#8450: can't match type Bool with (), but shouldn't have to -------------------------------------+------------------------------------ Reporter: dmwit | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Changes (by simonpj): * cc: dimitris@… (added) Comment: Nice example. (The rest of this is cryptic comments mainly for Dimitrios.) The issue is this. We have a skolem 'a', and two constraints {{{ [w} a ~ Bool [w] a ~ () }}} But because we rewrite wanteds with wanteds, we rewrite to {{{ [w] Bool ~ () }}} which is really quite unhelpful. I'm beginning to wonder: what would happen if we never rewrote a wanted with another wanted? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8450#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#8450: can't match type Bool with (), but shouldn't have to -------------------------------------+------------------------------------ Reporter: dmwit | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by Simon Peyton Jones ): In [changeset:"8c88d0a9b205a31b1708a7069c4aa417373f9ac3/testsuite"]: {{{ #!CommitTicketReference repository="testsuite" revision="8c88d0a9b205a31b1708a7069c4aa417373f9ac3" Test Trac #8450 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8450#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#8450: can't match type Bool with (), but shouldn't have to ------------------------------------------------+-------------------------- Reporter: dmwit | Owner: Type: feature request | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Test Case: typecheck/should_fail/T8450 | Difficulty: Blocking: | Unknown | Blocked By: | Related Tickets: ------------------------------------------------+-------------------------- Comment (by Simon Peyton Jones ): In [changeset:"7881488201629aa1ab36e3e0fbeb4d7b4b85bd91/ghc"]: {{{ #!CommitTicketReference repository="ghc" revision="7881488201629aa1ab36e3e0fbeb4d7b4b85bd91" A raft of changes driven by Trac #8540 The root cause of #8450 is that the new Template Haskell story, with the renamer doing more of the work of Template Haskell, wasn't dealing correctly with the keepAlive problem. Consider g = ..blah... f = [| g |] Then f's RHS refers to g's name but not to g, so g was being discarded as dead code. Fixing this sucked me into a deep swamp of understanding how all the moving parts of hte new Template Haskell fit together, leading to a large collection of related changes and better documentation. Specifically: * Instead of putting the TH level of a binder in the LocalRdrEnv, there is now a separate field tcl_th_bndrs :: NameEnv (TopLevelFlag, ThLevel) in the TcLclEnv, which records for each binder a) whether it is syntactically a top-level binder or not b) its TH level This deals uniformly with top-level and non-top-level binders, which was previously dealt with via greviously-delicate meddling with Internal and External Names. Much better. * As a result I could remove the tct_level field of ATcId. * There are consequential changes in TcEnv too, which must also extend the level bindings. Again, more clarity. I renamed TcEnv.tcExtendTcTyThingEnv to tcExtendKindEnv2, since it's only used during kind inference, for (AThing kind) and APromotionErr; and that is relevant to whether we want to extend the tcl_th_bndrs field (no). * I de-crufted the code in RnEnv.extendGlobalRdrEnv, by getting rid of the qual_gre code which said "Seems like 5 times as much work as it deserves!". Instead, RdrName.pickGREs makes the Internal names shadow External ones. * I moved the checkThLocalName cross-stage test to finishHsVar; previously we weren't doing the test at all in the OpApp case! * Quite a few changes (shortening the code) in the cross-stage checking code in TcExpr and RnSplice, notably to move the keepAlive call to the renamer One leftover piece: * In TcEnv I removed tcExtendGhciEnv and refactored tcExtendGlobalTyVars; this is really related to the next commit, but it was too hard to disentangle. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8450#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler