When I read about Paul Graham's Accumulator Generator on Lambda the Ultimate, I tried it in Loell. As it turned out the solution was shorter than any of the solutions on Paul's page, without being complex. So I wrote an e-mail to Paul Graham:

I don't know if you accept personal pet programming languages for your Accumulator Generator. Anyway I hope you are interested in Loell, because the solution seems to be the shortest one yet:

foo={\n;{n+=that}}

To test this go to http://w3future.com/html/loell/ and run this piece of code:

foo={\n;{n+=that}}
 
x = $ foo 1
$ x 5
$ foo 3
$ x 2.3

Actually, because Loell is (meant to be) object-oriented, the functions are methods of the current scope object ($). Method calls always have the format: object methodName argument. That's why the function calls look like the way they do.

Originally the default argument name was "_" like in Arc. I changed it to "that" to match "this" as the name for the left-hand side of a method call. If I hadn't, the solution would have been almost the shortest imaginable: foo={\n;{n+=_}}

Note that there are no tricks involved, it's just that the syntax for closures is so short: {}.