Strange boo language syntax

I've run into a strange syntax in Boo Language Guide :

setter = { value | a = value }

What does the | operator mean?

From stackoverflow Artem Tikhomirov

• Well, having never used Boo, my (educated) guess is that it's for passing parameter to the closure lambda-style functions. In this case, { p | C } refers to an anonymous function taking a single parameter bound to p within the code C.

  From Adam Wright

• The documentation of Boo seems to be lacking in this area -- it seems that

  setter = { value | a = value }
  

  is shorthand for

  setter = def(value):
      a = value
  

  From dF

• Adam is correct. The point of the example is to show that lambdas in boo have read and write access to enclosing scope.

  From Frep D-Oronge

• That syntax for specifying code blocks (anonymous functions) has been borrowed from Ruby and Smalltalk

  From Mauricio Scheffer