PEG, an Implementation Of A Packrat Parsing Expression Grammar in Go

PEG, an Implementation of a Packrat Parsing Expression Grammar in Go  

A Parsing Expression Grammar ( hence peg) is a way to create grammars similar in principle to regular expressions but which allow better code integration. Specifically, peg is an implementation of the Packrat parser generator originally implemented as peg/leg by Ian Piumarta in C. A Packrat parser is a "descent recursive parser" capable of backtracking and negative look-ahead assertions which are problematic for regular expression engines.

Installing

go get -u github.com/pointlander/peg

Building

Using Pre-Generated Files

go install

Generating Files Yourself

You should only need to do this if you are contributing to the library, or if something gets messed up.

go run build.go or go generate

With tests:

go run build.go test

Usage

peg [<option>]... <file>

Usage of peg:
  -inline
      parse rule inlining
  -noast
      disable AST
  -output string
      specify name of output file
  -print
      directly dump the syntax tree
  -strict
      treat compiler warnings as errors
  -switch
      replace if-else if-else like blocks with switch blocks
  -syntax
      print out the syntax tree
  -version
      print the version and exit
      

Sample Makefile

This sample Makefile will convert any file ending with .peg into a .go file with the same name. Adjust as needed.

.SUFFIXES: .peg .go

.peg.go:
    peg -noast -switch -inline -strict -output $@ $<

all: grammar.go

Use caution when picking your names to avoid overwriting existing .go files. Since only one PEG grammar is allowed per Go package (currently) the use of the name grammar.peg is suggested as a convention:

grammar.peg
grammar.go

PEG File Syntax

First declare the package name and any import(s) required:

package <package name>

import <import name>

Then declare the parser:

type <parser name> Peg {
    <parser state variables>
}

Next declare the rules. Note that the main rules are described below but are based on the peg/leg rules which provide additional documentation.

The first rule is the entry point into the parser:

<rule name> <- <rule body>

The first rule should probably end with !. to indicate no more input follows.

first <- . !.

This is often set to END to make PEG rules more readable:

END <- !.

. means any character matches. For zero or more character matches, use:

repetition <- .*

For one or more character matches, use:

oneOrMore <- .+

For an optional character match, use:

optional <- .?

If specific characters are to be matched, use single quotes:

specific <- 'a'* 'bc'+ 'de'?

This will match the string "aaabcbcde".

For choosing between different inputs, use alternates:

prioritized <- 'a' 'a'* / 'bc'+ / 'de'?

This will match "aaaa" or "bcbc" or "de" or "". The matches are attempted in order.

If the characters are case insensitive, use double quotes:

insensitive <- "abc"

This will match "abc" or "Abc" or "ABc" and so on.

For matching a set of characters, use a character class:

class <- [a-z]

This will match "a" or "b" or all the way to "z".

For an inverse character class, start with a caret:

inverse <- [^a-z]

This will match anything but "a" or "b" or all the way to "z".

If the character class is case insensitive, use double brackets:

insensitive <- [[A-Z]]

(Note that this is not available in regular expression syntax.)

Use parentheses for grouping:

grouping <- (rule1 / rule2) rule3

For looking ahead a match (predicate), use:

lookAhead <- &rule1 rule2

For inverse look ahead, use:

inverse <- !rule1 rule2

Use curly braces for Go code:

gocode <- { fmt.Println("hello world") }

For string captures, use less than and greater than:

capture <- <'capture'> { fmt.Println(text) }

Will print out "capture". The captured string is stored in buffer[begin:end].

Testing Complex Grammars

Testing a grammar usually requires more than the average unit testing with multiple inputs and outputs. Grammars are also usually not for just one language implementation. Consider maintaining a list of inputs with expected outputs in a structured file format such as JSON or YAML and parsing it for testing or using one of the available options for Go such as Rob Muhlestein's tinout package.

Files

• bootstrap/main.go - bootstrap syntax tree of peg
• tree/peg.go - syntax tree and code generator
• peg.peg - peg in its own language

Projects That Use peg

Here are some projects that use peg to provide further examples of PEG grammars:

• https://github.com/tj/go-naturaldate - natural date/time parsing
• https://github.com/robmuh/dtime - easy date/time formats with duration spans
• https://github.com/gnames/gnparser - scientific names parsing

See Also

• http://en.wikipedia.org/wiki/Parsing_expression_grammar
• http://pdos.csail.mit.edu/~baford/packrat/
• http://piumarta.com/software/peg/

Author: Pointlander
Source Code: https://github.com/pointlander/peg 
License: BSD-3-Clause license

#go #golang 

What is GEEK

Buddha Community

What's new in the go 1.15

Go announced Go 1.15 version on 11 Aug 2020. Highlighted updates and features include Substantial improvements to the Go linker, Improved allocation for small objects at high core counts, X.509 CommonName deprecation, GOPROXY supports skipping proxies that return errors, New embedded tzdata package, Several Core Library improvements and more.

