Strange boo language syntax

Question

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

setter = { value | a = value }

What does the | operator mean?

Answer 1

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

Answer 2

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.