Free Languages (CFL) • The pumping lemma showed there are languages that are not regular – There are many classes “larger” than that of regular languages – One of these classes are called “Context Free” languages • Described by Context-Free Grammars (CFG) – Why named context-...
Context-free Grammars Context-freeGrammars 上下文无关文法 theoryofcomputation 3-1 outline Context-freegrammars(CFG)Context-freelanguages(CFL)ChomskyNormalFormofCFG(CNF)RLCFL theoryofcomputation 3-2 Context-freeGrammars Originatedasabstractmodelfor —Structureofnaturallanguages(Chomsky)...
Some CFL can be generated only by ambiguous grammars. Such languages are called inherently ambiguous.Chomsky Normal FormDefinition A CFG is in Chomsky normal form if every rule is of the formA→BCA→a(4)(5)(4)A→BC(5)A→awhere aa is any terminal and AA, BB, and C are any ...
Block structure was introduced into computerprogramming languagesby theAlgolproject (1957–1960),which, as a consequence, also featured a context-free grammar to describe the resulting Algol syntax. This became a standard feature of computer languages, and the notation for grammars used in concrete d...
context-free grammarscontext-free languagesprocess algebrasimple context-free languagesA context-free grammar (CFG) in Greibach Normal Form coincides, in anothernotation, with a system of guarded recursion equations in Basic Process algebra. Hence, to eachCFG, aprocess can be assigned absolution, ...