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Concurrent Haskell
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<p>Concurrent Haskell (also Control.Concurrent, or Concurrent and Parallel Haskell) is an extension to the <a href="/facts/Functional_programming/cdxqPEIM">functional</a> <a href="/facts/Programming_language/cWTYbgWa">programming language</a> <a href="/facts/Haskell/ydEsHuGy">Haskell</a>, which adds explicit <a href="/facts/Primitive_data_type/0c898228">primitive data types</a> for <a href="/facts/Concurrency_(computer_science)/Ctnrrq4A">concurrency</a>. It was first added to <a href="/facts/Haskell/ydEsHuGy">Haskell 98</a>, and has since become a <a href="/facts/Library_(computing)/xRzL3P7q">library</a> named Control.Concurrent included as part of the <a href="/facts/Glasgow_Haskell_Compiler/4msB3KFN">Glasgow Haskell Compiler</a>. </p><p>Its two main underlying concepts are: </p> <ul><li>A <a href="/facts/Primitive_data_type/0c898228">primitive data type</a> MVar α implementing a bounded/single-place <a href="/facts/Actor_model_and_process_calculi/C29Uux3n">asynchronous channel</a>, which is either empty or holds a value of type α.</li> <li>The ability to spawn a concurrent <a href="/facts/Thread_(computing)/hh8WHyPd">thread</a> via the forkIO primitive.</li></ul> <p>Built on this is a set of useful concurrency and <a href="/facts/Synchronization_(computer_science)/n7ID76uM">synchronizing</a> <a href="/facts/Abstraction_(computer_science)/hAnxmJle">abstractions</a> such as <a href="/facts/Actor_model_and_process_calculi/C29Uux3n">unbounded channels</a>, <a href="/facts/Semaphore_(programming)/BrE1W4Je">semaphores</a> and sample <a href="/facts/Variable_(computer_science)/VoCKtwml">variables</a>. </p><p>Haskell threads have very low overhead: creating, context-switching, and scheduling are all internal to the Haskell <a href="/facts/Runtime_system/YmCuC4xP">runtime system</a>. These Haskell-level threads are mapped onto a configurable number of <a href="/facts/Operating_system/8XTuvMh2">operating system</a> (OS) level threads, usually one per <a href="/facts/Processor_(computing)/z3wPljrI">processor core</a>. </p>