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We introduce a new primop `annotateStack#` which allows us to push arbitrary data onto the call-stack. This allows us to extract the data later when decoding the stack, for example when an exception is thrown, showing more information to the user without having to annotate the full call-stack with `HasCallStack` constraints. A new stack frame value is introduced `AnnFrame`, which consists of nothing but a generic payload. The primop has a small wrapper API that allows users to annotate their call-stack in programs. There is a pure API and an IO-based one. The former is a little bit dubious, as it affects the evaluation of a program, so use with care. The latter is "safe", as it doesn't change the evaluation of the program. The stack annotation mechanism is similarly implemented to the `ExceptionAnnotation` and `Exception`, there is a typeclass to indicate something can be pushed onto the call-stack and all values are wrapped in the existential `SomeStackAnnotation`, which recover the type of the annotation payload. There is currently no builtin way to show the stack annotations when `Backtraces` are displayed (i.e., when showing stack traces to the user), which we will address in a follow-up MR. ------------------------- Metric Increase: ghc_experimental_so ------------------------- We increase the size of the package, so this is not unreasonable. Co-Authored-By:fendor <fendor@posteo.de> Co-Authored-By:
Ben Gamari <bgamari.foss@gmail.com>
We introduce a new primop `annotateStack#` which allows us to push arbitrary data onto the call-stack. This allows us to extract the data later when decoding the stack, for example when an exception is thrown, showing more information to the user without having to annotate the full call-stack with `HasCallStack` constraints. A new stack frame value is introduced `AnnFrame`, which consists of nothing but a generic payload. The primop has a small wrapper API that allows users to annotate their call-stack in programs. There is a pure API and an IO-based one. The former is a little bit dubious, as it affects the evaluation of a program, so use with care. The latter is "safe", as it doesn't change the evaluation of the program. The stack annotation mechanism is similarly implemented to the `ExceptionAnnotation` and `Exception`, there is a typeclass to indicate something can be pushed onto the call-stack and all values are wrapped in the existential `SomeStackAnnotation`, which recover the type of the annotation payload. There is currently no builtin way to show the stack annotations when `Backtraces` are displayed (i.e., when showing stack traces to the user), which we will address in a follow-up MR. ------------------------- Metric Increase: ghc_experimental_so ------------------------- We increase the size of the package, so this is not unreasonable. Co-Authored-By:
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