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.. _release-9-2-1:
Version 9.2.1
==============
Language
~~~~~~~~
* :extension:`ImpredicativeTypes`: Finally, polymorphic types have become first class!
GHC 9.2 includes a full implementation of the Quick Look approach to type inference for
impredicative types, as described in in the paper
`A quick look at impredicativity
<https://www.microsoft.com/en-us/research/publication/a-quick-look-at-impredicativity/>`__
(Serrano et al, ICFP 2020). More information here: :ref:`impredicative-polymorphism`.
This replaces the old (undefined, flaky) behaviour of the :extension:`ImpredicativeTypes` extension.
Compiler
~~~~~~~~
- New '-Wredundant-bang-patterns' flag that enables checks for "dead" bangs.
For instance, given this program: ::
f :: Bool -> Bool
f True = False
f !x = x
GHC would report that the bang on ``x`` is redundant and can be removed
since the argument was already forced in the first equation. For more
details see :ghc-flag:`-Wredundant-bang-patterns`
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