Erlang Riddle for Rubists

The next "Erlang made stupid simple for Ruby programmers" post & screencast is in the making. I am reading again and again the pages of Software for a Concurrent World and try to synthesize Erlang's essence for the "average" Rubist.

Some stuff is straight forward, like Funs which is the Erlang Funny name for Anonymous functions.

ERLANG:

1> Z = fun(X) -> 2*X end.

#Fun

2> Z(2).

4

3> Double = Z.

#Fun

4> Double(4).

8

5> Double(4).

8

RUBY:

irb(main):004:0> Z = Proc.new { |x| x*2 }

=> #

irb(main):005:0> Z.call(2)

=> 4

irb(main):006:0> Double = Z

=> #

irb(main):007:0> Double.call(2)

=> 4

Great stuff, never had to use it in Ruby - but maybe in Erlang it might serve me, who knows....

Now that is an easy one. Later in the book, Joe Armstrong gives an example of a function that returns all permutations of a given string.

perms([]) -> [[]];

perms(L) -> [[H|T] || H <- L, T <- perms(L--[H])].

I have tried to rewrite it in Ruby, in a form that would mostly imitate what's done here.

That's my best try so far:

def prem(s,nx = [])

return nx.join if s.empty?

s.collect { |b| prem(s-[b],nx+[b]) }.flatten

end

puts prem('dor'.split(//))

output:

dor

dro

odr

ord

rdo

rod

I hate the flatten hack I did there to simulate Erlang's valuse return as one Array.

I dislike having to send prem all his recursive "past" (as "nx").

I think there must be a better way to do it. A better way that will deliver the Erlangian concepts.

Do you think you might have a better way to pronounce the Erlangian magic of this function in Rubish ? If so, please post it here (as a comment) I'd really love to see it!

Whoever has a better solution (me need to like) will get full credits and endless honor (!)