Functional oriented programming in D

[via Digitalmars-d-learn]

Hi

After a couple of years using and keeping an eye on D I have 
grown into a functional oriented programmer. I began with 
JavaScripts semi pseudo functional style, then Clojures dynamic 
functional style, Haskells burritos and now Scala.

I have began to dislike Haskell for the academic approach to 
programming. To do anything you must think and think again. The 
knowledge you need to code haskell is more than the syntax and 
rules.

Then i thought about D some days ago. Thought Id give it a new 
try. Take a new look. See if something had changed from my side 
or the language. Well certainly from my side given the fact that 
I am no longer an OO programmer. Well i do OO stuff everyday, but 
despise it and remind myself and other devs how this could have 
be done better.

I found that there is std.algorithm, std.functional and lambda 
expressions in D. Thats very interesting. It gives a promise that 
I can use those tools to create (almost) class less programs. I 
initiated a vibe.d project and tried to change the listen handler 
to a lamdba expression:

listenHTTP(settings, (req, res) => res.writeBody("Hello, 
World!"));

And it worked obviously well.

But when I changed it to multiline lambda:

listenHTTP(settings, (req, res) => {
	res.writeBody("Hello, World!");
});

It gave me an error:

[jarl at galifrey vibed-app] $ dub
Target vibe-d 0.7.23 is up to date. Use --force to rebuild.
Building vibed-app ~master configuration "application", build 
type debug.
Compiling using dmd...
source/app.d(8,12): Error: None of the overloads of 'listenHTTP' 
are callable using argument types (HTTPServerSettings, void), 
candidates are:
../../.dub/packages/vibe-d-0.7.23/source/vibe/http/server.d(71,6):        vibe.http.server.listenHTTP(HTTPServerSettings settings, void delegate(HTTPServerRequest req, HTTPServerResponse res) request_handler)
../../.dub/packages/vibe-d-0.7.23/source/vibe/http/server.d(95,6):        vibe.http.server.listenHTTP(HTTPServerSettings settings, void function(HTTPServerRequest req, HTTPServerResponse res) request_handler)
../../.dub/packages/vibe-d-0.7.23/source/vibe/http/server.d(100,6):        vibe.http.server.listenHTTP(HTTPServerSettings settings, HTTPServerRequestHandler request_handler)
FAIL 
.dub/build/application-debug-linux.posix-x86_64-dmd_2067-006B89616986857CBBFCCB1EAEA3E85E/ vibed-app executable
Error executing command run:
dmd failed with exit code 1.

Which I belive means that a single line lambda is a different 
object type than multiline lambda?

Why?