libraries/base/GHC/Err.hs¶
Note [Errors in base]¶
As of base-4.9.0.0, error produces a stack trace alongside the error message using the HasCallStack machinery. This provides a partial stack trace, containing the call-site of each function with a HasCallStack constraint.
In base, however, the only functions that have such constraints are error and undefined, so the stack traces from partial functions in base will never contain a call-site in user code. Instead we’ll usually just get the actual call to error. Base functions already have a good habit of providing detailed error messages, including the name of the offending partial function, so the partial stack-trace does not provide any extra information, just noise. Thus, we export the callstack-aware error, but within base we use the errorWithoutStackTrace variant for more hygienic error messages.