As Go promise for maintaining backward compatibility. After upgrading to the latest Go 1.15 version, almost all existing Golang applications or programs continue to compile and run as older Golang version.

#go #golang #go 1.15 #go features #go improvement #go package #go new features

PEG, an Implementation Of A Packrat Parsing Expression Grammar in Go

PEG, an Implementation of a Packrat Parsing Expression Grammar in Go  

A Parsing Expression Grammar ( hence peg) is a way to create grammars similar in principle to regular expressions but which allow better code integration. Specifically, peg is an implementation of the Packrat parser generator originally implemented as peg/leg by Ian Piumarta in C. A Packrat parser is a "descent recursive parser" capable of backtracking and negative look-ahead assertions which are problematic for regular expression engines.

Installing

go get -u github.com/pointlander/peg

Building

Using Pre-Generated Files

go install

Generating Files Yourself

You should only need to do this if you are contributing to the library, or if something gets messed up.

go run build.go or go generate

With tests:

go run build.go test

Usage

peg [<option>]... <file>

Usage of peg:
  -inline
      parse rule inlining
  -noast
      disable AST
  -output string
      specify name of output file
  -print
      directly dump the syntax tree
  -strict
      treat compiler warnings as errors
  -switch
      replace if-else if-else like blocks with switch blocks
  -syntax
      print out the syntax tree
  -version
      print the version and exit
      

Sample Makefile

This sample Makefile will convert any file ending with .peg into a .go file with the same name. Adjust as needed.

.SUFFIXES: .peg .go

.peg.go:
    peg -noast -switch -inline -strict -output $@ $<

all: grammar.go

Use caution when picking your names to avoid overwriting existing .go files. Since only one PEG grammar is allowed per Go package (currently) the use of the name grammar.peg is suggested as a convention:

grammar.peg
grammar.go

PEG File Syntax

First declare the package name and any import(s) required:

package <package name>

import <import name>

Then declare the parser:

type <parser name> Peg {
    <parser state variables>
}

Next declare the rules. Note that the main rules are described below but are based on the peg/leg rules which provide additional documentation.

The first rule is the entry point into the parser:

<rule name> <- <rule body>

The first rule should probably end with !. to indicate no more input follows.

first <- . !.

This is often set to END to make PEG rules more readable:

END <- !.

. means any character matches. For zero or more character matches, use:

repetition <- .*

For one or more character matches, use:

oneOrMore <- .+

For an optional character match, use:

optional <- .?

If specific characters are to be matched, use single quotes:

specific <- 'a'* 'bc'+ 'de'?

This will match the string "aaabcbcde".

For choosing between different inputs, use alternates:

prioritized <- 'a' 'a'* / 'bc'+ / 'de'?

This will match "aaaa" or "bcbc" or "de" or "". The matches are attempted in order.

If the characters are case insensitive, use double quotes:

insensitive <- "abc"

This will match "abc" or "Abc" or "ABc" and so on.

For matching a set of characters, use a character class:

class <- [a-z]

This will match "a" or "b" or all the way to "z".

For an inverse character class, start with a caret:

inverse <- [^a-z]

This will match anything but "a" or "b" or all the way to "z".

If the character class is case insensitive, use double brackets:

insensitive <- [[A-Z]]

(Note that this is not available in regular expression syntax.)

Use parentheses for grouping:

grouping <- (rule1 / rule2) rule3

For looking ahead a match (predicate), use:

lookAhead <- &rule1 rule2

For inverse look ahead, use:

inverse <- !rule1 rule2

Use curly braces for Go code:

gocode <- { fmt.Println("hello world") }

For string captures, use less than and greater than:

capture <- <'capture'> { fmt.Println(text) }

Will print out "capture". The captured string is stored in buffer[begin:end].

Testing Complex Grammars

Testing a grammar usually requires more than the average unit testing with multiple inputs and outputs. Grammars are also usually not for just one language implementation. Consider maintaining a list of inputs with expected outputs in a structured file format such as JSON or YAML and parsing it for testing or using one of the available options for Go such as Rob Muhlestein's tinout package.

