In formal language theory, a context-free grammar (CFG) is a grammar subject to a special constraint: that the left-hand side (LHS) consist of a single non-terminal symbol. CFGs are capable of representing the set of context-free languages (CFLs).
Questions tagged [context-free-grammar]
1364 questions
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how to find context free grammar when ac elements have another element b in between
I am trying to find the context free grammar for this equation
L = {a ᶦ b ʲ c ᵏ | i = j or i = k, i, j, k ≥ 0}
I have been able to work out the grammar for when a and b have equal exponent
such as
S->ɛ
S->XY
S->ab
S->aXb
Y->cY | ɛ
but I am having…
giacomo venturelli
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Does aabbabb belong to the regular expression ((a*| b*)bb)*?
I'm just curious if ((a*| b*)bb)* means that whatever number of a's or b's used in the inner parentheses must be fixed. Like if I had aabb, I could not follow it with a different number of a's?
`
Would something like abbaabb or a bbbabb or bbbaaabb…
Shisui
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converting CFG to regular expression
Here's a CFG that generates strings of 0s, 1s, or 0s and 1s arranged like this (001, 011) where one of the characters must have a bigger count than the other like in 00011111 or 00000111 for example.
S → 0S1 | 0A | 0 | 1B | 1
A → 0A | 0
B → 1B |…
Sieg
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Write grammar for context-free language
I need to find the grammar for the following language:
L = {a^n w w^R b^n; n >= 1, w є {a,b} and w^R is the reverse of w}
I'm really stuck on what "w є {a,b}" and "reverse of w" means.
Could someone explain this to me?
davai
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Context free grammar for L{a^n b^m c^t where t>0,m>0,n>2}
For a context free grammar for L{a^n b^m c^t where t>0,m>0,n>2}
S -> ABC
A ->aB|a
B ->bB|b
C ->cC|c
Is this correct?
hammad ashraf
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ANTLR4 CPP14 Grammar not able to identify decimal numbers
I am using the below ANTLR grammar for parsing my code.
https://github.com/antlr/grammars-v4/tree/master/cpp
The following code gives error while parsing. Here "08" is not identifying as an integer literal.
TEST_F(suite_name_test_p, 08)
{
…
Anand
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What are the words recognized by the CFG S - > 1 | S 0
I am dealing with this exercise: What are the words of
S - > 1 | S 0
I find the problem particularly challenging because there are so many combinations and I have no clue these how to exhaustively enumerate all possibilities. As a starter, the…
zell
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What makes this example a context-free language rather than regular language?
I'm having trouble seeing what makes "any number of a's followed by the same number of b's and c's" a context-free language, while "any number of a's followed by any number of b's followed by any number of c's" is a regular language, as I saw…
sonder
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How to remove left recursion from A -> Aα | ε
I think the left-recursion for this grammar is not removable. Correct me if I am wrong.
α is Alpha that is a Non-terminal
ε is Epsilon.
HamzaFarooq
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How to solve shift/reduce conflict using operator precedence?
So I have this grammar I'm trying to build an LR(1) table for
E' -> E
E -> E + E
E -> E * E
E -> ( E )
E -> a
So far, this my table
I'm trying to solve the conflicts here. I thought about changing the grammar to…
Ruba Sbeih
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How do i check the ambiguity in this grammar:-
E->EE+/E(E)/id
Check if the given grammar is ambiguous. Also, it would be of a great help if you could tell me the process to remove the ambiguity.
I tried making the parse tree for it but could not figure out how to actually make it to find an…
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Formal grammar to express inner join
I have a language that describe a domain by predicates of arbitrary arity.
For example, in first-order logic I can write the following rule:
PersonlivesInCountry(x,y) <-> person(x), PersonlivesInState(x,z), StateisInCountry(z,y)
In this exampple,…
Wall
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Is creating a context-free-grammar parser easy?
Is creating a context-free-grammar parser easy? Can they be created automatically via generators? Are there any paper about this topic?
Bighted19
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What is wrong with this grammar?
Getting this error. I'm pasting a part of the error and grammar rules.
parser.y: warning: 6 nonterminals useless in grammar [-Wother]
parser.y: warning: 15 rules useless in grammar [-Wother]
parser.y:95.1-16: warning: nonterminal useless in…
afsara_ben
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Context free grammar for a language
How would I go about writing a context free grammar for the following language:
{a^x b^y c^z | x >= 0, y >= 0, z >= 0, y = x + z}
user8967903
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