Error no block given when used yield inside a block - ruby

Question

I'm getting this error
LocalJumpError: no block given (yield)
from fops.rb:52:in `block (2 levels) in gen_list'
from /home/phanindra/.gem/ruby/1.9.1/gems/mp3info-0.6.18/lib/mp3info.rb:306:in `open'
from fops.rb:51:in `block in gen_list'
from fops.rb:46:in `each'
from fops.rb:46:in `gen_list'
from fops.rb:48:in `block in gen_list'
from fops.rb:46:in `each'
from fops.rb:46:in `gen_list'
from fops.rb:48:in `block in gen_list'
from fops.rb:46:in `each'
from fops.rb:46:in `gen_list'
from fops.rb:48:in `block in gen_list'
from fops.rb:46:in `each'
from fops.rb:46:in `gen_list'
from (irb):2
from /usr/bin/irb:12:in `<main>
when used yield inside another block which is inside a begin statement which is inside a if statement,
for a simple understanding here is the prototype
def test
if 1 then
begin
test2(5) do |x|
yield x
end
rescue
end
end
end
def test2(n)
n.times do |k|
yield k
end
end
test() do |y|
puts y
end
The problem is there is no error with the prototype, it worked fine so I dont understand why I'm getting this error, here is my actual code
require "mp3info"
module MusicTab
module FOps
def self.gen_list(dir)
prev_pwd=Dir.pwd
begin
Dir.chdir(dir)
rescue Errno::EACCES
end
Dir[Dir.pwd+'/*'].each{|x|
if File.directory?(x) then
self.gen_list(x)
else
begin
Mp3Info.open(x) do |y|
yield "#{y.tag.title},#{y.tag.album},#{y.tag.artist},#{x}"
end
rescue Mp3InfoError
end
end
}
Dir.chdir(prev_pwd)
end
end
end
I was testing this code using irb
[phanindra#pahnin musictab]$ irb
irb(main):001:0> load 'fops.rb'
/usr/share/rubygems/rubygems/custom_require.rb:36:in `require': iconv will be deprecated in the future, use String#encode instead.
=> true
irb(main):002:0> MusicTab::FOps.gen_list('/fun/Music') do |l|
irb(main):003:1* puts l
irb(main):004:1> end
Any help?
regards

Answer 1

The problem is that you are calling gen_list recursively and at the call site for the recursive descent there really is no block.
What you can do is either:
capture the block as a proc with a & parameter and then forward it, or
add a block that does another yield to the recursive call
So...
def f1 x, &block
block.call(x)
if x > 0
f1 x - 1, &block
end
end
# ...or...
def f2 x
yield x
if x > 0
f2 x - 1 do |y|
yield y
end
end
end
f1 2 do |q|
p ['b1', q]
end
f2 2 do |q|
p ['b2', q]
end