LL(k) grammars are grammars that can be parsed from left-to-right, creating a leftmost derivation, using k tokens of lookahead.
Questions tagged [ll-grammar]
209 questions
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PEGjs grammar star (*) not matching as expected
I have this lexeme:
a().length()
And this PEGjs grammar:
start = func_call
func_call = header "(" ")"
header = "a" suffix*
suffix = "(" ")" ("." "length")
In the grammar, I'm parsing a function call. This currently parses, as you can try online…
Andy Ray
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How to disprove grammar of being LL(3)?
I have the following grammar I made up:
S -> a a a t | a a a a
I'm trying to prove that it's not LL(3). I found that First(S)={a} and Follow(S)={$} but I can't seem to figure out what I need to do to disprove it being LL(3). It's a small grammar I…
vesii
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Calculating First and Follow of a grammar
I'm trying to calculate First and Follow of the following grammar:
S -> A B C D E
A -> a
A -> EPSILON
B -> b
B -> EPSILON
C -> c
D -> d
D -> EPSILON
E -> e
E -> EPSILON
I calculated them and got First(S)={a,b,c}. But using this tools, says:…
vesii
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How does FOLLOW work for the following CFG?
The original cfg is
S -> S + S | SS | (S) | S* | a
After refactoring and eliminating left recursion, I arrive at the following reduction:
S -> TB
B -> AB | e
A -> +S | TB | *
T -> (S) | a
When calculating follow(B), online sources that I can find…
Alexander Brassel
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Turn a particular grammar into LL 1 grammar
Suppose we have the following CFG:
A → Bd
B → dA|a|ɛ
Now if I try to calculate FIRST and FOLLOW sets, I think I can get it done as follows:
First(A) = { d, a }
First(B) = { d, a, ɛ }
FOLLOW(A) = { d, $ }
FOLLOW(B) = { d }
And the parser table…
M0B
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1 answer
How to solve "The following sets of rules are mutually left-recursive" ANTLR error
The following sets of rules are mutually left-recursive
[valeurBooleene, valeur]
I know that ANTLR handle well left-recursive rules but only in one rule, not between rules.
I have to rewrite my rules to solve the mutually left-recursive problem…
Aubin
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How do you construct a parse tree during LL(1) parsing?
I was wondering if there is a way to construct a parse tree during LL(1) parsing. I've been trying for days, but have been unable to find a solution. This question is similar, but it doesn't provide enough implementation details, and it is for the…
xilpex
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Unable calculate to get follow set
I've been trying to calculate the follow set of a grammar for some time now, and have run into yet another problem. Here is my follow set calculator:
def gen_follow_set(grammar, start_sym, first_sets):
follow_sets = {nterm: set() for nterm in…
xilpex
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0 answers
Why is this grammar not LL(1)?
I am doing some homework, and was asked to show that the grammar A -> aAa | ε is not LL(1). From everything that I have seen, the answer I have so far is that since the First and the Follow sets of A contain a. Is this correct or am I thinking about…
user29451
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Not able to find first() and follow() for non LR grammer
I have removed left recursion from the given grammar. But, now I have to find out first and follow to create a parse table.
Original :
S -> aSb | bSa | SS | epsilon
New: After removing left recursion :
S -> aSbSS' | bSaSS' | S' and
…
P H
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how to resolve FIRST-FOLLOW conflict in rule with right recursion
I have a grammar that looks like this
G = ({A, B, C},{a, c},P, A),
P = {
1. A → BaC,
2. B → aB
3. B → ε,
4. C→c
}
and I want to resolve the FIRST(2.) = {a} FOLLOW(B) = {a} conflict. But with every attempt I fail because I am not able to use the…
eja08
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LL(1) parser conflict when parsing C language BNF
I'v calculated all the first sets of each production according to https://cs.wmich.edu/~gupta/teaching/cs4850/sumII06/The%20syntax%20of%20C%20in%20Backus-Naur%20form.htm, but I found the first sets is highly conflicted.
For example, code like…
user2269707
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1 answer
making a grammar ll(1) and unambiguous
I have a CFG in the form
PB := PB | R | R
R := s
I have tried to make it ll(1) by removing the left recursion resulting in
PB := R PB' | R PB'
PB' := PB'| ϵ
R := s
However, I believe, removing the left recursion is making the grammar now…
Kneelac
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Tokenize abstract terminals in LL grammar
I am currently writing a basic parser for an XML flavor. As an exercise, I am implementing an LL table-driven parser.
This is my example of BNF grammar:
%token name data string
%% /* LL(1) */
doc : elem
elem : "<"…
explogx
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How Do I left factor and eliminate left recursion?
My Production rules are as follows:
S → id = Exp
S → id (Arglist)
Arglist → Arglist , Exp
Arglist → Exp
Exp → id (Arglist)
Exp → id
This is my first attempt:
S -> id S'
S' -> ϵ | = EXP | (Arglist)
Arglist -> Arglist'
Arglist' -> ϵ | ,Exp…
webchatowner
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