Hello Cafe,
Thanks to all of you who provided ideas and suggestions for introducing Haskell. I finally went the simple way, presenting the "knapsack" problem slightly reframed using tapas (spanish dishes). This problem is small enough to fit in the 5 minutes time-frame and it actually illustrates some of the salient points of the langauge: laziness of course, list-comprehensions, monadic computations (replicateM), first-class and higher-order functions, the REPL, integration with emacs, command-line compiling.

Here is the code https://gist.github.com/1948301

I got a lot of positive feedback during the evening as I did some more live coding on simple problems (fizz-buzz, fibonacci) and I ended up showing some code I wrote doing "real stuff", notably the simple music synthesizer I wrote (https://github.com/abailly/haskell-synthesizer) for presenting Haskell to Paris Scala user Group and inspired of course by Paul Hudak's book and Joao Pizani's blog (http://joaopizani.hopto.org/en/2012/01/haskell-synth/). The meeting ended with an impromptu panel on the disadvantages of the languages presented by each speaker which was really hard for me given the sheer perfection of Haskell.

One advantage I mentionned somewhat indirectly which I should stress here is the Haskell community: reactive, vibrant and kind are a few adjectives that spring to my mind.

Thanks again for your support,
Arnaud Bailly