#9980: TcS monad is too heavy -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Description changed by simonpj: Old description:
The typehcecker's constraint-solving monad, `TcS`, is simply built on top of `TcM`, but it doesn't use most of `TcM`'s facilities. That was fine while `TcS` was only called from the typechecker, but now (as part of [wiki:PatternMatchCheck fixing pattern-match overlap checking]) we invoke it from the desugarer.
It seems quite wrong to construct a vast, and unnecessary `TcM` context just to invoke `TcS`.
Better: make `TcS` into its own monad, with its own `TcSLclEnv`, built on `IOEnv` like the others.
Main objection: the plugins mechanism exposes `unsafeTcPluginTcM`, which would become unavailable. But it it used?
New description: The typechecker's constraint-solving monad, `TcS`, is simply built on top of `TcM`, but it doesn't use most of `TcM`'s facilities. That was fine while `TcS` was only called from the typechecker, but now (as part of [wiki:PatternMatchCheck fixing pattern-match overlap checking]) we invoke it from the desugarer. It seems quite wrong to construct a vast, and unnecessary `TcM` context just to invoke `TcS`. Better: make `TcS` into its own monad, with its own `TcSLclEnv`, built on `IOEnv` like the others. Main objection: the plugins mechanism exposes `unsafeTcPluginTcM`, which would become unavailable. But it it used? -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9980#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler