Questions tagged [parsers]

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

104 questions with no upvoted or accepted answers
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10
votes
1answer
392 views

Shift-resolve parsing - questions

I've recently came across a paper describing the parsing technique mentioned in the title. Unfortunately, the terminology used in said paper is somewhat beyond my comprehension, so I've been ...
8
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0answers
297 views

Can any PEG grammar be parsed in linear time?

On the Wikipedia for PEG it is claimed: Any PEG can be parsed in linear time by using a packrat parser, as described above. However, packrat parsers can't handle left recursion. You can eliminate ...
6
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0answers
616 views

How does this left-associative recursive descent parser work?

For personal enlightenment, I'm trying to write a recursive descent parser for lambda calculus without abstraction, i.e., just identifiers and function application. The BNF grammar that describes the ...
6
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0answers
71 views

Is THEADS the same as FIRST?

I'm reading the paper "A Practical General Method for Constructing LR(k) Parsers" by David Pager, and it contains the following paragraph: We will first of all briefly review the LR(1) parsing and ...
5
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1answer
127 views

Why is XML hard to parse?

I was chatting with a friend about my love/hate relationship with XML. He made the comment that, "xml is broken primarily because parsers for recursive self-defined document are basically ...
4
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0answers
55 views

Algorithm for undirected projective dependency parsing

I am looking for an algorithm that will get an optimal projective undirected dependency parse. That is, given the sentence 'Mary does love John', and an edge-weight function $f$ (that is, a function ...
4
votes
0answers
111 views

Unambiguous context-free language that can't be parsed in linear time by backtracking recursive descent?

Is there a context-free language that can be expressed with an unambiguous grammar but can't be expressed with a grammar that would result in linear-time backtracking recursive descent parsing? The ...
4
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0answers
162 views

How does Earley parsing using an automaton work?

As described in this paper, you can use an pre-computed automaton to speed up an Earley parse. I'm not interested in the rigorous proof of this, but just how the basic algorithm works so that I can ...
4
votes
1answer
163 views

Are there automatic transformation of grammar algorithms?

From time to time you can write a grammar that creates shift/reduce conflict (for example) but after reading the grammar you notice that if you rewrite the productions the conflict will go away, ...
3
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0answers
27 views

How to model grammar ambiguity

Say you have a (context-free) grammar, and you wish to mathematically model the magnitude of the ambiguity possible under this grammar, across the space of all possible** input strings. Practically, ...
3
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0answers
279 views

How would I build a parser generator for a context free grammar using Pushdown Automata?

I am building a parser generator, not for any project in particular, just for fun to improve my understanding of parsing, grammars, languages, etc. I am at the point where I have lexer generation ...
3
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0answers
789 views

Parsing family of grammars, determine if LR(k)

Consider the family of grammars $G_n,~n\geq2$. $$S \rightarrow A_ib_i~,~for~~1\leq i \leq n$$ $$A_i \rightarrow a_jA_i~|~a_j~,~for~~1 \leq i,j \leq n~~and~~i \neq j$$ where multiple alternative right ...
2
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0answers
22 views

Generating an "approximate" grammar

This is my first time posting here, so I hope I'm on topic. I have a table of natural-language data of the form ...
2
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0answers
20 views

Unparsing an operator grammar in the face of ambiguity

I'm using the grammar scheme of Danielsson and Norell ("Parsing Mixfix Operators"). The short version is: user defined mixfix operators such as _+_ or <...
2
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0answers
539 views

How to generate LL(1) parse table

Given the following grammar: S -> A a A -> B D B -> b B -> ε D -> d D -> ε first would be: ...
2
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0answers
183 views

Does SLR(0), LALR(0) exists?

I read about LL(1), LR(0), SLR(1) and LALR(1) in many online sources and even in dragon book. However I found that no one talks about LL(0), SLR(0) and LALR(0). So I googled and come up against these ...
2
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0answers
34 views

what are the limitations of definite clause grammars?

Definite clause grammars have been around for a long time but there are not the answer to every parsing problem or we would not need to invent new formalisms. Are there any languages they cannot ...
2
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0answers
112 views

What strategies exist for handling/resolving ambiguity in parsers?

