I want to leverage my visitor pattern source generator to implement a simple minimal api.

I aim to:

• Have a request and a request handler for my endpoint. I will not use mediatr or any similar library and I will not use any real storage, only some in memory data structure to showcase the visitor pattern approach.
• The request handler Handle method returns an interface, every subtype represents a different type of result, a success, and one type for each error (provided) emitted by the handled.
• For each subtype we want to be able to return a possibly different http response.

In a previous experiment I made I used the LLVMSharp library and I was quite curious on how the bindings are made. In the readme is it stated they are generated using che ClangSharp library, this one auto-generate hitself from the headers of Clang C header.

This functionality is exposed through a dotnet tool: ClangSharpPInvokeGenerator. So I wanted to try and hack my way into parsing the tree-sitter headers and use the generated code to run a very small sample using C#, in particular I was aiming for the one that's in the getting started section of the docs

I am a big fan of the visitor pattern, I think it is a very good approach for adding behaviors to a group of classes without modifying all of them.

For example if we are building a compiler we may have an abstract syntax tree that represents the code that the compiler is compiling. Two different visitors can be, for example:

• a type checker
• a code emitter

If you're interested in creating new programming languages or domain specific languages and also in scheme or LISP you will definitively encounter Racket at some point. Which is described on the official website as "the Language-Oriented Programming Language" so it is something to look into it.

In this post we will see how to use EF6 (not EF Core) in a .NET Core application with SQLite. Why we would like to do this? Maybe we are migrating a project from the full framework to .NET Core but we are not ready to migrate also EF6 to EF Core. I will not show how to work with migrations.

First of all, we need to install two packages in our project:

• System.Data.SQLite.EF6
• System.Data.SQLite

In a previous post I talked about ROP in C#, now I want to explore how to use it in a ASP.NET Core web api project. If you haven't I suggest to take a look at my previous posts since I won't go into the details of union types and my custom Result<T> type:

1. A tagged union example
2. Railway oriented programming with C#

What problems does DI solve? I really like what wikipedia says

The intent behind dependency injection is to achieve separation of concerns of construction and use of objects.

If class A needs to use class B, it does not need to create an instance of it. This will give A too much responsibility since beside its actual requirements it has to manage the lifetime of the instance of B.

LLVM Kaleidoscope .NET​

If you're reading and learning about compilers in these days you will at some point find something about LLVM. I did and I tried to implement the Kaleidoscope tutorial from the official documentation using C#. I won't write a full blown tutorial and in the end I didn't actually follow the official tutorial as it was pretty hard for me to read C++ code.

Workflows​

As a software developer I work, most of the times, on LOB applications that support some kind of process or workflow for a specific company. That means that there are some entities, such as customers, orders or support tickets, and that they evolve during the lifecycle of the application. For example we could have a CRM with a lead entity that evolves into a customer or we could track the state of a ticket: open -> analysis -> work -> deploy.

Parsing polynomials with F# and FParsec​

Parsing a polynomial expression is a simple but interesting example of parsing. We need to handle operator precedence and associativity, for example * has a higher precedence than + and the exponentiation is right associative x^y^z=x^(y^z) while subtraction is left associative x-y-z=(x-y)-z. Moreover a straighforward definition of the grammar is left recursive and a recursive descent parser does not allow to parse such grammar. We need to arrange our grammar in order to avoid the left recursion.