Questions tagged [parsers]

Questions about algorithms that decide whether a given string belongs to a fixed formal language.

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Disposition: Parsing

I have to prepare 30 minutes of oral examen about the subject called parsing. Where I have to talk about it. And then I shall hand in like 30 pages (including code and figures etc). I don't know how ...
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27 views

Computing Follow sets of Grammar for LL(1) parser

I am trying to compute the Follow set of the following Grammar: E -> E' E A A -> + | * E -> num E' -> num I start by adding the end of string symbol, ...
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2answers
317 views

Is this an LL(1) grammar? How to solve First - Follow conflict?

im trying to check if this grammar is LL(1). S -> L = R L -> * L | id R -> L | R + R | num As you can see there is a Left recursion on R production. So i remove that and what i get is: S -> L = ...
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1answer
76 views

What is the time complexity of finding the FIRST and FOLLOW sets?

Given how important these are for parsing, I'm surprised I wasn't able to find anything about their complexity. I'm interested in all combinations of: What is the (edit: best known) time complexity ...
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43 views

Abstract syntax tree: expression->operation->lhs|rhs vs expression->lhs|operation|rhs - what should I take into account in decision?

I am trying to build class hierarchy for the abstract syntax tree of First Order Logic as specified in the grammar https://github.com/antlr/grammars-v4/blob/master/fol/fol.g4 (ANTLR parser generator). ...
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1answer
39 views

Grammars and Parsing: Ambiguity in Sequences

BACKGROUND I am writing a grammar and parser for a domain-specific language. There is a specific form of expression that, while simple, is giving me headaches. Given terminals: "a": KEYWORD "b": ...
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1answer
20 views

Why shift means push terminal symbol and state into the stack? Why not push only state?

Shift means that you need to put the status and terminal symbol on the stack. But what is the terminal symbol used for? After all, if the reduce command is executed, both the state and the terminal ...
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1answer
75 views

Build LL(1) parsing table for grammar S -> iSeS | iS | a

Task Bulid parsing table for grammar S -> iSeS | iS | a Resolve conflicts in this table and simulate parser work for word ...
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1answer
596 views

Convert ambiguous grammar to unambiguous and SLR(1)

I have the following ambiguous operator grammar: E->E+E*E | E-E*E E->E+E | E-E | E+E | E*E | E/E E->(E) | x I must convert it to an unambiguous one ...
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1answer
209 views

LR(1) parsing, problem with look ahead symbols

I understand the concept of LR(1) parsing and lookahead symbols. I have the solution to the exercise and it does not agree with my solution. I'm trying to fill the LR(1) parsing table for the grammar ...
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326 views

Syntax Directed Translation Scheme for Postfix to Infix Notation

I'm reading Compilers Principles, Techniques and Tools textbook and I encountered a problem from exercise 2.3 We have to construct a syntax-directed translation scheme that translates arithmetic ...
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62 views

Converting from cfg to cnf (Chomsky normal form)

I am trying to convert this grammar from context free grammar with kleene star productions into the Chomsky normal form equivalent. I am having a hard time trying to understand how to do this, I need ...
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1answer
433 views

How to determine valid handle for given bottom up parser?

I came across following question: Consider the grammar: $E → E + n\text{ | }E × n\text{ | }n$ For a sentence n + n × n, the handles in the right-sentential form of the reduction are (...
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26 views

Is $LR(k) \subset SLR(k+1)$ for $k=1,2,…$? [duplicate]

I know that: Point 1: Set of languages accepted by $LR(0)$ parsers $\subset$ Set of languages accepted by $SLR(1)$ parsers Does this logic hold for higher $k$'s? That is, does following fact hold?...
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1answer
67 views

CYK result de-transformation

Suppose we have a rules derived from a treebank. And in order to get a syntax tree of a given sentence we use the cyk algorithm. In order to use the cyk we should convert the rules into chomsky normal ...
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56 views

Creating a grammar for a a language for instructions, with repititions

I have a language that consists of instructions for movement on a 2D-plane. You start at coordinate [0,0] The instructions DOWN 1 UP 10 LEFT 5 RIGHT 1 means you ...
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42 views

