Notes from clerb meeting on Thursday, July 17th

DimpleDough provided a great location for this month’s Cleveland Ruby Users Group and they even shelled out for dinner. We heard a really good talk about about ruby and F#.

The ruby material covered some neat corners of the language like the method_missing method, which operates like python’s getattr. Here’s a toy example of how it can be used:

irb(main):005:0> class C
irb(main):006:1> def foo
irb(main):007:2> 1
irb(main):008:2> end
irb(main):009:1> end
=> nil
irb(main):010:0> c =
=> #
=> 1
irb(main):012:0> class C
irb(main):013:1> def method_missing(m, *args)
irb(main):014:2> puts "you tried to call a method #{m}"
irb(main):015:2> end
irb(main):016:1> end
=> nil
irb(main):017:0> c.baz
you tried to call a method baz
=> nil

Incidentally, note how I added a new method to class C after I originally defined it. That’s a cute trick in ruby. I can imagine a lot of nasty misuses of that, but I think the “we’re all consenting adults” rule should apply. And when a class has dozens of methods, it might be helpful to divide them across different files.

We talked about currying as well, in the context of F#. I tend to use currying in this scenario:

  • I recognize that two separate functions could be refactored to be a single function with a whole bunch more parameters;
  • I remake the original functions as curried versions of the new super function.

In other words, if I already have two methods, like paint_it_red(it) and paint_it_green(it), it’s trivial to realize I could write a paint_it_some_color(it, color) and then replace the original paint_it_red with a curried version.

I found this really useful when it isn’t just a single parameter I’m fixing to a constant value, but maybe a whole bunch.

Apparently, Ruby will add currying support in 1.9. I tried to see if I could “fake it” in the irb interpreter, but I just made a mess:

irb(main):036:0> def f(a, b)
irb(main):037:1> a + b
irb(main):038:1> end
=> nil

Nothing interesting so far. f adds its two parameters. So now I’m going to try to make a new function that returns a version of function f with the first parameter a set to fixed value:

irb(main):046:0> def curried_f(a)
irb(main):047:1> def g(b)
irb(main):048:2> a+b
irb(main):049:2> end
irb(main):050:1> return g
irb(main):051:1> end
irb(main):053:0> curried_f(1)
ArgumentError: wrong number of arguments (0 for 1)
from (irb):50:in `g’
from (irb):50:in `curried_f’
from (irb):53
from :0

The problem (I think) stems from how in Ruby, if I just type the name of the function, the function gets called. So in line 50, when I’m trying to return a reference to the new function I just created, Ruby evaluates the result of calling g without giving it any parameters.

I bet I’m doing something very un-ruby-tastic with this approach. I’m probably supposed to leverage those anonymous blocks instead.

F# looks really interesting. It supports all those weird prolog/erlang/haskell-style features like single assignment, pattern matching, and optimal tail-call recursion, with the benefit of having access to the .NET libraries as well.

One of the best professors I studied under made a remark that in COBOL, you think for five minutes and then type for two hours, but in prolog, you think for two hours, and then type for five minutes. I agree. I have learned a lot of languages, but I haven’t gotten any smarter. I’m just learning how to map my thoughts into notation much more quickly.

I would love to have the time and reason to do a project with F#. I think I’ll start by installing mono and messing around.

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