gnu: Add ghc-concurrent-extra.

* gnu/packages/haskell-xyz.scm (ghc-concurrent-extra): New variable.

gnu/packages/haskell-xyz.scm

@@ -18,11 +18,64 @@
 
 (define-module (gnu packages haskell-xyz)
   #:use-module (gnu packages)
+  #:use-module (gnu packages haskell)
+  #:use-module (gnu packages haskell-check)
   #:use-module (guix build-system haskell)
   #:use-module (guix download)
   #:use-module ((guix licenses) #:prefix license:)
   #:use-module (guix packages))
 
+(define-public ghc-concurrent-extra
+  (package
+    (name "ghc-concurrent-extra")
+    (version "0.7.0.12")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (string-append "https://hackage.haskell.org/package/"
+                           "concurrent-extra/concurrent-extra-"
+                           version ".tar.gz"))
+       (sha256
+        (base32
+         "1y8xk460fvnw0idzdiylmm874sjny4q9jxb1js9fjz8lw2wns3h4"))))
+    (build-system haskell-build-system)
+    (arguments
+     ;; XXX: The ReadWriteLock 'stressTest' fails.
+     `(#:tests? #f))
+    (inputs
+     `(("ghc-unbounded-delays" ,ghc-unbounded-delays)))
+    (native-inputs
+     `(("ghc-async" ,ghc-async)
+       ("ghc-hunit" ,ghc-hunit)
+       ("ghc-random" ,ghc-random)
+       ("ghc-test-framework" ,ghc-test-framework)
+       ("ghc-test-framework-hunit" ,ghc-test-framework-hunit)))
+    (home-page "https://github.com/basvandijk/concurrent-extra")
+    (synopsis "Extra concurrency primitives")
+    (description "This Haskell library offers (among other things) the
+following selection of synchronisation primitives:
+
+@itemize
+@item @code{Broadcast}: Wake multiple threads by broadcasting a value.
+@item @code{Event}: Wake multiple threads by signalling an event.
+@item @code{Lock}: Enforce exclusive access to a resource.  Also known
+as a binary semaphore or mutex.  The package additionally provides an
+alternative that works in the STM monad.
+@item @code{RLock}: A lock which can be acquired multiple times by the
+same thread.  Also known as a reentrant mutex.
+@item @code{ReadWriteLock}: Multiple-reader, single-writer locks.  Used
+to protect shared resources which may be concurrently read, but only
+sequentially written.
+@item @code{ReadWriteVar}: Concurrent read, sequential write variables.
+@end itemize
+
+Please consult the API documentation of the individual modules for more
+detailed information.
+
+This package was inspired by the concurrency libraries of Java and
+Python.")
+    (license license:bsd-3)))
+
 (define-public ghc-language-glsl
   (package
     (name "ghc-language-glsl")