Nemerle

Nemerle is a general-purpose, high-level, statically typed programming language designed for platforms using the Common Language Infrastructure (.NET/Mono). It offers functional, object-oriented, aspect-oriented, reflective and imperative features. It has a simple C#-like syntax and a powerful metaprogramming system.

In June 2012, the core developers of Nemerle were hired by the Czech software development company JetBrains. The team was focusing on developing Nitra, a framework to implement extant and new programming languages. Both the Nemerle language and Nitra have seemingly been abandoned or discontinued by JetBrains; Nitra has not been updated by its original creators since 2017 and Nemerle is now maintained entirely by the Russian Software Development Network, independently from JetBrains, although no major updates have been released yet and development is progressing very slowly. Neither Nemerle, nor Nitra have been mentioned or referenced by JetBrains for years.

Nemerle is named after the Archmage Nemmerle, a character in the fantasy novel A Wizard of Earthsea by Ursula K. Le Guin.

Features
Nemerle's most notable feature is the ability to mix styles of programming that are object-oriented and functional. Programs may be structured using object-oriented concepts such as classes and namespaces, while methods can (optionally) be written in a functional style. Other notable features include:
 * strong type inference
 * a flexible metaprogramming subsystem (using macros)
 * full support for object-oriented programming (OOP), in the style of C#, Java, and C++
 * full support for functional programming, in the style of ML, OCaml, and Haskell, with these features:
 * higher-order functions
 * pattern matching
 * algebraic types
 * local functions
 * tuples and anonymous types
 * partial application of functions

The metaprogramming system allows for great compiler extensibility, embedding domain-specific languages, partial evaluation, and aspect-oriented programming, taking a high-level approach to lift as much of the burden as possible from programmers. The language combines all Common Language Infrastructure (CLI) standard features, including parametric polymorphism, lambdas, extension methods etc. Accessing the libraries included in the .NET or Mono platforms is as easy as in C#.

Variants
Variants (called data types or sum types in SML and OCaml) are forms of expressing data of several different kinds:

Metaprogramming
Nemerle's macro system allows for creating, analysing, and modifying program code during compiling. Macros can be used in the form of a method call or as a new language construct. Many constructs within the language are implemented using macros (if, for, foreach, while, using etc.).

"if" macro example:

Braceless syntax
Similarly to the braceless syntax later added to Scala, Nemerle allows the programmer to optionally use a whitespace-sensitive syntax based on the off-side rule, similarly to Python.

The following curly-brace snippet:

could be rewritten as:

Notably, it is not possible to break expressions or alternative clauses in matches over multiple lines without using a backslash :

In order to activate this syntax, the user must add  to the top of the file or use the compiler option.

IDE
Nemerle can be integrated into the integrated development environment (IDE) Visual Studio 2008. It also has a fully free IDE based on Visual Studio 2008 Shell (like Visual Studio Express Editions) and SharpDevelop (link to plugin source code).

Nemerle can be also integrated into Visual Studio (up until 2017) using add-ins and extensions.

Hello, World!
The traditional Hello World! can be implemented in a more C#-like fashion:

or more simply:

Examples of macros
Macros allow generating boilerplate code with added static checks performed by the compiler. They reduce the amount of code that must be written by hand, make code generation safer, and allow programs to generate code with compiler checks, while keeping source code relatively small and readable.

String formatting
The string formatting macro simplifies variables to string manipulations using $ notation:

Declarative code generation
StructuralEquality, Memoize, json, and with are macros which generate code in compile time. Though some of them (StructuralEquality, Memoize) can look like C# attributes, during compiling, they will be examined by the compiler and transformed to appropriate code using logic predefined by their macros.

Database accessibility
Using Nemerle macros for SQL you can write:

instead of

and this is not just hiding some operations in a library, but additional work performed by the compiler to understand the query string, the variables used there, and the columns returned from the database. The ExecuteReaderLoop macro will generate code roughly equivalent to what you would have to type manually. Moreover, it connects to the database at compilation time to check that your SQL query really makes sense.

New language constructs
With Nemerle macros you can also introduce some new syntax into the language:

defines a macro introducing the ford (EXPR ; EXPR) EXPR syntax and can be used like

ford (i ; n) print (i);

Nemerle with ASP.NET
Nemerle can be either embedded directly into ASP.NET: ...Or stored in a separate file and entered with a single line:

PInvoke
Nemerle can take advantage of native platform libraries. The syntax is very similar to C#'s and other .NET languages. Here is the simplest example: