LR(k) grammars are grammars that can be parsed bottom-up from the left-to-right, producing a rightmost derivation, using k tokens of lookahead. LR(k) parsers are among the most powerful deterministic parsers available, but are often too large to use in practice.
Questions tagged [lr-grammar]
178 questions
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How does gcc/clang parse c++ if it can't be parsed by a LR(1) parser?
GCC/Clang are handwritten parsers. I read a post saying that C++ can't be parsed by an LR(1) parser (Why can't C++ be parsed with a LR(1) parser?). If so, how come GCC/Clang are handwritten recursive descent parsers, when LR(1) is more powerful than…
xilpex
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LR(1) parser - Making inline productions
How would you implement inline productions in an LR(1) parser? By inline productions I mean the production is there, but only for parsing-- it won't get generated in the parse tree/AST. How would I implement this? I have a list of inline…
xilpex
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LR parser for epsilon
I've recently implemented an LR(1) parser (without epsilon), and have been wondering how I would implement epsilon in the parsing algorithm (note: not the table construction algorithm). This is my grammar:
start -> A b
b -> B | \epsilon
I've…
xilpex
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LR Parsing for arithmetic expressions
I have got LR grammar and LR table for expressions like (1+1),1+(a+1)
0: E’->E
1: E ->E + T
2: E-> T
3: T ->T * F
4: T-> F
5: F ->( E )
6: F-> id
string[,] ActionTable =
//+ * ( ) id end E T F
{
…
azh
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How do I check if grammar is SLR(1)?
How do I check if this grammar is SLR(1)?
S' -> S
S -> [ B
A -> int
A -> [ B
B -> ]
B -> C
C -> A ]
C -> A , C
First I've created it's automaton, then computed the follow sets for non-terminals and then created the…
Octavian
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How can LR parsers generate parse trees?
Suppose I have a grammar:
S -> Aaa
A -> a | ε
Clearly, this grammar can parse only sequences aa and aaa. A simple LR(1) parser (or even LL) can parse these when transformed into an equivalent grammar:
S -> aaA
A -> a | ε
Although these grammars…
Dennis
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How easy is to find a string that leads to conflict in a SLR(1) parser compared to a LR(1)
It is known that SLR(1) parsers usually have less states than LR(1). But is it easier or harder because of this to find a string that leads to conflict in a SLR(1) parser compared to a LR(1) and why?
Thank you in advance.
Dragonite LvL 100
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How to calculate expression result using LR parser in C
I am writing a program for calculating the expression value using LR parser (2 stack-track). The code is working fine for single digits. It adds or multiplies two integers from 0-9 but for double digits like 12+5*10 it fails. The code is below. I…
Ammar Ul Hassan
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Is these 2 grammars equal?
I have the following grammar which is ambiguous and of course not slr1:
E -> E+A+A | E+A-A | E-A+A | E-A-A | T
T -> T+A | T-A | A
A -> A*B | A/B | B
B -> (E) | x
I used the rule of transformation which is:
E -> E + T -----> E -> TE'
…
Kostas Ayfantop
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solving the shift/reduce conflict
I am currently having the following grammar which I am asked if it is SLR(1) or not. The grammar is:
E -> E + A + A | E - A + A | E + A - A | E - A - A | T .
T -> T + A | T - A | A .
A -> A * B | A / B | B .
B -> ( E ) | x .
The grammar is…
Kostas Ayfantop
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2 answers
LR(1) BNF grammar for function parameters with trailing elipsis
I would like to write an LR(1) grammar in BNF form for the language described by these two rules from The Complete Syntax of Lua:
parlist ::= namelist [`,´ `...´] | `...´
namelist ::= Name {`,´ Name}
I have tried the following grammars, but…
user200783
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Finding an equivalent LR grammar for the same number of "a" and "b" grammar?
I can't seem to find an equivalent LR grammar for:
S → aSbS | bSaS | ε
which I think recognize strings with the same number of 'a' than 'b'.
What would be a workaround for this? Is it possible to find and LR grammar for this?
Thanks in…
DarK_FirefoX
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Why are the only the states 0 and 2 present in line 8?
LR Parsing:
LR Parsing Table:
In line 7, we reduce by T->T*F.
And State 7 on T does not have any transition.
In line 8, why do we have only the states 0 and 2?
Ujjayanta Bhaumik
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How can I eliminate shift-reduce conflicts by the same operator
I intended to use bison to parse some scripting language, in this language I can write code like the following:
a = input()
b = a + 1
function myfunc
a = input()
b = a + 1
end function
I found that the block
a = input()
b = a + 1
which…
calvin
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Look ahead in LR(1) parsing
I have some problem to understand how to make look ahead in LR(1). I've already found this question about the same problem LR(1) - Items, Look Ahead but this don't help me.
S'->.S,$
S->.L=R,$
S->.R,$
L->.*R,=/$
L->.id,=/$
R->.L,$
I understand the…
JEricaM
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