#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):
it should either print plain exception or the call stack that finishes at the library’s API
I would say that `minimumBy`s call stack does "finish at the library's api;" the root is in GHC.List, which is part of base. Perhaps you mean that a function `f` should only print call stacks whose root is `f`. That's an interesting point, and does seem reasonable for production code, but it sounds very non-trivial to implement. You can think of the CallStack solver as rewriting your code as follows. Whenever it sees a CallStack constraint, eg from a call to `error` {{{ f x = error }}} it inserts a new implicit binder that adds the current call-site {{{ f x = let ?callStack = <this-call-site> `pushCallStack` ?callStack in error }}} The `?callStack` on the rhs will either be discharged by the CallStack in `f`s context (if `f` requested one) or by the empty CallStack. So we can't just write `let ?callStack = emptyCallStack in error` because that's effectively what GHC is already doing for us. Instead we would need multiple versions of the callstack-aware functions, as Richard suggested. In general, I think Richard's suggestion of a call-stack scrubbing pass for optimized code should satisfy your concern as well. If I compile packages from hackage with optimizations (the default I think), then I won't see the implementation details. If I don't, I'll see the details, but I can at least submit a more informative bug report! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11035#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler