如何使用javascript在函数式编程中使用IO和Either函数实现线性流？

Question

Result: linear flow like getFile(filename).map(parseJson).map(doOtherThings)...

When I'm using Either itself everything is nice and easy

function doSomethingCrazyHere(){
  return "something crazy";
}

function safeUnsureFunction(){
    try{
       return Right(doSomethingCrazyHere());
    }catch(e){
       return Left(e);
    }
}

then I can just do the following

safeUnsureFunction().map((result)=>{
  // result is just result from doSomethingCrazyHere function
  // everything is linear now - I can map all along
  return result;
})
.map()
.map()
.map()
.map();
// linear flow

problem is when I'm using IO like:

function safeReadFile(){
  try{
    return Right(fs.readFileSync(someFile,'utf-8'));
  }catch(e){
    return Left(error);
  }
}

let pure=IO.from(safeReadFile).map((result)=>{
  // result is now Either
  // so when I want to be linear I must stay here
  // code from now on is not linear and I must generate here another chain

  return result.map(IdontWant).map(ToGo).map(ThisWay).map(ToTheRightSideOfTheScreen);
})
.map((result)=>{
  return result.map(This).map(Is).map(Wrong).map(Way);
})
.map(IwantToBeLienearAgain)
.map(AndDoSomeWorkHere)
.map(ButMapFromIOreturnsIOallOverAgain);

let unpure=function(){
  return pure.run();
}

IO is for separating pure from not so pure functions right?

So I want to separate unpure file read with also Either file error handling. Is this possible?

How to have linear flow when using Eithers inside IO monads?

Is there any pattern in functional programming for this?

readFile(filename).map(JSON.parse).map(doSomethingElse)....

Answer 1

Only way for this could be to add safeRun method to the IO so at the end we will have Either and we will gracefully recover from error

class safeIO {
  // ...

  safeRun(){
    try{
      return Right(this.run());
    }catch(e){
      return Left(e);
    }
  }

  //...
}

Instead of safeReadFile that returns Either we must use normal readFile

function readFile(){
    return fs.readFileSync(someFile,'utf-8');
}

let pure = safeIO.from(readFile)
.map((result)=>{
  // result is now file content if there was no error at the reading stage
  // so we can map like in normal IO
  return result;
})
.map(JSON.parse)
.map(OtherLogic)
.map(InLinearFashion);

let unpure = function(){
  return pure.safeRun(); // -> Either Left or Right
}

or take the try catch logic outside an IO to the unpure function itself without modyfing any IO

let unpure = function(){
  try{
    return Right(pure.run());
  }catch(e){
    return Left(e);
  }
}
unpure(); // -> Either