ParaSail (programming language)

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ParaSail
Logo for ParaSail Programming Language.jpg
Logo for ParaSail Programming Language
Paradigm compiled, concurrent, imperative, structured, object-oriented
Designed by S. Tucker Taft
Developer AdaCore
First appeared2009;16 years ago (2009)
Stable release
9.3 / 6 June 2021;4 years ago (2021-06-06)
Typing discipline strong, static
Platform x86
OS Linux, macOS, Windows
License GPL v3
Filename extensions .psi, .psl
Website parasail-lang.org
Major implementations
psli, pslc
Influenced by
Modula, Ada, Pascal, ML
Influenced
Nim [1]

Parallel Specification and Implementation Language (ParaSail) is an object-oriented parallel programming language. Its design and ongoing implementation is described in a blog [2] and on its official website. [3]

Contents

ParaSail uses a pointer-free programming model, where objects can grow and shrink, and value semantics are used for assignment. It has no global garbage collected heap. Instead, region-based memory management is used throughout. Types can be recursive, so long as the recursive components are declared optional. There are no global variables, no parameter aliasing, and all subexpressions of an expression can be evaluated in parallel. Assertions, preconditions, postconditions, class invariants, etc., are part of the standard syntax, using a Hoare-like notation. Any possible race conditions are detected at compile time.

Initial design of ParaSail began in September 2009, by S. Tucker Taft.

Both an interpreter using the ParaSail virtual machine, and an LLVM-based ParaSail compiler are available. Work stealing is used for scheduling ParaSail's light-weight threads. The latest version can be downloaded from the ParaSail website. [3]

Description

The syntax of ParaSail is similar to Modula, but with a class-and-interface-based object-oriented programming model more similar to Java or C#.

More recently, the parallel constructs of ParaSail have been adapted to other syntaxes, to produce Java-like, Python-like, and Ada-like parallel languages, dubbed, respectively, Javallel, Parython, and Sparkel (named after the Ada subset SPARK on which it is based). Compilers and interpreters for these languages are included with the ParaSail implementation. [3]

Examples

The following is a Hello world program in ParaSail:

funcHello_World(varIO)isIO.Println("Hello, World");endfuncHello_World;

The following is an interface to a basic map module:

interfaceBMap<Key_TypeisOrdered<>;Element_TypeisAssignable<>>isop"[]"()->BMap;// Create an empty mapfuncInsert(varBMap;Key:Key_Type;Value:Element_Type);funcFind(BMap;Key:Key_Type)->optionalElement_Type;funcDelete(varBMap;Key:Key_Type);funcCount(BMap)->Univ_Integer;endinterfaceBMap;

Here is a possible implementation of this map module, using a binary tree:

classBMapisinterfaceBinary_Node<>is// A simple "concrete" binary node modulevarLeft:optionalBinary_Node;varRight:optionalBinary_Node;constKey:Key_Type;varValue:optionalElement_Type;// null means deletedendinterfaceBinary_Node;varTree:optionalBinary_Node;varCount:=0;exportsop"[]"()->BMapis// Create an empty mapreturn(Tree=>null,Count=>0);endop"[]";funcInsert(varBMap;Key:Key_Type;Value:Element_Type)is// Search for Key, overwrite if found, insert new node if notforM=>BMap.TreeloopifMis nullthen// Not already in the map; add itM:=(Key=>Key,Value=>Value,Left=>null,Right=>null);BMap.Count+=1;elsecaseKey=?M.Keyof[#less]=>continueloopwithM.Left;[#greater]=>continueloopwithM.Right;[#equal]=>// Key is already in the map;// bump count if Value was null;ifM.Valueis nullthenBMap.Count+=1;endif;// in any case overwrite the Value fieldM.Value:=Value;return;endcase;endif;endloop;endfuncInsert;funcFind(BMap;Key:Key_Type)->optionalElement_Typeis// Search for Key, return associated Value if present, or null otherwiseforM=>BMap.TreewhileMnot nullloopcaseKey=?M.Keyof[#less]=>continueloopwithM.Left;[#greater]=>continueloopwithM.Right;[#equal]=>// Found it; return the valuereturnM.Value;endcase;endloop;// Not found in BMapreturnnull;endfuncFind;funcDelete(varBMap;Key:Key_Type)is// Search for Key; delete associated node if foundforM=>BMap.TreewhileMnot nullloopcaseKey=?M.Keyof[#less]=>continueloopwithM.Left;[#greater]=>continueloopwithM.Right;[#equal]=>// Found it; if at most one subtree is non-null, overwrite// it; otherwise, set its value field to null// (to avoid a more complex re-balancing).ifM.Leftis nullthen// Move right subtree into MM<==M.Right;elsifM.Rightis nullthen// Move left subtree into MM<==M.Left;else// Cannot immediately reclaim node;// set value field to null instead.M.Value:=null;endif;// Decrement countBMap.Count-=1;endcase;endloop;// Not found in the mapendfuncDelete;funcCount(BMap)->Univ_Integeris// Return count of number of items in mapreturnBMap.Count;endfuncCount;endclassBMap;

Here is a simple test program for the BMap module:

importPSL::Core::Random;importBMap;funcTest_BMap(Num:Univ_Integer;Seed:Univ_Integer)is// Test the Binary-Tree-based MapvarRan:Random:=Start(Seed);// Start a random-number sequence// Declare a map from integers to stringsvarM:BMap<Key_Type=>Univ_Integer,Element_Type=>Univ_String>;M:=[];// Initialize the map to the empty mapforIin1..Num*2forwardloop// Add elements to the mapconstKey:=Next(Ran)modNum+1;constVal:="Val"|To_String(I);Println("About to insert "|Key|" => "|Val);Insert(M,Key,Val);endloop;Println("Count = "|Count(M));forIin1..Numloop// Search for elements in the mapconstKey:=Next(Ran)modNum+1;Println("Looking for "|Key|", found "|Find(M,Key));endloop;forIin1..Num/3loop// Delete some elements from the mapconstKey:=Next(Ran)modNum+1;Println("About to delete "|Key);Delete(M,Key);endloop;Println("Count = "|Count(M));forIin1..Numforwardloop// Search again for elements in the mapPrintln("Looking for "|I|", found "|Find(M,I));endloop;endfuncTest_BMap;

References

  1. ↑ Rumpf, Andreas (19 October 2017). "Nim without GC". Araq's Musings. Retrieved 1 September 2020.
  2. ↑ ParaSail blog
  3. 1 2 3 ParaSail website

General references


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