Posts for the month of November 2018

GHC 8.6.2 released

The GHC team is very happy to announce the availability of GHC 8.6.2, a bugfix release to GHC 8.6.1. The source distribution, binary distributions, and documentation for this release are available at

The 8.6 release fixes several regressions present in 8.6.1 including:

  • A long-standing (but previously hard to manifest) bug resulting in undefined behavior for some applications of dataToTag# has been fixed (#15696)
  • An incorrect linker path to libgmp in the Mac OS binary distributions (#15404)
  • A regression rendering Windows installations to read-only directories unusable (#15667)
  • A regression resulting in panics while compiling some record updates of GADTs constructors (#15499)
  • A regression resulting in incorrect type errors when splicing types into constraint contexts has been fixed (#15815)
  • Around a dozen other issues.

See Trac for a full list of issues resolved in this release.

Note that this release ships with one significant but long-standing bug (#14251): Calls to functions taking both Float# and Double# may result in incorrect code generation when compiled using the LLVM code generator. This is not a new issue, it has existed as long as the LLVM code generator has existed; however, changes in code generation in 8.6 made it more likely that user code using only lifted types will trigger it.

Happy compiling!


  • Ben