I define a parser as a context-free grammar with semantic actions for each production. It is not defined in what order the semantic actions run, just that the semantic actions of the non-terminals in ...
2
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0answers
40 views

How to know a certain grammar is parse-able

Is it possible to parse all kinds of structured data and give them a semantic meaning? For example, C++ is a really complicated language and I could never imagine a parser would be possible for it. ...
2
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0answers
135 views

Expanding an Earley parse forest

I have a small context-free grammar, which I would like to use to turn input strings into parse trees. I need to get all possibilities in case of ambiguity (so shift-reduce is out), and there's quite ...
2
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0answers
87 views

Examples of context-free grammars with worst-case complexity

What are some examples of context-free grammars that necessarily trigger cubic worst-case complexity for GLR parsers? I have seen a mention of the example S $\rightarrow$ SSS | SS | "a" but I would ...
2
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0answers
478 views

SLR vs CLR parser

In SLR we use follow set of a non terminal for determining reduce moves and in CLR we use lookaheads for the same. How does using lookaheads actually help in improving the performance of the parser ? ...
2
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0answers
70 views

Correct bracketing check with rotate operation on position i

Given sequence (length $N$) of brackets like $($ and $)$. The task is to implement data structure which supports following operations: Check whether the sequence is correctly bracketed Rotate bracket ...
2
votes
0answers
343 views

How to find conflicts in LALR parser?

I have a LR analyser and I can't find out how to know whether the grammar is or is not LALR(1). I think that I have to merge states with the same rules. So I have to merge states: $2 - 12, 3 - 13, 4 -...
2
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0answers
768 views

lexical scoping vs. dynamic scoping

I'm wondering about the result of this program as I get confused when it comes to lexical scoping and dynamic scoping. ...
2
votes
1answer
274 views

Negative lookahead in LR parsing algorithm

Consider such a rule in grammar for an LR-family parsing generator (e.g YACC, BISON, etc.): Nonterminal : [ lookahead not in {Terminal1, ..., TerminalN} ] Rule ; ...
1
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0answers
21 views

Condition of LL(3) grammer

To find out whether a grammar G is LL(1) or not, we test this condition among other conditions, "If whenever A -> alpha | beta are two distinct productions ...
1
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1answer
49 views

More efficient way to parse array into binary search tree

Let's assume I have array which I need to parse into binary tree ...
1
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0answers
12 views

How do bottom up parser evaluate things that need an inherited attribute?

I learned that Bottom up parsers use only synthesized attributes to evaluate semantics. Which makes sense considering that it would be very hard to evaluate an inherited attribute in bottom up ...
1
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0answers
34 views

Generating a recursive descent parser for grammar having Kleene star

From what I have been taught, I cannot use left-recursive, nondeterministic, or ambiguous grammars in recursive descent parsers. So, here is the grammar: \begin{align} &E \to E+T \mid T \\ &T \...
1
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0answers
35 views

Understanding the concept of "Viable Prefixes"

I was going through the text: Compilers: Principles, Techniques and Tools by Ullman et. al where I came across the concept of viable prefix and I faced some difficultly in grasping the concept. So I ...
1
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0answers
23 views

Is there a direct way to obtain the RE for the handle-finding DFA of a grammar?

LR parser for a (CFG) grammar uses a handle-find automaton (which is a DFA) to find the handles. Such automata can be constructed by computing the canonical collection of sets of LR(0)/LR(1) items. Is ...
1
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0answers
49 views

How to write "∀x.F(x)" for "F(x)=λx.Φ(x)" in one expression (sequel from question about "∀(λφ. (φ x m→ φ y))"?

This question is sequel from How to understand quantifier without predication " ∀(λφ. (φ x m→ φ y))"? which further explains the notation and context. So - I have anonymous Boolean-valued ...
1
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0answers
30 views

Using DPDA instead of LR parsers

If LR parsers handle only DCFLs than why we don't just use dpda to parse these languages? What are advantages of using LR parsers over DPDA? Is it that it is easy to built autonomously or something ...
1
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0answers
37 views

CYK algorithm - how to handle unknown terminals given in a sentence to parse?

