#14255: Type-indexed type fingerprints -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Core Libraries | Version: 8.2.1 Resolution: | Keywords: Typeable Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by dfeuer): Replying to [comment:1 simonpj]:
I'm 100% lost. What is a fingerprint? How do you create them? How does it reduce the size of the TCB?
A fingerprint is just a number (a sort of hash) assigned to a type. Fingerprints are used to allow fast comparisons between `TypeRep`s. But they're not really attached to the types they represent, and the unsafe bits of handling them are woven into the larger/more complex `TypeRep` code. I hypothesize that we could compact, if not technically reduce, the TCB by using a separate module for a simple newtype {{{#!hs newtype FingerprintIx a = FingerprintIx Fingerprint }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14255#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler