Rails: named_scope, lambda and blocks

it's a parser problem. try this

named_scope :admin, (lambda do |company_id| 
  {:conditions => ['company_id = ?', company_id]}
end)

I think the problem may be related to the difference in precedence between {...} and do...end

There's some SO discussion here

I think assigning a lambda to a variable (which would be a Proc) could be done with a do ... end:

my_proc = lambda do 
  puts "did it"
end
my_proc.call #=> did it

If you're on ruby 1.9 or later ¹, you can use the lambda literal (arrow syntax), which has high enough precedence to prevent the method call from "stealing" the block from the lambda.

named_scope :admin, ->(company_id) do 
  {:conditions => ['company_id = ?', company_id]}
end

^{1 The first stable Ruby 1.9.1 release was 2009-01-30.}

It's something related to precedence as I can tell

1.upto 3 do # No parentheses, block delimited with do/end
  |x| puts x 
end

1.upto 3 {|x| puts x } # Syntax Error: trying to pass a block to 3!