There is a given treebank which we derive the Probabilistic context free grammar. I wonder how do one handles with a given sentence which includes terminals that don't exist in the derived rules? Is ...
1
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0answers
17 views

State of the art of parser handling of offset errors

Say you are parsing a complicated binary file but there is 1 extra byte inserted somewhere. This could completely mess up the entire parse, but if you just looked ahead one token you would see the ...
1
vote
1answer
86 views

SLR(1) Table construction, FIRST and FOLLOWS

when constructing the SLR(1) table for some grammar I need to compute the FOLLOW set for all terminals in order to decide where and when to reduce. Do I compute theme for the augmented grammar or ...
1
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0answers
31 views

Is there any difference in the expressiveness of boolean grammars versus definite clause grammars?

Definite clause grammars have been around a long time and are included in logic languages such as Prolog. They can be translated into (are just syntactic sugar for) Prolog programs and are therefore ...
1
vote
0answers
167 views

Do SLR(1) parsers have lookahead?

The SLR(1) parses AFAIK does not have any lookahead with it then why do we write it as SLR(1) and not as SLR(0). The thing about parsers which I read online taught me that if it's LR(K) then K ...
1
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0answers
25 views

Clear definitions of various terms related to top down parsers and classification of the same

I am trying to clearly define various terms related to top down parser "so that I can relate them and come up with clear classification". Now this efforts might seem unnecessary as the terms I am ...
1
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0answers
554 views

How to design a LL(1) grammar for basic regular expression?

I try to design a LL(1) grammar to parse the basic regular expression. Here's the origin grammar.(\| is the escape character, since | is a special character in grammar's pattern). ...
1
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0answers
726 views

Are LL(1) grammars a subset of LR(0) grammars?

As far as I've understood it seems that LL1 are a subset of LR0, but studying the following grammar I end up in a contraddiction. Grammar : S -> (S) | [S] | {S} | ε This is an LL1 while it seems ...
1
vote
0answers
492 views

Can a YACC parse an ambiguous grammar

I found a question while studying compilers :- Given a grammar E->E+E/E×E/number The above grammar is fed to a YACC with semantic rules for parsing. What will be the action of the YACC. 1) it ...
1
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0answers
83 views

Generate an AST from an indefinite grammar and logic

As said in the title, I have to generate an AST from a grammar and logic (or a"syntax" if you prefer). This grammar and syntax are both indefinite in the program, meaning that it is the user (a ...
1
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0answers
443 views

How do we evaluate semantic actions in L attributed SDT?

I came across following problem: $S→ER$ $R→∗E\{print(′∗′);\}R∣ε$ $E→F+E\{print(′+′);\}∣F$ $F→(S)∣id\{print(id.value);\}$ Here $id$ is a token that represents an integer and $id.value$ ...
1
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0answers
535 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 ...
1
vote
0answers
163 views

Can the HTML5 parsing algorithm be implemented in linear time?

Can the HTML5 parsing algorithm (https://html.spec.whatwg.org/multipage/parsing.html#parsing) be implemented in $O(n)$, or at worst $O(n\mathop{log}n)$, time, even for malicious input? It seems ...
1
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0answers
86 views

Where is left recursion in this little CF grammar?

S → D D → E | EC E → anyId C → B | .D | B.D B → <S> | <SA> A → ,S | ,SA The tool I am using keeps complaining about left recursion in this grammar. I ...
1
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0answers
229 views

Is the Java 8 Grammar still a LALR(1) grammar?

As I found out here: http://www.eclipse.org/jdt/core/howto/generate%20parser/generateParser.html , the Java Version of 2005 (might be Java 6, I'm not sure) is a LALR(1) grammar. However, I couldn't ...
1
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0answers
41 views

Determining the set of valid next terminals when generating from a CFG

I am trying to generate random sentences from a context-free grammar. During each step, the next non-terminal to be generated is determined according to some probabilistic criteria irrelevant to this ...