Skip to content
Snippets Groups Projects

fromJust has no HasCallStack

    • Closed Issue created by Joachim Breitner @nomeata

    The function Data.Maybe.fromJust does not have a HasCallStack constraint. I wonder why – is that intentional, or did just nobody bother yet?

    Trac metadata
    Trac field Value
    Version 8.4.3
    Type FeatureRequest
    TypeOfFailure OtherFailure
    Priority normal
    Resolution Unresolved
    Component Core Libraries
    Test case
    Differential revisions
    BlockedBy
    Related
    Blocking
    CC
    Operating system
    Architecture
    To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information

    Child items 0

    • No child items are currently assigned. Use child items to break down this issue into smaller parts.

    Activity

    • Joachim Breitner changed milestone to %8.6.1

      changed milestone to %8.6.1

    • Joachim Breitner changed weight to 5

      changed weight to 5

    • Joachim Breitner added Tfeature request Trac import core libraries labels

      added Tfeature request Trac import core libraries labels

    • Ben Gamari
      Ben Gamari @bgamari ·
      Maintainer

      When HasCallStack was introduced we intentionally did not introduce constraints to partial functions, no matter how small. IIRC this was in part because we expected third-party libraries to fill this need and in part it was out of concern for performance (since you would incur the cost of an additional argument, and potentially allocation, if the function isn't inlined). However, at this point it seems like HasCallStack is pretty well-accepted. It seems to me that we could start considering slowly adding HasCallStacks around in functions that are either (a) nearly certain to inline, or (b) not performance critical.

    • Eric Seidel
      Eric Seidel @gridaphobe ·
      Reporter

      There were also concerns about API stability, particularly since the original implementation exposed the implicit parameter. Now that we have the HasCallStack alias and a decent set of API functions around it, we could swap out the implementation, if necessary, with less potential for client breakage.

      I'd support starting to add HasCallStack constraints to common partial functions like fromJust, head, etc. Though, is this something that should be discussed with the Core Libraries Committee?

    • Artem Pelenitsyn
      Artem Pelenitsyn @ulysses4ever ·
      Reporter

      Does it make sense to mark this one newcomer?

    • Ben Gamari
      Ben Gamari @bgamari ·
      Maintainer

      Sure, this seems like a good task for a newcomer.

      However, I should emphasize to that we don't want to simply scatter HasCallStacks on every partial function. We should be thoughtful and deliberate (and probably consult with the CLC) when making changes like this.

    • Ben Gamari added newcomer label

      added newcomer label

    • Richard Eisenberg
      Richard Eisenberg @rae ·
      Developer

      I really like GHC's internal HasDebugCallStack, which disappears (that is, becomes ()) when DEBUG is not defined via CPP and becomes HasCallStack when DEBUG is defined. As far as I know, there's no standard way to mark a build meant for debugging, but perhaps there should be. Then, we could do the same for all applications instead of just GHC.

    • chessai
      chessai @chessai ·
      Developer

      I really like GHC's internal HasDebugCallStack, which disappears (that is, becomes ()) when DEBUG is not defined via CPP and becomes HasCallStack when DEBUG is defined. As far as I know, there's no standard way to mark a build meant for debugging, but perhaps there should be. Then, we could do the same for all applications instead of just GHC.

      In addition to making this available to users of GHC, there should probably be an additional side-effect to the DEBUG flag, or a separate flag, that turns HasDebugCallStack on for all functions

    • Ben Gamari
      Ben Gamari @bgamari ·
      Maintainer

      We already have a very similar mechanism for Control.Exception.assert occurrences at compile-time. It would be reasonably straightforward to add a similar flag for a magic synonym of HasCallStack.

    • Fangyi Zhou
      Fangyi Zhou @fangyi-zhou ·
      Trac metadata
      Trac field Value
      Differential revisions - → D5256
    • Fangyi Zhou mentioned in commit 614028e3

      mentioned in commit 614028e3

    • Ben Gamari closed

      closed

    • Ben Gamari
      Ben Gamari @bgamari ·
      Maintainer

      fangyizhou may look into proposing adding more HasCallStacks elsewhere but this one is finished.

      Trac metadata
      Trac field Value
      Resolution Unresolved → ResolvedFixed
    • Ben Gamari changed milestone to %8.8.1

      changed milestone to %8.8.1

    • Ben Gamari added Pnormal label

      added Pnormal label

    • Luo Chen mentioned in merge request !1551

      mentioned in merge request !1551

    Please register or sign in to reply