ambition on Ruby's not ready

It is supposed to work this way for some good reasons. But! Enough people have had the same problem as you that new versions of Ruby behave the way you expect.

raganwald 18y

Help me understand: what are the good reasons for the parameters of a block overwriting variables in an enclosing scope?

That is, we are talking about:

    i = 100
    x = 0
    [1,2,3].each { |i| x += i }

I understand why it is incredibly helpful for x to refer to a variable in the enclosing scope (even if we could accomplish this same effect with a fold). What are the use cases for the parameter i referring to a variable in the enclosing scope?

brlewis 18y

As someone who's used to Scheme (lexical scoping), I have to say that's pretty bizarre.

That's my second disappointment with Ruby blocks. The first was learning you could only have one block argument.

Do they resemble first-class objects at all? Can you assign a variable to a block? If you were to assign

  { |i| x += i }

to a variable outside that enclosing scope, and then used that variable in that scope, would i be overwritten in that call to the block?

raganwald 18y

"you could only have one block argument"

Do you mean one method can only have one block?

brlewis 18y

Having only read about Ruby and not coded in it, I'm not sure what the correct terminology is. I'm talking about doing something like this:

  someObject.someMethod({block1},{block2})

tptacek 18y

You can't pass more than one block literal to a method. But you can certainly pass multiple blocks; they're objects, just like anything else. Just add the token "lambda" to your expression:

   def foo(x, y); x.call(y.call); end
   foo(lambda {|x| 2+x}, lambda {1})  # => 3

It seems to me that in this case, the language degrades to approximately the same level as Common Lisp.

brlewis 18y

It's good to see that an upgrade to approximately the power of CL is possible in this case. Still, I feel a little let down. When I first saw Ruby block literals, I said to myself, "Hey, that's a great, concise syntax for lambda. Languages really are getting more lisp-like all the time." But now I know that Ruby block literals aren't really lambda. It does look like Ruby lambdas really are lambdas, though.

mdemare 18y

Blocks are lambda's, they're just not objects (but they can be converted to objects.)

brlewis 18y

If you can't pass more than one block literal to a method, then a block literal is not a real lambda, from the Lisp point of view.

tptacek 18y

This is confusing, because Lisp doesn't have the literal notation you're talking about. Since Ruby supports arbitrary lambdas using "lambda" notation (something Python does not support), it seems like Ruby's syntax can only be be better than Lisp's in this regard.

brlewis 18y

Programming languages should be designed not by piling feature on top of feature, but by removing the weaknesses and restrictions that make additional features appear necessary. I do not think Ruby is better for having an additional syntax (block literals) that is just like an existing syntax (lambda) only more restricted.

tptacek 18y

The syntax isn't meant to be "a better lambda". The syntax is meant to recast other language functions, like looping and iteration, in terms of messages and anonymous functions. Since idiomatic Ruby basically never has "for" loops, despite their easy availability in the language, I'm going to go ahead and call the "block" expiriment successful.

brlewis 18y

If it's meant to recast certain language functionality in terms of anonymous functions, why didn't they just make block literals return anonymous functions? It still strikes me as an almost-could-have-been-great syntax.

Idiomatic Scheme basically never has "do" loops, despite their being part of the core standard, and it's been that way for decades.

tptacek 18y

I agree that block syntax should semantically result in expression evaluating to a Proc object. This would be great:

  y = {|x| x} # => #<Proc>

I agree that block syntax could therefore be greater than it is.

I disagree that you can fairly knock Ruby for this, since blocks and implicit block arguments are still better than what you get in other languages.

brlewis 18y

Could you give a more complete example? I'm getting sane behavior in Ruby 1.8.6:

  irb(main):010:0> f = lambda { i = 100; x = 0; [1,2,3].each { |i| x += i }; x}
  => #<Proc:0x05011b34@(irb):10>
  irb(main):011:0> f.call()
  => 6

raganwald 18y

you missed the fun:

    macbook-pro-2:trunk raganwald$ ruby -v
      => ruby 1.8.6 (2007-03-13 patchlevel 0) [i686-darwin8.10.1]
    macbook-pro-2:trunk raganwald$ irb
    irb(main):001:0> lambda { i = 100; x = 0; [1,2,3].each { |i| x += i }; i }.call
      => 3

ambition 18y

Oh, you're right, I had missed that. Yeah, that's dumb. I can't think of any iterators that would leave useful information in the parameters, either.

Comments