[racket] Meaning of "@" notation in TR

This is a DeBruijn index for the binding of the type parameter.
-Ian
----- Original Message -----
From: "Jordan Johnson" <jmj at fellowhuman.com>
To: users at racket-lang.org
Sent: Thursday, October 18, 2012 6:50:46 PM GMT -05:00 US/Canada Eastern
Subject: [racket] Meaning of "@" notation in TR


Hi all, 


I'm puzzled by this cryptic notation in Typed Racket (copied from the docs): 


( λ: ( [ x : Number ] ) x ) 


- : (Number -> Number : ((! False @ 0) | (False @ 0)) (0)) 




What does the "@ 0" mean? I have searched all of the TR doc pages, but I see no explanation. 


Thanks, 
jmj 


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