Re: [GHC] #13708: Panic! (the "impossible" happened) bug in GHC 8.2.1 rc2

#13708: Panic! (the "impossible" happened) bug in GHC 8.2.1 rc2 -------------------------------------+------------------------------------- Reporter: deech | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: 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 Simon Peyton Jones ): In [changeset:"d6461f9684f6f758320a5e5afbf0634fcc2996a5/ghc" d6461f96/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="d6461f9684f6f758320a5e5afbf0634fcc2996a5" Handle type-lets better Core allows non-recursive type-lets, thus let a = TYPE ty in ... They are substituted away very quickly, but it's convenient for some passes to produce them (rather than to have to substitute immediately). Trac #13708 tried the effect of not running the simplifer at all (a rather bizarre thing to do, but still). That showed that some passes crashed because they always treated a let-bounder binder as an Id. This patch adds some easy fixes. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13708#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler