[Git][ghc/ghc][wip/pmcheck-release-notes-8.12] Release Notes: Add news from the pattern-match checker [skip ci]

[Sebastian Graf]

Sebastian Graf pushed to branch wip/pmcheck-release-notes-8.12 at Glasgow Haskell Compiler / GHC


Commits:
4c7e9689 by Sebastian Graf at 2020-06-11T10:37:38+02:00
Release Notes: Add news from the pattern-match checker [skip ci]

- - - - -


1 changed file:

- docs/users_guide/8.12.1-notes.rst


Changes:

=====================================
docs/users_guide/8.12.1-notes.rst
=====================================
@@ -19,6 +19,19 @@ Highlights
     In the mean this improved runtime by about 0.8%. For details
     see ticket :ghc-ticket:`17823`.
 
+* Pattern-Match Coverage Checking
+
+  - The revamp of the pattern-match coverage checker that started in 8.10 concludes with this release and implements the 
+    novel `*Lower Your Guards* <https://www.microsoft.com/en-us/research/uploads/prod/2020/03/lyg.pdf>`_ algorithm.
+  - Compared to 8.10, end users might notice improvements to "long-distance information": :: haskell
+
+      :linenos:   
+      f True = 1
+      f x    = ... case x of { False -> 2; True -> 3 } ...
+
+    GHC is now able to detect the case alt returning 3 as redundant.
+  - Some more performance improvements in edge cases.
+
 Full details
 ------------
 



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/4c7e9689f6fcc3eb974f0a76ae8078abda30026d

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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/4c7e9689f6fcc3eb974f0a76ae8078abda30026d
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