Ebnf cheat sheet

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Ebnf cheat sheet

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ebnf cheat sheet

Lark can parse all context-free languages. That means it is capable of parsing almost any programming language out there, and to some degree most natural languages too. Beginners : Lark is very friendly for experimentation. It can parse any grammar you throw at it, no matter how complicated or ambiguous, and do so efficiently.

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It also constructs an annotated parse-tree for you, using only the grammar, and it gives you convienient and flexible tools to process that parse-tree. It also provides a variety of sophisticated features and utilities.

Notice punctuation doesn't appear in the resulting tree. It's automatically filtered away by Lark. See the full list of features here.

Check out the JSON tutorial for more details on how the comparison was made. If anyone can point me to one that actually works, I would be happy to add it! Note 2: The parsimonious code has been optimized for this specific test, unlike the other benchmarks Lark included.

Its "real-world" performance may not be as good. Lark comes with a tool to convert grammars from Nearleya popular Earley library for Javascript. It uses Js2Py to convert and run the Javascript postprocessing code segments. Lark is currently accepting pull-requests. See How to develop Lark. If you like Lark and feel like donating, you can do so at my patreon page. If you wish for a specific feature to get a higher priority, you can request it in a follow-up email, and I'll consider it favorably.

Skip to content. Dismiss Join GitHub today GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

Influx Query Language (InfluxQL) reference

The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Learn more. Asked 8 years, 5 months ago. Active 8 years, 2 months ago. Viewed 5k times. Why don't you try yourself? If you're having trouble, come back with a more specific question, because this now reads as "could someone do this for me".

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Good luck! The 'BNF' in this question is under-defined though its meaning can be guessed. Active Oldest Votes. Patrick Lafferty 3 3 silver badges 12 12 bronze badges.

Extended Backus-Naur Form

Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. The Overflow How many jobs can be done at home? Featured on Meta. Community and Moderator guidelines for escalating issues via new response….

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Dark Mode Beta - help us root out low-contrast and un-converted bits. Linked 6. Related Hot Network Questions.In computer scienceBackus—Naur form or Backus normal form BNF is a notation technique for context-free grammarsoften used to describe the syntax of languages used in computing, such as computer programming languagesdocument formatsinstruction sets and communication protocols.

They are applied wherever exact descriptions of languages are needed: for instance, in official language specifications, in manuals, and in textbooks on programming language theory. In Western society, grammar was long regarded as a subject for teaching, rather than scientific study; descriptions were informal and targeted at practical usage. In the first half of the 20th century, linguists such as Leonard Bloomfield and Zellig Harris started attempts to formalize the description of language, including phrase structure.

Meanwhile, string rewriting rules as Formal logical systems were introduced and studied by mathematicians such as Axel Thue inEmil Post s—40s and Alan Turing Noam Chomskyteaching linguistics to students of information theory at MITcombined linguistics and mathematics by taking what is essentially Thue's formalism as the basis for the description of the syntax of natural language.

He also introduced a clear distinction between generative rules those of context-free grammars and transformation rules BNF is a notation for Chomsky's context-free grammars.

Apparently, Backus was familiar with Chomsky's work. As proposed by Backus, the formula defined "classes" whose names are enclosed in angle brackets. Each of these names denotes a class of basic symbols. In the committee's report, Peter Naur called Backus's notation Backus normal form. Donald Knuth argued that BNF should rather be read as Backus—Naur formas it is "not a normal form in the conventional sense", [9] unlike, for instance, Chomsky normal form.

Any mark in a formula, which is not a variable or a connective, denotes itself. Juxtaposition of marks or variables in a formula signifies juxtaposition of the sequence denoted.

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Metalinguistic variables do not require a rule defining their formation. For the purpose of including text among the symbols of a program the following "comment" conventions hold:. By equivalence is here meant that any of the three structures shown in the left column may be replaced, in any occurrence outside of strings, by the symbol shown in the same line in the right column without any effect on the action of the program.

Naur changed two of Backus's symbols to commonly available characters. The " " symbol was originally the word " or " with a bar over it. BNF is very similar to canonical-form boolean algebra equations that are, and were at the time, used in logic-circuit design.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I have a homework problem which I could use some help on.

It doesn't feel right, mainly because it's a WAG. The example in my book Concepts of Programming Languages, Sebesta is not helping me at all. So if anyone has any insight, it would be greatly appreciated. The first grammar seems buggy, or at least needlessly messy. Ultimately you ask yourself what is required. Write it down. Now consider the optional components and use various combinations of them with the required components in the right order of course.

