#14254: The Binary instance for TypeRep smells a bit expensive -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: patch Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.2.1 Resolution: | Keywords: Typeable Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #14337 | Differential Rev(s): Phab:D3998, Wiki Page: | Phab:D4082, Phab:D4085 -------------------------------------+------------------------------------- Comment (by simonpj): Re the loop, `Type` = `TYPE Lifted`. So the `TypeRep` for `Type` is a `TrApp`, with a cached kind. So {{{ TYPE Lifted :: TYPE Lifted }}} But that kind has a cached kind: {{{ TYPE Lifted :: TYPE Lifted :: TYPE Lifted }}} and if the cache field is strict you build an infinite data structure. The only way out of this I can see is to * define a top level definition the `TypeRep` for `TYPE Lifted` * in that definition, do not use `mkTrApp`; instead build an explicit loop {{{ trTYPELifted = TrApp fpr trTYPE trLifted trTYPELifted }}} note that `trTYPELifted mentions itself directly. * In `mkTrApp` spot that case, and return `trTYPELifted`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14254#comment:14 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler