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P
Developer	Ankush Desai, Vivek Gupta: not the politician, Ethan Jackson, Shaz Qadeer, Sriram Rajamani, Microsoft
First appeared	2012; 13 years ago
OS	Cross-platform
License	MIT License
Filename extensions	.p
Website	p-org.github.io/P/

P is a programming language for asynchronous event-driven programming and the IoT that was developed by Microsoft and University of California, Berkeley.^[1]

P enables programmers to specify systems consisting of a collection of state machines that communicate asynchronously in terms of events.^[2] P programs can run and be analyzed on any platform supported by .NET. Additionally, P programs can generate C# and C code.

P is open source, licensed under MIT License, and available on GitHub.^[3]

Example

machine BankServer
{
  var database: Database;

  start state Init {
    entry (initialBalance: map[int, int]){
      database = new Database((server = this, initialBalance = initialBalance));
      goto WaitForWithdrawRequests;
    }
  }

  state WaitForWithdrawRequests {
    on eWithDrawReq do (wReq: tWithDrawReq) {
      var currentBalance: int;
      var response: tWithDrawResp;

      // read the current account balance from the database
      currentBalance = ReadBankBalance(database, wReq.accountId);
      // if there is enough money in account after withdrawal
      if(currentBalance - wReq.amount >= 10)
      {
        UpdateBankBalance(database, wReq.accountId, currentBalance - wReq.amount);
        response = (status = WITHDRAW_SUCCESS, accountId = wReq.accountId, balance = currentBalance - wReq.amount, rId = wReq.rId);
      }
      else // not enough money after withdraw
      {
        response = (status = WITHDRAW_ERROR, accountId = wReq.accountId, balance = currentBalance, rId = wReq.rId);
      }

      // send response to the client
      send wReq.source, eWithDrawResp, response;
    }
  }
}