#11035: Add implicit call-stacks to partial functions in base -------------------------------------+------------------------------------- Reporter: gridaphobe | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 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 gridaphobe): Regarding problem (1): I get the feeling this will require code duplication at the source level, which would be a Bad Thing. We can't just write {{{#!haskell foldr1 :: (?callStack :: CallStack) => ... foldr1 = faster_foldr1 faster_foldr1 :: ... faster_foldr1 f [] = error faster_foldr1 f (x:xs) = foldr f xs }}} because the call to `error` in `faster_foldr1` won't see a given CallStack, and the chain will be broken there. Instead we'd have to write {{{#!haskell foldr1 :: (?callStack :: CallStack) => ... foldr1 f [] = error foldr1 f (x:xs) = foldr f x xs faster_foldr1 :: ... faster_foldr1 f [] = error faster_foldr1 f (x:xs) = foldr f xs }}} It may be the case that most partial functions in base are either simple themselves (like `head`) or have simple definitions in terms of a total function (like `foldr`). So maybe the duplication wouldn't be ''that'' bad, but I'm still pretty wary of this route... A more heavyweight solution could be to have GHC generate a callstack-free version of each function that takes a CallStack, along with a RULE like you described. Then the source-level duplication is gone, but the desugarer or simplifier becomes more complex. In either scenario we end up exporting multiple versions of the "same" function, which will bloat library sizes. But maybe that's not so bad, the binaries shouldn't be affected. (I kinda like the `PartialFunction` constraint too, it's cute.) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11035#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler