[Functional Programming] Reader with Async ADT

逃离我推掉我的手 2021-11-17 06:54 276阅读 0赞

> `ReaderT` is a `Monad Transformer` that wraps a given `Monad` with a `Reader`. This allows the interface of a `Reader` that enables the composition of computations that depend on a shared environment `(e -> a)`, but provides a way to abstract a means the `Reader` portion, when combining `ReaderT`s of the same type. All `ReaderT`s must provide the constructor of the target `Monad` that is being wrapped.

The task we want to do is read from a "data.json" file:

{
      "name": "App",
      "config": {
        "prod": "config.prod.json",
        "dev": "config.dev.json",
        "test": "config.test.json"
      }
    }

According to the 'env' variable we pass in, it will pick different config file:

config.test.json:

{
      "port": 5200
    }

In the end, it will output a json file combine the result.

const { readJSON, writeJSON, fork } = require("./helper");
    const {
      Async,
      ReaderT,
      omit,
      pipeK,
      assign
    } = require("crocks");
    
    const ReaderAsync = ReaderT(Async);
    const env = {
      input: "data.json",
      output: "output.json"
    };
    
    const input = env =>
      ReaderAsync(({ input }) => readJSON(input).map(assign({ env })));
    const config = data =>
      ReaderAsync(() =>
        readJSON(data.config[data.env])
          .map(assign(data))
          .map(omit(["config"]))
      );
    const output = inputData =>
      ReaderAsync(({ output }) => writeJSON(output, inputData));
    const flow = pipeK(
      ReaderAsync.of,
      input,
      config,
      output
    );
    
    fork(flow("test").runWith(env));

output.json file:

{
      "port": 5200,
      "name": "App",
      "env": "test"
    }

转载于:https://www.cnblogs.com/Answer1215/p/10957781.html