Then reduce what you can be careful not to make a mistake. Learn more. Asked 10 years, 2 months ago. Active 1 year, 5 months ago. Viewed 10k times. Brian McKenna Active Oldest Votes.

ebnf cheat sheet

Abel Andre Artus Andre Artus 1, 12 12 silver badges 20 20 bronze badges. It is much easier to understand and write! Andrew Naguib 2, 1 1 gold badge 16 16 silver badges 32 32 bronze badges. The Overflow Blog. The Overflow How many jobs can be done at home? Featured on Meta. Community and Moderator guidelines for escalating issues via new response…. Feedback on Q2 Community Roadmap. Technical site integration observational experiment live on Stack Overflow.

Triage needs to be fixed urgently, and users need to be notified upon…. Dark Mode Beta - help us root out low-contrast and un-converted bits. Linked EBNF is the same notation used in the Go programming language specification, which can be found here. Not so coincidentally, InfluxDB is written in Go. Identifiers are tokens which refer to database names, retention policy names, user names, measurement names, tag keysand field keys.

ebnf cheat sheet

If you use an InfluxQL keywords as an identifier you will need to double quote that identifier in every query. The keyword time is a special case. In those cases, time does not require double quotes in queries.

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See Frequently Asked Questions for more information. InfluxQL supports decimal integer literals. Hexadecimal and octal literals are not currently supported. String literals must be surrounded by single quotes. Strings may contain ' characters as long as they are escaped i. Duration literals specify a length of time. An integer literal followed immediately with no spaces by a duration unit listed below is interpreted as a duration literal.

Durations can be specified with mixed units. The date and time literal format is not specified in EBNF like the rest of this document. The reference date time is:.

Currently, InfluxQL does not support using regular expressions to match non-string field values in the WHERE clause, databasesand retention polices. Note: To ensure data is successfully replicated across a cluster, the number of data nodes in a cluster must be evenly divisible by the replication factor.

Subscriptions tell InfluxDB to send all the data it receives to Kapacitor. Since InfluxQL does not support joins, the cost of a InfluxQL query is typically a function of the total series accessed, the number of iterator accesses to a TSM file, and the number of TSM blocks that need to be scanned.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.

If nothing happens, download GitHub Desktop and try again. If nothing happens, download Xcode and try again. If nothing happens, download the GitHub extension for Visual Studio and try again. EBNF parser and generic parser generator. As LL 1 grammars operate using alt and seq primitives, allowing for a match on alternative productions or a sequence of productions, generating a parser requires turning the EBNF rules into BNF:.

Of note in this implementation is that the tokenizer and parser are streaming, so that they can process inputs of arbitrary size. Intermediate representations of the grammar may be serialized to Lisp-like S-Expressions. The parser is initialized to callbacks invoked on entry and exit to each terminal and production. A trivial parser loop can be described as follows:. The Branch table is a hash mapping production rules to a hash relating terminals appearing in input to sequence of productions to follow when the corresponding input terminal is found.

This allows either the seq primitive, where all terminals map to the same sequence of productions, or the alt primitive, where each terminal may map to a different production.

The declaration rule is terminals' pass using the alt primitive determining the production to run based on the terminal appearing on the input stream.

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Eventually, a terminal production is found and the token is consumed. For example:. This allows the parser, in some cases, to reproduce starplusand opt rule matches. As BNF does not support a star operator, this is decomposed into a set of rules using alt and seq primitives:.

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Much of this work, particularly the generic parser, is inspired by work originally done by Tim Berners-Lee's Python predictive parser. Full documentation available on Rubydoc. This repository uses Git Flow to mange development and release activity.

All submissions must be on a feature branch based on the develop branch to ease staging and integration. This is free and unencumbered public domain software. These files are covered via the W3C Document License. Skip to content. Dismiss Join GitHub today GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.

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ebnf cheat sheet

EBNF parser and generic parser generator for Ruby. Ruby HTML. Ruby Branch: develop. Find file. Sign in Sign up. Go back.

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Latest commit. Latest commit f64da71 Dec 17, BNF is the original, most simple, mostly used in academic papers of theoretical context, for communicating to humans. There's no one exact specification of BNF.

There's not one single EBNF, but each author or program define their own variant that's slightly different. It is harder to read, but is most used in parsers. They are just syntactical differences. In BNF, the symbol for alternatives is a vertical line.

To translate it to BNF, you'll need to introduce several more rules and nonterminals. In general, BNF notation is good for teaching, explanation, theoretical discussion. It is simple. For example, name-part is not defined. Here's a example describing a simplified Pascal syntax:. Terminals are enclosed by a double quote pair ".

All others are non-terminal. The same constructs can still be used in EBNF. This prevents these characters from being used in the languages, and requires a special symbol for the empty string. BNF syntax can only represent a rule in one line, whereas in EBNF a terminating character, the semicolon, marks the end of a rule.

Furthermore, EBNF includes mechanisms for enhancements, defining the number of repetitions, excluding alternatives, comments, etc. There are lots ambiguities and not well defined. By Xah Lee. Date: Last updated:


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