Anything Like Scipy in Ruby

Anything like SciPy in Ruby?

There's nothing quite as mature or well done as SciPy, but check out SciRuby and Numerical Ruby.

Scientific Programming with Ruby

Linear algebra is at the heart of most large-scale scientific computing. LAPACK is the gold standard for linear algebra libraries, first written in FORTRAN.

There's a port to Ruby here. Once you have that, the rest is incidental, but there are also plotting routines in Ruby.

Does Ruby have something like Python's list comprehensions?

The common way in Ruby is to properly combine Enumerable and Array methods to achieve the same:

digits.product(chars).select{ |d, ch| d >= 2 && ch == 'a' }.map(&:join)

This is only 4 or so characters longer than the list comprehension and just as expressive (IMHO of course, but since list comprehensions are just a special application of the list monad, one could argue that it's probably possible to adequately rebuild that using Ruby's collection methods), while not needing any special syntax.

Are there something like Python generators in Ruby?

Ruby's yield keyword is something very different from the Python keyword with the same name, so don't be confused by it. Ruby's yield keyword is syntactic sugar for calling a block associated with a method.

The closest equivalent is Ruby's Enumerator class. For example, the equivalent of the Python:

def eternal_sequence():
  i = 0
  while True:
    yield i
    i += 1

is this:

def eternal_sequence
  Enumerator.new do |enum|
    i = 0
    while true
      enum.yield i # <- Notice that this is the yield method of the enumerator, not the yield keyword
      i +=1
    end
  end
end

You can also create Enumerators for existing enumeration methods with enum_for. For example, ('a'..'z').enum_for(:each_with_index) gives you an enumerator of the lowercase letters along with their place in the alphabet. You get this for free with the standard Enumerable methods like each_with_index in 1.9, so you can just write ('a'..'z').each_with_index to get the enumerator.

What does Ruby have that Python doesn't, and vice versa?

You can have code in the class definition in both Ruby and Python. However, in Ruby you have a reference to the class (self). In Python you don't have a reference to the class, as the class isn't defined yet.

An example:

class Kaka
  puts self
end

self in this case is the class, and this code would print out "Kaka". There is no way to print out the class name or in other ways access the class from the class definition body in Python.

scala: anything like python/ruby development mode?

JRebel, which is the new name for JavaRebel, has a free license for Scala use.

Other alternatives include using Maven's scala:cc target, which keeps compiling on the background, triggered by changes, and, in particular, the Play framework is almost perfect in this regard.

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