Understanding the rules of parsing table construction

I'm studying top-down parsing, especially LL(1) parsing. However, I cannot understand what is the meaning of rules. Example grammer is like this S → ( S ) S | $\epsilon$ How can I derive like ...
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205 views

The rightmost derivation is possible with the same rule of leftmost derivation

Can someone please help me in understanding the statement. What does it exactly mean? What I think it means is that: the derivation produces by the leftmost derivation is also possible with rightmost ...
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50 views

Get grammar from his LALR(1) parsing table

I have a problem with this exercise. This is the LALR(1) parsing table for the grammar G. How can i get the productions of G? Thanks :)
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1answer
476 views

Handling epsilon productions in recursive descent parsing

I am working on a recursive descent parser for lambda calculus. In my grammar, after removing left-recursion, I am left with the following two productions: ...
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1answer
160 views

Is this a correct grammar for untyped lambda calculus?

I am trying to write a recursive-descent parser for untyped lambda calculus. While researching the way of formulating the grammar, I managed to put together something like this: ...
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1answer
41 views

What is Follow(X) when there's a rule, A -> XBCD where First(B) and First(C) contain empty, but First(D) do not

I have a question about follow sets. Suppose there's a rule, A -> XBCD B -> $\beta$ | $\epsilon$ C -> $\gamma$ | $\epsilon$ D -> $\delta$ What is Follow(X)? Is it (First(B) - $\...
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30 views

Name for a property of grammars

Parsing s-expressions is almost trivial. This is true for both automated processes (and thus implies ease of implementation of such processes) and for a human readers of printed s-expressions. It is ...
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1answer
431 views

Not getting the clear picture of Goto actions , reduce and shift actions in SLR Parsing

I am going through the following lecture notes on LR parsing : https://www3.nd.edu/~dthain/courses/cse40243/fall2016/chapter4b.pdf For the following grammar : The following LR automation has been ...
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1answer
544 views

LL1 parsing algorithm for strings generated by a given grammar

How to describe a $\operatorname{LL(1)}$ parsing algorithm for strings generated by a given grammar? I have to design a parser for a specific grammar. Let $G$ be the grammar described as: $$S \...
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826 views

Proof of every regular language has a LL(1) grammar

I tried some examples and found that LL(1) grammar always exist. I tried searching for formal proof but didn't find any. Can someone give a formal proof for the above statement?
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435 views

Convert Source Code into English Text?

Is there a way to convert, i.e., C code into English? The purpose would be to convert source code into a Text-To-Speech converter which would enable someone to "listen" to source code. EDIT: An ...
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63 views

Is Kalman filter used in automata (besides cellular automata) and parsing grammars?

I am new to Kalman filter and parsers. I understand that it's suitable for prediction/estimation on the go, when you have something to measure (not only the model), and when changes always occur in ...
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1k views

Difference between LR parsing and Shift-Reduce parsing?

I'm learning natural language processing and I can't understand the difference between Shift-Reduce parser and LR parser. As I've understood from Wikipedia, shift-reduce is just a name of a class of ...
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234 views

Is this depth-first top-down parsing algorithm a recursive descent top-down parsing algorithm?

In Thomas Sudkamp's book, Machine and Languages, there is a depth-first top-down parsing algorithm (please see the algorithm here). My main question is: 1) Is this algorithm a (backtracking) ...
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1answer
9k views

LL(1) parsing table construction

i have the following CFG E -> ABC A-> a|Cb|epsilon B-> c|xA|epsilon C-> y|z and the First of the Non-Terminal : ...
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125 views

Is grammar S→aaab | aab in LL(2) but not SLL(2)?