Files

• bootstrap/main.go - bootstrap syntax tree of peg
• tree/peg.go - syntax tree and code generator
• peg.peg - peg in its own language

Projects That Use peg

Here are some projects that use peg to provide further examples of PEG grammars:

• https://github.com/tj/go-naturaldate - natural date/time parsing
• https://github.com/robmuh/dtime - easy date/time formats with duration spans
• https://github.com/gnames/gnparser - scientific names parsing

See Also

• http://en.wikipedia.org/wiki/Parsing_expression_grammar
• http://pdos.csail.mit.edu/~baford/packrat/
• http://piumarta.com/software/peg/

Author: Pointlander
Source Code: https://github.com/pointlander/peg 
License: BSD-3-Clause license

#go #golang 

How to Upload and Store Images in MySQL using Node.js and Express

Today we are going to explore the basic usage of Express-FileUpload. In addition to this, I will show you how you can save/update a user record with a profile image that you can upload.

Chapters:
0:00 Introduction:
1:16 NPM Project Setup
3:54 Creating Express Server
5:51 Setting up Layouts & Routes
9:46 Express Upload Form
21:50 User Card
33:40 Database
52:05 Ending

Source Files:
https://raddy.co.uk/blog/upload-and-store-images-in-mysql-using-node-js-express-express-fileupload-express-handlebars/

#node.js #express #express-fileupload #express-handlebars #mysql #upload and store images

JSON Parsing in Android - Step by Step Implementation

JSON Structures in Android

JSON uses two types of brackets that are as follows:

• [] – To declare the elements of Array in JSON, they’re written in square brackets.
• {} – To create JSON objects, the elements are written in curly brackets.

JSON has the following types of structures that are:

1. JSON Objects

The elements inside the curly brackets are known as Objects.

2. JSON Array

A list of values, known as Arrays.

3. JSON Key-Value

This data is stored as a pair of keys and values. Here the keys can be a name, a number for which the values can be Seema, 98767586 etc.

Why JSON Parsing in Android over XML?

Let us see some reasons for why to choose JSON over XML:

• It is much easier and quicker with high performance
• It can use arrays
• Its libraries do not depend on other libraries
• The codes written in JSON are short, clean and easy to understand
• It is free to open use and open-source tool
• In JSON value retrieval is easy
• It has a fully automated way of serializing/deserializing JavaScript.
• It is supported by many Ajax toolkits and most of the backend technologies.

Examples of XML and JSON

Let us see the code difference of JSON and XML files:

XML Example:

<?xml version= “1.0” encoding= “” ?>
<student>
        <student>
  <name> Sia Sharma</name>
  <city> Chandigarh</city>
         </student>
        <student>
  <name>Dimple D’souza</name>
  <city> Nagpur</city>
         </student>
      <student>
  <name>Anna Jones</name>
  <city> Mumbai</city>
         </student>
  </student>

JSON Example:

{ “students”: [
{ “name”: “Sia Sharma”, “city”: “Chandigarh”},
{ “name”: “Prachi D’Souza”, “city”: “Nagpur”},
{ “name”: “Annas Jones”, “city”: “Mumbai”}
]}

I hope the difference is all clear in front of you. This is how simple JSON is and how easily it could be understood.

#android tutorials #json parsing in android #json parsing in android example #json parsing in android step by step #json parsing with android #read json file android

Building an Express-style API in Go with Fiber

Introduction

If you are familiar with Express, you may recognize that Fiber is inspired by the awesome Node.js framework — except it is written in Go. Why?

Well, because Go is very fast, low on memory footprint, and highly performant for building scalable web servers and applications.

Fiber leverages these performance benefits and features. Firstly, it is based on the fasthttp package, which is the fastest HTTP client library in the Go ecosystem. From benchmark results, fasthttp is 10 times as fast as the net/http native Go client package.

In this post, we are going to explore Fiber by looking at its features and components, such as routing, middleware support, and context. At the end of the day, we should then be able to apply these features and build a demo application that interacts with a database of our choice.

Prerequisites

To easily follow along with this tutorial, we should have at least a basic knowledge of the Go programming language. It might also be beneficial to know a little bit of Express, as this could help in quickly understanding Fiber from an architecture point of view.

Also, make sure you have the Postgres.app for your OS of choice — you can download it here. Also, you can install any GUI client for Postgres. In this article, we will be using Postico, which you can download here.

Finally, make sure you have the latest version of Go installed on your machine. Instructions to do so can be found in the documentation.

In the coming section, we will talk briefly about the motivation behind Fiber. Let’s go.

#go #fiber #express #api #developer