218:, have similar methods and parsing tables; their main difference is in the mathematical grammar analysis algorithm used by the parser generation tool. LALR generators accept more grammars than do SLR generators, but fewer grammars than full LR(1). Full LR involves much larger parse tables and is avoided unless clearly needed for some particular computer language. Real computer languages can often be expressed as LALR(1) grammars. In cases where they can't, a LALR(2) grammar is usually adequate. If the parser generator allows only LALR(1) grammars, the parser typically calls some hand-written code whenever it encounters constructs needing extended lookahead.
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sets as lookahead sets which associate the right hand side of a LR(0) core to a lookahead terminal. This is a greater simplification than that in the case of LALR because many conflicts may arise from LR(0) cores sharing the same right hand side and lookahead terminal, conflicts which are not present
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and
Canonical LR parser generator, an LALR parser generator constructs the LR(0) state machine first and then computes the lookahead sets for all rules in the grammar, checking for ambiguity. The Canonical LR constructs full lookahead sets. LALR uses merge sets, that is it merges lookahead sets where
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In practice, LALR offers a good solution, because LALR(1) grammars are more powerful than SLR(1), and can parse most practical LL(1) grammars. LR(1) grammars are more powerful than LALR(1), but ("canonical") LR(1) parsers can be extremely large in size and are considered not practical. Minimal
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generators. What differentiates one from another is the type of CFG which they are capable of accepting and the type of parsing algorithm which is used in the generated parser. An LALR parser generator accepts an LALR grammar as input and generates a parser that uses an LALR parsing algorithm
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in 1975 at AT&T Labs. Another, "TWS", was created by Frank DeRemer and Tom
Pennello. Today, there are many LALR parser generators available, many inspired by and largely compatible with the original Yacc, for example
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Frank DeRemer invented LALR parsers with his PhD dissertation, called "Practical LR(k) Translators", in 1969, at MIT. This was an important breakthrough, because LR(k) translators, as defined by
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in LALR. This is why SLR has less language recognition power than LALR with
Canonical LR being stronger than both since it does not include any simplifications.
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in his 1965 paper, "On the
Translation of Languages from Left to Right", were much too large for implementation on computer systems in the 1960s and 70's.
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are desirable because they are very fast and small in comparison to other types of parsers.
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Efficient
Computation Of LALR(1) Look-Ahead Sets, DeRemer and Pennello, TOPLAS (1982)
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An early LALR parser generator and probably the most popular one for many years was "
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Comparison of deterministic context-free language parser generators
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LR(1) parsers are small in size and comparable to LALR(1) parsers.
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The LALR parser and its alternatives, the SLR parser and the
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46:. Unsourced material may be challenged and removed.
285:Alfred V. Aho, Ravi Sethi, and Jeffrey D. Ullman.
130:which is capable of parsing files written in the
189:" (Yet Another Compiler Compiler), created by
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308:– available freely from the author's page at
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288:Compilers: Principles, Techniques, and Tools
265:. AT&T Bell Laboratories. Archived from
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350:Practical Translators for LR(k) languages
226:the LR(0) core is the same. The SLR uses
166:(which is driven by LALR parser tables).
106:Learn how and when to remove this message
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263:"Yacc: Yet Another Compiler-Compiler"
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120:lookahead LR parser (LALR) generator
44:adding citations to reliable sources
301:Understanding and Writing Compilers
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621:History of compiler construction
122:is a software tool that reads a
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626:Comparison of parser generators
241:Comparison of parser generators
31:needs additional citations for
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347:DeRemer, Franklin L. (1969).
340:10.1016/S0019-9958(65)90426-2
198:, a pun on the original Yacc/
356:(Ph.D.). MIT. Archived from
291:Addison—Wesley, 1986. (AKA
631:Operator-precedence grammar
306:in English, not mathematics
261:Stephen C. Johnson (1975).
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206:for a more detailed list.
141:There are other types of
574:Definite clause grammar
328:Information and Control
55:"LALR parser generator"
579:Deterministic parsing
134:defined by the CFG.
132:context-free language
126:(CFG) and creates an
124:context-free grammar
40:improve this article
616:Scannerless parsing
584:Dynamic programming
216:Canonical LR parser
412:Parsing algorithms
652:Parser generators
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438:Recursive descent
143:parser generators
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363:on 2013-08-19
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531:Mixed, other
522:Shift-reduce
365:. Retrieved
358:the original
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324:Knuth, D. E.
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271:. Retrieved
267:the original
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180:Donald Knuth
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136:LALR parsers
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38:Please help
33:verification
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589:Memoization
554:Statistical
548:Left corner
505:Generalized
462:Precedence
128:LALR parser
96:August 2011
606:Parse tree
538:Combinator
495:Look-ahead
367:2013-08-19
273:2012-07-02
248:References
223:SLR parser
163:GLL parser
155:GLR parser
145:, such as
66:newspapers
500:Canonical
455:Bottom-up
196:GNU bison
159:LL parser
151:LR parser
646:Category
471:Operator
420:Top-down
235:See also
210:Overview
174:History
80:scholar
490:Simple
466:Simple
428:Earley
228:FOLLOW
202:. See
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543:Chart
361:(PDF)
354:(PDF)
87:JSTOR
73:books
599:LALR
187:yacc
161:and
59:news
611:AST
569:PEG
512:CYK
336:doi
200:Yak
42:by
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485:LR
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