I'm trying to figure out how to create grammars which are LL(k) and not SLL(i). Is this grammar LL(2) and not SLL(2)? $S \to aaab \mid aab$ Where S is a starting symbol. I think it is not SLL: ...
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1answer
85 views

Is there any precedence for symbols for constructing parse trees? [duplicate]

I am wondering if some symbols such as the ones in propositional logic have precedence over others in drawing parse trees. For example, the sentence: p ∧ q → r, ...
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1answer
36 views

Unsure about parse tree of PCFG

I'm new to build parse trees and I'm really unsure if I'm doing this right. So I have this example Grammar (S->Sa, S->aSa, S->a) and the word I'm parsing is simply aaaa. My solution would look like ...
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328 views

how to determine the action from the stack using the LR parsing tables?

I've been having a hard time wrapping my mind around the LR parsing table. Say I have the following table given the input action of id+id*id$ how does Stack ...
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75 views

Linear time parsing from star of context free language

I was wondering if there are cases in which the star closure of a language can make the resulting language easier to parse. In particular, if I have this grammar: ...
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2answers
239 views

generating recursive descent parser

I have a grammar, $L \to A \langle A \rangle^*$ $A \to () \mid (L)$ but I am not sure how to generate parser for $\langle A \rangle$. I know in other case, for example, if $E \to T \langle^*T\...
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61 views

Can we say we reduced a rule if we reduced an equivalent set of smaller rules?

I have constructed an SLR(1) parsing table with the following rules. S -> S + S + S (rule 1) S -> S + S (rule 2) S -> y Is reducing rule 2, then shifting + and y, then again rule 2, equivalent to ...
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455 views

LR(1) constructing DFA

Consider the following grammar, where $ [ \ ] \ | \ , \ $ are terminal symbols $ \begin{eqnarray} L \rightarrow [ \ ] \qquad(1) \\ L \rightarrow [ \ H\ T\ ] \qquad(2) \\ H \rightarrow L \qquad (3) ...
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1answer
126 views

What is a preterm parser?

I am working with HOL-Light parser and keeping seeing references to preterm parser. What is a preterm parser? The most informative statement I find is from the HOL-Light reference for the ...
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2answers
107 views

Which Type of Grammar is this?

I am learning Compiler Design. Can somebody explain what type of Grammar this is? The answer given is $LL(1)$ but there exists a left recursion in the grammar so it cannot be $LL(1)$. I derived the ...
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1answer
624 views

Construct SLR Parse table problems

Consider the augmented grammar G is: S` -> S S -> a S -> (T) T -> T,S T -> S I have tried to construct parse table. But, when I read '(' ...
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1answer
30 views

Grammar Recursive Descent

I have this Grammar below: ...
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1answer
772 views

What is the time complexity of LR parsers?

Bottom up parsers in worst case take O($n^3$) time, and i believe that LR parser being a bottom up parser should also take O($n^3$) time, but i read on wiki that they are able to solve problems in ...
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1answer
30 views

Compilers: how to find first and follow sets?

I sort of know how to solve the problem but I am not sure how to do it in a systematic way. Could someone provide a step-by-step solution especially for the follow set one? Thanks!
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1answer
24 views

Parsing table confusion [closed]

I've been researching the different answers I've been given to this, would somebody just be able to give me a clear answer of the difference between Shift, reduce and go-to. - In a parsing table. Of ...
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1answer
506 views

How should I show that a grammar is not LL(1) and convert grammar to LL(1)

I'm trying to find the ambiguity in this grammar so I can remove it and convert it to LL(1), however for the life of me, I can't find the ambiguity. Moreover, I think there is cycle between X and Y ...
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2answers
841 views

I'm having trouble with Parse Trees

I am doing homework and I have the following problem: Consider the grammar: ...
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1answer
239 views

Is this $LL(1)$ grammar valid?

Is the following a valid $LL(1)$ grammar: $ \begin{align} S &\rightarrow L \$ \\ L &\rightarrow M L_2 \\ L_2 &\rightarrow \underline{::} L \\ L_2 &\rightarrow \epsilon \\ M &\...
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1answer
621 views

Left recursion for LL(1) [closed]

Hi I am trying to solve a LL(1) form question for first n follow rule The question is A::=BC|C B::=Bd|ef C::=gh|j What I have done to eliminate left recursion <...

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