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- LL_grammar abstract "In formal language theory, an LL grammar is a formal grammar that can be parsed by an LL parser, which parses the input from Left to right, and constructs a Leftmost derivation of the sentence (hence LL, compared with LR parser that constructs a rightmost derivation). A language that has an LL grammar is known as an LL language. These form subsets of deterministic context-free grammars (DCFGs) and deterministic context-free languages (DCFLs), respectively. One says that a given grammar or language "is an LL grammar/language" or simply "is LL" to indicate that it is in this class.There is a separate LL(k) parser for each natural number k (0, 1, 2, ...) – an LL parser is called an LL(k) parser if it uses k tokens of lookahead when parsing a sentence – and there are accordingly the subsets of LL(k) grammars for each k (LL(0) grammars, LL(1) grammars, etc.) and corresponding subsets of LL(k) languages. As allowing more tokens of lookahead makes the parser strictly more powerful – there are LL(k + n) languages that are not LL(k) languages – these form strictly increasing sequence of sets, LL(0) ⊊ LL(1) ⊊ LL(2) ⊊ …. Since these are all DCFLs, a corollary is that for any fixed k, there are DCFLs that are not LL(k).An LL parser is called an LL(*) parser if it is not restricted to a finite k tokens of lookahead, but can make parsing decisions by recognizing whether the following tokens belong to a regular language (for example by use of a Deterministic Finite Automaton), and accordingly there are the set of LL(*) grammars and the set of LL(*) languages.[citation needed]LL grammars, particularly LL(1) grammars, are of great practical interest, as they are easy to parse, either by LL parsers or by recursive descent parsers, and many computer languages are designed to be LL(1) for this reason. However, the limitations of LL parsers mean that languages that can be expressed by LL grammars are limited. Further, even if a language can be expressed by an LL grammar, or LL(k) for a given k, the grammar is generally longer and more complicated than an alternative grammar using more expressive rules so that the grammar is not LL(k) – either requiring more tokens of lookahead or not being LL at all. Being in LL(k) is a property of the grammar as a whole, not of individual production rules, but there are some production rules – notably those using left recursion – which cannot be presented in an LL(k) grammar.LL(1) grammars are very popular because the corresponding LL parsers only need to look at the next token to make their parsing decisions. Languages based on grammars with a high value of k have traditionally been considered[citation needed] to be difficult to parse, although this is less true now given the availability and widespread use[citation needed] of parser generators supporting LL(k) grammars for arbitrary k.LL parsers are table-based parsers, similar to LR parsers. LL grammars can alternatively be characterized as precisely those that can be parsed by a predictive parser – a recursive descent parser without backtracking – and these can be readily written by hand. This article is about the formal properties of LL grammars; for parsing, see LL parser or recursive descent parser.".
- LL_grammar wikiPageID "32095640".
- LL_grammar wikiPageRevisionID "602865857".
- LL_grammar subject Category:Formal_languages.
- LL_grammar comment "In formal language theory, an LL grammar is a formal grammar that can be parsed by an LL parser, which parses the input from Left to right, and constructs a Leftmost derivation of the sentence (hence LL, compared with LR parser that constructs a rightmost derivation). A language that has an LL grammar is known as an LL language. These form subsets of deterministic context-free grammars (DCFGs) and deterministic context-free languages (DCFLs), respectively.".
- LL_grammar label "LL grammar".
- LL_grammar sameAs m.0wzx55w.
- LL_grammar sameAs Q16249519.
- LL_grammar sameAs Q16249519.
- LL_grammar wasDerivedFrom LL_grammar?oldid=602865857.
- LL_grammar isPrimaryTopicOf LL_grammar.