Wednesday, September 26, 2007

Reading SICP in Erlang and Ruby

I’ve had a long standing goal to read SICP, but it keeps conflicting with other goals, like mastering Ruby or learning Erlang (to name a couple of geeky ones). Recently I learned of a project to ‘translate’ SICP into Erlang (and other languages).

“Great! I can use this to help with both learning Erlang and reading SICP”, I thought and went to take a look at it. It turns out they also have a Ruby translation underway, so I went to look at that first. It turns out that the first couple of examples make me think that they either don’t understand Ruby or don’t understand SICP.

Page 5 of SICP shows that you can start up a LISP or scheme interpreter and type in an expression and it will return that expression, like this:

> 486

The site recommends the following Ruby puts 486, which is not quite right:

irb(main):001:0> puts 486
=> nil

You see, this prints 486, but returns nil. A much better answer looks a lot more like scheme:

irb(main):002:0> 486
=> 486

With a problem like this early on, I’m not sure that I trust the Erlang or other translations. I do like the idea though, so I should probably stick with my idea of combining the goals, and just post my own translations into Erlang and Ruby (and let everyone else find my mistakes).

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