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Understand Monad Transformers

Monad transformer(monadT) is another significant concept in Haskell. To understand the monadT, it's compulsory to know how monad works and the mechanism of >>=(bind). You can view the blog Understand Monad or any popular monads to learn about them.

In this blog, I will convey how we use monad transformer while how we recognize the idea that monad transformer creates a new monad. I will explain the function lift as well.

Fail to Reflect Set During Conversion

This blog records the failure when trying to set the response value using reflect to provide an adaptor for wrapping the original PRC interceptor to the custom interceptor format defined by our tech products.

The difference between them is the custom interceptor moves the response from an argument to a response. This blog introduces the challenges encountered while designing an adaptor.

Signatures of Original RPC Interceptor And Custom Interceptor 
// package rpc
// original RPC interceptor signature
type Interceptor func(ctx context.Context, 
    request, response interface{}, processor Processor) uint32
type Processor func(ctx context.Context, request, response interface{}) uint32


// package custom
// interceptor in the tech team
type CustomInterceptor interface {
    Wrap(HandlerFn) HandlerFn
}
type HandlerFn func(ctx context.Context, req interface{}) (interface{}, error)

Understand Monads

Monad is a fundamental concept in Haskell. Recently, I have reviewed them and made my mind clearer. Hence, I wrote down this blog. To understand them, we need to clearly understand some concepts, such as:

  • understand the do notation syntax sugar and learn about how de-sugar it to >>= format
  • understand the closures after de-sugaring
  • type constructor
  • understand how the >>= deals with the data held inside a monad
  • understand the runMonad function properly
  • clarify the difference between monad in category(math) and the monad in haskell

Setting Up Debugger for Haskell in Vscode

It's not easy as the other languages which owns an IDE so click the button is the only thing need to do. Using Vscode, I installed several plugins and dependencies, then clicked debug button, oops, nothing happened! The debugger bar flashes and disappear, then nothing happened except the confusing people at the front of screen.

To be frank, I gave up several times when I was attacked by such a messy event. However, another afflict when I want to diagnose my program. After plowing in the troublesome problems, I finally set up it successfully. However, it becomes more messy when I changed my Desktop from Intel to M1, which means I need to set it up AGAIN.

This blog records some hints for setting up Haskell Debugger. I hope I will never set it up with so many trouble again.