Ruby’s Most Underused Keyword

Re:Ruby’s Most Underused Keyword by petercooper on Saturday February 07, 2009 @04:13AM (#470985)

redo, in the Fibonacci example, is still iterative - it's presented as a third way, when it's just a cruftier way of being iterative. If you remove the cruft of the lambda and the redo, you end up with:

  def fib(i)
    n, result = 1, 0
    while i != -1
      i, n, result = i - 1, n + result, n
    end
    result
  end

Cleaner, faster (by 10% on Ruby 1.8) and shorter, but certainly iterative.

(Separate to this, the fib routines shown produce incorrect results - my example above maintains this, just for comparison with the original code. fib(10) is 55 not 89 - it's one off in its input.)

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Re:Ruby’s Most Underused Keyword by judofyr on Saturday February 07, 2009 @09:15AM (#471126)

You are absolutely right... if you're an interpreter...

From a user's point of view, the redo says "run this block again"; and since the block == the method it's just another way to run acc(). Of course, it's still faking, but I've never claimed anything else :-)

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Re:Ruby’s Most Underused Keyword by petercooper on Saturday February 07, 2009 @10:08AM (#471156)

Since we're having the discussion in two places, I'll be quicker here.. ;-)

"run this block again" signifies "loop" to me and "loop" signifies "iteration." If I see a block of code being looped, I don't think (as a coder, not as an interpreter) that it's recursive. Perhaps others would, though. If we got in a time machine back to the 80s, I kinda feel that "redo" would turn into "goto".. :)

(Hey, we should be doing this on RubyFlow as well - you could be earning some serious karma :))

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Re:Ruby’s Most Underused Keyword by DougBTX on Saturday February 07, 2009 @04:19PM (#471505)

Simplistically, tail call optimisation is an automated way to convert recursion into iteration. You could do that by hand for any tail call recursive function, whether you do so is a function of style and the language you are using.

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