#13906: ApplicativeDo doesn't handle existentials as well as it could -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.0.1 Resolution: | Keywords: ApplicativeDo Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by dfeuer): Replying to [comment:3 simonmar]:
Right, but we only need to ensure that a strict pattern match is bound by a `>>=`.
Ah, now I see what you're saying! I was misled by the fact that `b` and `d` are applied to `x1` and `x2`. What you were getting at is that by simply making the very next action "dependent" on a strict pattern match, you propagate strictness from the result level to the action level and rely on the fact that strict monads have `undefined *> a = undefined`. Does that hold up for reader, for example? It doesn't for lazy `State`, but the latter isn't strictly law-abiding, so you're in the clear there. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13906#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler