1.4. GHC version numbering policy
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## 1.4. GHC version numbering policy

As of GHC version 6.8, we have adopted the following policy for numbering GHC versions:

Stable Releases

  Stable branches are numbered ``x`.`y``, where `y` is even. Releases on the stable branch ``x`.`y`` are numbered ``x`.`y`.`z``, where `z` (>= 1) is the patchlevel number. Patchlevels are bug-fix releases only, and never change the programmer interface to any system-supplied code. However, if you install a new patchlevel over an old one you will need to recompile any code that was compiled against the old libraries.

  The value of `__GLASGOW_HASKELL__` (see Section 4.12.3, “Options affecting the C pre-processor”) for a major release ``x`.`y`.`z`` is the integer `xyy` (if `y` is a single digit, then a leading zero is added, so for example in version 6.8.2 of GHC we would have `__GLASGOW_HASKELL__==608`).

Stable snapshots

  We may make snapshot releases of the current stable branch available for download, and the latest sources are available from the git repositories.

  Stable snapshot releases are named ``x`.`y`.`z`.`YYYYMMDD``. where ``YYYYMMDD`` is the date of the sources from which the snapshot was built, and ``x`.`y`.`z+1`` is the next release to be made on that branch. For example, `6.8.1.20040225` would be a snapshot of the `6.8` branch during the development of `6.8.2`.

  The value of `__GLASGOW_HASKELL__` for a snapshot release is the integer `xyy`. You should never write any conditional code which tests for this value, however: since interfaces change on a day-to-day basis, and we don't have finer granularity in the values of `__GLASGOW_HASKELL__`, you should only conditionally compile using predicates which test whether `__GLASGOW_HASKELL__` is equal to, later than, or earlier than a given major release.

Unstable snapshots

  We may make snapshot releases of the HEAD available for download, and the latest sources are available from the git repositories.

  Unstable snapshot releases are named ``x`.`y`.`YYYYMMDD``. where ``YYYYMMDD`` is the date of the sources from which the snapshot was built. For example, `6.7.20040225` would be a snapshot of the HEAD before the creation of the `6.8` branch.

  The value of `__GLASGOW_HASKELL__` for a snapshot release is the integer `xyy`. You should never write any conditional code which tests for this value, however: since interfaces change on a day-to-day basis, and we don't have finer granularity in the values of `__GLASGOW_HASKELL__`, you should only conditionally compile using predicates which test whether `__GLASGOW_HASKELL__` is equal to, later than, or earlier than a given major release.

The version number of your copy of GHC can be found by invoking `ghc` with the `––version` flag (see Section 4.6, “Help and verbosity options”).

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