Cool, will check it out!

There are lot of recommended books about a selection of languages regarded as more powerful/expressive/safer than the mainstream, but there's not so much good information about APL, I don't think. Every now and then, I hear different people give a hint about APL's power (not too noisily though... as if they did not want to completely give away the secret :).

I keep wondering what problems are good fit for it. From far it doesn't look like a general purpose PL. To my untrained eyes it looks like some sort of query language that you can somehow bend into doing other things (in the same vein you can use SQL to render the Mandelbrot set [1] :).

And then there's the whole clones/successors/spin offs situation. If I were to learn APL today, I wouldn't even know were to start. ELI looks like a good candidate.

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1: http://wiki.postgresql.org/wiki/Mandelbrot_set

There's GNU APL as a free APL implementation. As for learning APL... It's essentially learning what all its symbols do (there are some references for free online from the vendors of paid APLs, just avoid reading about their extensions,) even Wikipedia's page about APL works as a fast reference. I just use it to play around with numbers (yes, I also wrote a Mandelbrot set with it, a one liner that fits in a tweet,) and I'm trying to enhance a little its usability with a iPython-like in-browser "REPL" specially suited for my uses.