Multiple system packages in applications

[raviqqe]

Problems

• Currently, Pen doesn't provide any way to use multiple system packages in an application.
• It's especially useful when someone want to leverage existing resources of foreign languages in Pen.
  • For example, applications of HTTP RESTful API servers can utilize an wrapper package of sqlx, the asynchronous database library in Rust along with the standard os package.

Solution

• Provide a way to use multiple system packages in an application.
• As we cannot provide a single MainFunction type anymore, we might need to generate one in some way.
  • One way to do this is to choose the first system package's return types as the ones for applications' main functions.
  • Another way is simply using none for the return type of main functions.
    • System packages need to provide a way to "exit" from programs with errors just like the exit system call.
    • Users of those system packages are expected to call those functions at the very top level which is in or close to main functions.
  • Related to Removal of `MainFunction` types #549

Changes to pen.json format

{
  "dependencies": {
    "build": {
      "Os": "pen:///os",
      "SqlX": "git://github.com/raviqqe/sqlx-pen"
    },
    "system": ["Os", "SqlX"],
  }
}

Examples

import Os'Context
import SqlX'Context

main = \(osCtx Os'Context, sqlXCtx SqlX'Context) number {
  ...

  0
}

[raviqqe]

Implemented in #744.