apg-lite

APG Lite

apg-lite is a light-weight parser of ABNF grammars. It is a parser only. It relies on apg-js, version 4.3.0 or higher, with the new --lite option to generate ESM grammar objects. apg-lite features:

• Parses only JavaScript strings, whereas apg-js can parse any arbitrary array of positive integers.
• Retains only three of the eight SABNF superset operators of apg-js.
  • UDT, (User-Defined Terminals) Handwritten, phrase-matching code snippets.
  • AND, The positive look-ahead operator (see syntactic predicates).
  • NOT, The negative look-ahead operator.
• The AST has been simplified (see ./ast-app/).
• Tracing (debugging) the parse tree has been simplified (see ./trace-app/).
• Statistics collection (profiling) has been simplified (see ./trace-app/).
• apg-lite is fully contained in a single JavaScript file.
  • ./lib/parser.js contains ECMAScript Modules (ESM) which can be import-ed into your application.
  • ./lib/web-parser.js can be scripted into your web page application with no bundling necessary.

A number of example application are included here to demonstrate the use of apg-lite in both Node.js and web page applications. Each example application is in its own directory. The documentation for each is in the file documentation.md. Most (but not all) examples will be presented as both Node.js and web page applications.

• ./basic-app/ - A simple parser demonstrating the most basic construction and use of a parser.
• ./ast-app/ - Use of the AST - how to construct the AST and translate or semantically manipulate the phrases captured by the AST nodes. Demonstrates generating an XML version of the AST.
• ./udt-app/ - Use of a UDT, a handwritten code snippet to recognize a somewhat complicated phrase.
• ./lookahead-app/ - Demonstration of the look ahead operators.
• ./trace-app/ - How to debug and profile the parse tree.
  • Tracing is the primary means of debugging a grammar or input string.
  • Counting node hits serves as a type of profiling, exposing which rules are most often hit.
• ./cool-app/ - A simple demonstration of parsing a string with UTF+32 (in this case emoticon) characters.
• ./uri-app/ - This example builds a light-weight, but robust and well-tested URI parser.

The Node.js applications can all be run from the package.json scripts. Use npm run to see the script names of the demonstrations.

The URI Parser

Note: version 1.0.5 fixes a bug in the URI grammar. The previous versions incorrectly allowed empty strings for the IPv4 octets. No changes to the apg-lite parser or any of the other examples have been made.

The UriParser object in the ./uri-app/ application is of special interest. It is a fully-contained (no dependencies) URI parser. Any URI can be parsed with, for example:

npm run uri -- http://[e-mail]

If no argument is given, the example will parse a pre-chosen representive URI.

UriParser is well-tested with Jest unit tests in the __tests__ directory.

npm test

will run all of the unit tests.

See ./uri-app/documentation.md for complete documentation. See ./uri-app/node-app.js for a sample Node.js application and ./uri-app/web.html for sample web page application.