Nemerle Language

Nemerle is a new hybrid (functional, object-oriented and imperative) programming language for the .NET platform. It tries to combine the featureset of MlLanguage with a syntax familiar to C/C++/C#/Java programmers.

Key features of the language include:

• simplicity
• C#-like syntax
• easy to use object system (derived directly from the .NET)
• easy access to both functional and imperative features
• powerful code-generating macros
• variants
• pattern matching
• static and on-demand dynamic typing
• type inference.

http://nemerle.org

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For an example of the flavour of the language, here are a few example programs:

HelloWorld:

 module Hello {
     Main(): void {
         Nemerle.IO.printf("Hello world\n"); //System.Console.WriteLine?() would work, too
     }
 }

or a graphical version, using Gtk#:

 using System;
 using Gtk;
 using GtkSharp;

 module hello {
     Main(): void {
         Application.Init();

         def button = Button("Hello World");
         button.Clicked += (fun(_,_) {
             Console.WriteLine("Hello World")
         }); // extra parentheses around the anonymous function unfortunately
             // necessary due to a tweak that was made to keyword precedences
             // in version 0.1.4. This issue is being reconsidered, however,
             // and may be changed back at some point.

         def window = Window("Helloworld");
         window.DeleteEvent += (fun(_,_) {
             Application.Quit()
         });

         window.Add(button);
         window.ShowAll();
         Application.Run()
     }
 }

And something a little more complex - a macro definition, for an alternative exception-handling syntax (based [very roughly] on the syntax presented in http://research.microsoft.com/~akenn/sml/ExceptionalSyntax.pdf):

 macro AttemptUnless(tryexpr, catchexpr, exc: funparm, thenexpr)
 // would be "try" instead of "attempt", but the current macro system is
 // unable to disambiguate between multiple syntactic forms using the
 // same keywords, and try is already taken by the normaltry-catch-finally
 // exception-handling syntax
 syntax("attempt", "(", tryexpr,")",
        "catch", "(", exc, ")", catchexpr,
        "else", thenexpr) {
     match(tryexpr) {
     | <[$(nm: name) = $attempt]> =>
         match(exc) {
         | <[ funparm: $(exc: name): $ty ]> =>
             <[
             mutable $(exc: name) = null;
             def $(nm: name) =
                 try { Some($attempt) }
                 catch {
                     exception: $ty => $(exc: name) = exception; None ()
                 }
             match($(nm: name)) {
             | Some($(nm: name)) => $thenexpr
             | None => $catchexpr
             }
             ]>
         | _ => Message.fatal_error("oops")
         }
     | _ => Message.fatal_error("d'oh!")
     }
 }

This allows things like this:

 public static Collect(fileNames : list <string>) : string {
 | [] => ""
 | fileName :: rest =>
     attempt (f = File.OpenText (fileName))
     catch(ex : Exception) {
         Log (ex);
         Collect (rest);
     }
     else {
         def s = f.ReadToEnd ();
         f.Close();
         s + Collect (rest)
     }
 }

Where the else block is only executed when File.OpenText() doesn't throw. The full code it expands out to is roughly:

 public static Collect(fileNames : list <string>) : string {
 | [] => ""
 | fileName :: rest =>
     mutable ex = null;
     def f = try { Some (File.OpenText (file_name)) }
             catch { e : Exception => ex = e; None () }
     match(f) {
     | Some(f) =>
         def s = f.ReadToEnd ();
         f.Close ();
         s + Collect(rest)
     | None =>
         Log(ex);
         Collect(rest)
     }
 }

There's currently [September 2004] some discussion on the nemerle wiki [http://nemerle.org/cgi-bin/wiki/NemerleWiki] (which is otherwise somewhat quiet, unfortunately) (and on the mailing list, which is somewhat more active), about the best choice of syntax for this kind of construct: http://nemerle.org/cgi-bin/wiki/TryUnlessFeedback

The macro above was just something I hacked together (and later improved, to use Nemerle's option type (the Some(a) and None() bits in the macro above - equivalent to the Haskell Just a and Nothing), after I realised it didn't work with value types) to see if I could do it - the final solution will no doubt be significantly better. (It'll probably have proper error messages, for a start...)

-- MikeRoome

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How about comparisons to ScalaLanguage? Where Scala is basically Java + Functional + syntax, Nemerele is basically CeeSharp + Functional + Syntax. However, they do have distinct features.

Scala:

• Singletons with object Foo {} syntax.
• No static methods; singleton methods instead.
• var and val declare mutability, which favors neither.
• ctors baked into class definition, and are ensured to be called (like C++)
• Syntactic monad support.

Nemerele:

• def and mutable declare mutability, favoring immutable values by Huffman coding.
• Macros

Please add more!

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CategoryProgrammingLanguage CategoryFunctionalProgramming