Nemerle
From Wikipedia, the free encyclopedia
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| Paradigm: | multi-paradigm: functional, object-oriented, imperative |
|---|---|
| Designed by: | Kamil Skalski, Michał Moskal, Prof. Leszek Pacholski and Paweł Olszta at Wrocław University |
| Typing discipline: | static, strong, inferred |
| Major implementations: | Nemerle |
| Influenced by: | C#, ML |
Nemerle is a high-level statically-typed programming language for the .NET (see also Mono) platform. It offers functional, object-oriented and imperative features. It has a simple C#-like syntax and a powerful metaprogramming system.
It has been named after the mage Nemmerle from "A Wizard of Earthsea" by Ursula K. Le Guin (spelling with a single m is a design decision).
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[edit] Features
Probably the most important feature of Nemerle is the ability to mix object oriented and functional programming styles. The top-level program structure is object oriented, while in the body of methods one can (but is not forced to) use functional style. This is very handy in some programming problems. The feature set here include functional values, variants and pattern matching.
Another very important feature is taking a high-level approach in all aspects of the language—trying to lift as much of the burden from the programmer as possible. Features like macros and type inference fit here.
Features that come from the functional land are variants (aka algebraic data types), pattern matching, type inference and parameter polymorphism (aka generics). The metaprogramming system allows great compiler extensibility, embedding domain specific languages, partial evaluation and aspect-oriented programming.
Last but not least, the usage of more mundane library stuff from the .NET is as easy as (or easier than) in C#.
[edit] Examples
[edit] Hello, World!
The traditional "Hello World!" can be implemented in a more C#-like fashion:
class Hello {
static Main () : void {
System.Console.WriteLine ("Hello, world!");
}
}
or more simply:
System.Console.WriteLine("Hello, world!");
[edit] Examples of macros
Macros allow you to have boilerplate code generated for you under the hood, with additional static checks performed by the compiler. They give you the power to programatically generate code.
[edit] Database accessibility
For example, using Nemerle macros for SQL you can write:
ExecuteReaderLoop ("SELECT firstname, lastname FROM employee WHERE firstname = $myparm", dbcon,
{
System.Console.WriteLine ("Name: {0} {1}", firstname, lastname)
});
instead of
string sql = "SELECT firstname, lastname FROM employee WHERE firstname = :a";
NpgsqlCommand dbcmd = new NpgsqlCommand (sql, dbcon, dbtran);
dbcmd.Parameters.Add("a", myparm);
NpgsqlReader reader = dbcmd.ExecuteReader();
while(reader.Read()) {
string firstname = reader.GetString (0);
string lastname = reader.GetString (1);
System.Console.WriteLine ("Name: {0} {1}", firstname, lastname)
}
reader.Close();
dbcmd.Dispose();
and this is not just hiding some operations into a library, but additional work performed by compiler to understand the query string, variables used there, and columns returned from the database. The ExecuteReaderLoop macro will generate code roughly equivalent to what you would have to type manually. Moreover, it connects to the database at compilation time to check that your SQL query really makes sense.
[edit] New language constructs
With Nemerle macros you can also introduce some new syntax into the language:
macro ReverseFor (i, begin, body)
syntax ("ford", "(", i, ";", begin, ")", body)
{
<[ for ($i = $begin; $i >= 0; $i--) $body ]>
}
defines a macro introducing the ford (EXPR ; EXPR) EXPR syntax and can be used like
ford (i ; n) print (i);
[edit] Nemerle with ASP.NET
Nemerle can be either embedded directly into ASP.NET:
<%@ Page Language="Nemerle" %>
<script runat="server">
Page_Load(_ : object, _ : EventArgs) : void {
Message.Text = $"You last accessed this page at: $(DateTime.Now)";
}
EnterBtn_Click(_ : object, _ : EventArgs) : void {
Message.Text = $"Hi $(Name.Text), welcome to ASP.NET!";
}
</script>
<html>
<body>
<form runat="server">
Please enter your name: <asp:TextBox ID="Name" runat="server" />
<asp:Button OnClick="EnterBtn_Click" Text="Enter" runat="server" />
<p><asp:Label ID="Message" runat="server" /></p>
</form>
</body>
</html>
...Or stored in a separate file and entered with a single line:
<%@ Page Language="Nemerle" Src="test.n" Inherits="Test" %>
[edit] 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:
using System;
using System.Runtime.InteropServices;
class PlatformInvokeTest
{
[DllImport("msvcrt.dll")]
public extern static puts(c : string) : int;
[DllImport("msvcrt.dll")]
internal extern static _flushall() : int;
public static Main() : void
{
_ = puts("Test");
_ = _flushall();
}
}
[edit] See also
- Boo - another object oriented, statically typed programming language for the .NET framework, similar to Python.
