的等价文法的方法。 相似文献
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用状态转换图分析正规式时需要考虑的情况比较多,容易造成疏漏。且这种方法需要递归进行,多次扫描正规式,效率不高。该文采用SLR分析加属性文法只需一遍扫描就可以将正规式转存为NFA,效率要高得多。 相似文献
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提出了量子上下文无关文法(l-VCFG)的概念,并研究了其具有的代数性质;证明了量子上下文无关文法(l-VCFG)和Chomsky范式文法(l-VCNF)以及Greibach范式文法(l-VGNF)的相互等价性;详细研究了量子上下文无关语言的代数刻画以及对于正则运算的封闭性。 相似文献
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一、前言LR分析算法是knuth 1965年首先提出的.LR分析器能自动生成,运行效率高,查错功能强,识别语法类大,可用于大多数由上下文无关文法描述的程序语言.然而,由于一般的LR分析器状态数量极多,需要大量的存储空间,很不实用.为此,人们做了许多努力.以后演变出的SLR、LALR文法都是对LR文法加以某种限制,所识别的文法类是LR文法的一个子集,因此可以比较有效地实现. 相似文献
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本文提出了可交换上下文无关文法及其该文法产生的语言——可交换上下文无关语言,证明了正规语言类是可交换上下文无关语言类的一个子集,而可交换上下文无关语言类是上下文无关语言类的一个子集;讨论了可交换上下文无关语言的结构特点,并给出了可交换上下文无关语言的Pumping引理。 相似文献
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提出了推导可交换上下文无关语言及其文法,证明了正规语言类和有界上下文无关语言类都是推导可交换上下文无关语言类的子集,而推导可交换上下文无关语言类是上下文无关语言类的一个子集;定义了该类语言的α闭包等有关运算,给出了推导可交换上下文无关语言表达式,证明了推导可交换上下文无关文法、推导可交换上下文无关语言表达式之间的等价转换. 相似文献
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《国际计算机数学杂志》2012,89(4):251-269
This paper deals with the concepts of a matrix form and strict interpretation. By a matrix form we mean a context-free matrix grammar. Via an interpretation mechanism it generates a family of structurally related grammars and these generate a family of languages. We study here the properties of matrix forms as generators for the families of regular, linear and context-free languages. It is for instance shown that an arbitrary matrix form with only one nonterminal symbol does not generate the family of context-free languages if it contains a matrix with at least two productions. 相似文献
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《国际计算机数学杂志》2012,89(3-4):159-180
We investigate context-free grammars the rules of which can be used in a productive and in a reductive fashion, while the application of these rules is controlled by a regular language. We distinguish several modes of derivation for this kind of grammar. The resulting language families (properly) extend the family of context-free languages. We establish some closure properties of these language families and some grammatical transformations which yield a few normal forms for this type of grammar. Finally, we consider some special cases (viz. the context-free grammar is linear or left-linear), and generalizations, in particular, the use of arbitrary rather than regular control languages. 相似文献
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Augusto Celentano 《Computer Languages, Systems and Structures》1981,6(2):95-107
Extended context-free grammars allow regular expressions to appear in productions right hand sides, and are a clear and natural way to describe the syntax of programming languages.In this paper an LR parsing technique for extended context-free grammars is presented, which is based on an underlying transformation of the grammar into an equivalent context-free one.The technique is suitable for inclusion in one-pass compilers: the implementation requires little extensions to the algorithms working for normal LR grammars. Besides describing the parsing method, the paper shows also the algorithms for deriving the parsing tables; tables optimization is also discussed. Finally, this technique is compared with other proposals appeared in the literature. 相似文献
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Javier Esparza Stefan Kiefer Michael Luttenberger 《Information Processing Letters》2011,111(12):614-619
Parikh?s theorem states that the Parikh image of a context-free language is semilinear or, equivalently, that every context-free language has the same Parikh image as some regular language. We present a very simple construction that, given a context-free grammar, produces a finite automaton recognizing such a regular language. 相似文献
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We study abstract interpretations of a fixpoint protoderivation semantics defining the maximal derivations of a transitional semantics of context-free grammars akin to pushdown automata. The result is a hierarchy of bottom-up or top-down semantics refining the classical equational and derivational language semantics and including Knuth grammar problems, classical grammar flow analysis algorithms and parsing algorithms. 相似文献
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Marian Gheorghe 《Formal Aspects of Computing》2000,12(6):459-472
Stream X-machines are a general and powerful computational model. By coupling the control structure of a stream X-machine
with a set of formal grammars a new machine called a generalised stream X-machine with underlying distributed grammars, acting as a translator, is obtained. By introducing this new mechanism a hierarchy of computational models is provided.
If the grammars are of a particular class, say regular or context-free, then finite sets are translated into finite sets,
when ?k, = k derivation strategies are used, and regular or context-free sets, respectively, are obtained for ?k, * and terminal derivation strategies. In both cases, regular or context-free grammars, the regular sets are translated into non-context-free
languages. Moreover, any language accepted by a Turing machine may be written as a translation of a regular set performed
by a generalised stream X-machine with underlying distributed grammars based on context-free rules, under = k derivation strategy. On the other hand the languages generated by some classes of cooperating distributed grammar systems
may be obtained as images of regular sets through some X-machines with underlying distributed grammars. Other relations of
the families of languages computed by generalised stream X-machines with the families of languages generated by cooperating
distributed grammar systems are established. At the end, an example dealing with the specification of a scanner system illustrates
the use of the introduced mechanism as a formal specification model.
Received September 1999 / Accepted in revised form October 2000 相似文献
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Fuzzy context-free max- grammar (or FCFG, for short), as a straightforward extension of context-free grammar, has been introduced to express uncertainty, imprecision, and vagueness in natural language fragments. Li recently proposed the approximation of fuzzy finite automata, which may effectively deal with the practical problems of fuzziness, impreciseness and vagueness. In this paper, we further develop the approximation of fuzzy context-free grammars. In particular, we show that a fuzzy context-free grammar under max- compositional inference can be approximated by some fuzzy context-free grammar under max-min compositional inference with any given accuracy. In addition, some related properties of fuzzy context-free grammars and fuzzy languages generated by them are studied. Finally, the sensitivity of fuzzy context-free grammars is also discussed. 相似文献
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Context-free tree grammars, originally introduced by Rounds [Math. Systems Theory 4(3) (1970) 257–287], are powerful grammar devices for the definition of tree languages. The properties of the class of context-free tree languages have been studied for more than three decades now. Particularly important here is the work by Engelfriet and Schmidt [J. Comput. System Sci. 15(3) (1977) 328–353, 16(1) (1978) 67–99]. In the present paper, we consider a subclass of the class of context-free tree languages, namely the class of linear context-free tree languages. A context-free tree grammar is linear, if no rule permits the copying of subtrees. For this class of linear context-free tree languages we show that the grammar derivation mode, which is very important for the general class of context-free tree languages, is immaterial. The main result we present is the closure of the class of linear context-free tree languages under linear frontier-to-root tree transduction mappings. Two further results are the closure of this class under linear root-to-frontier tree transduction mappings and under intersection with regular tree languages. 相似文献
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