readme.md

Parse Pact: a compact parser generator

Provides Autonomous Regex Scanners & Entire Parsers At Compile Time

Single header C++-20 library to generate lexer and parser, at compile time or runtime!

Key features

• Single header: immediate to streamline in your project:

#include <parsePact.hpp>

const auto parser=pp::generateParser(" ... grammar...");
parser.parse("...text to be parsed");

• Can generate the parser at compile time:

constexpr auto parser=pp::generateParser<" ... grammar...">();

• Plain standard C++-20, no extra dependency
• Supports lalr(1) grammar
• Can parse expressions at compile time!

constexpr auto parseResult=parser.parse<"...text to be parsed">();

Status: the grammar is completely created, parsing is still in progress, no action is issued. Lexer do not track position yet. Compile time features requires wrapping the text in lambda, but we will improve on it.

Based on: The project is based on lalr parser generator by Charles Baker.

See the development notes

Example - outdated

In the following example we show the regex parser in action, detecting a json real number, at compile time

#include <parserGenerator.hpp>

int main()
{
  /// Recognized token
  enum {JSON_NUMBER,JSON_REAL_NUMER,TEXT_NOT_CONTAINING_H};
  
  /// Pattern to recognize a number
  constexpr char jsonNumberPattern[]="(\\+|\\-)?[0-9]+";
  
  /// Pattern to recognize a real number
  constexpr char jsonRealNumberPattern[]="(\\+|\\-)?[0-9]+(\\.[0-9]+)?((e|E)(\\+|\\-)?[0-9]+)?";
  
  /// Pattern to recognize a string not containing char 'h'
  constexpr char testNotContainingHPattern[]="[^h]+";
  
  /////////////////////////////////////////////////////////////////
  
  /// Storage properties of the regex pattern matcher
  constexpr auto specs=estimateRegexParserSize(jsonNumberPattern,jsonRealNumberPattern,testNotContainingHPattern);
  
  /// Regex parser matcher
  constexpr auto parser=createParserFromRegex<specs>(jsonNumberPattern,jsonRealNumberPattern,testNotContainingHPattern);
  
  static_assert(parser.parse("-332.235e-34")==JSON_REAL_NUMER);
  static_assert(parser.parse("33")==JSON_NUMBER);
  static_assert(parser.parse("ello world!")==TEXT_NOT_CONTAINING_H);
  
  return 0;
}