NESL(ID:1740/nes001)Fine-grained, functional, data-parallel language with nested data structures and nested parallelism. Includes a built-in parallel data type and parallel operations on sequences. Loosely based on ML. Useful for parallel algorithms on sparse matrices and graphs." NESL is a parallel language developed at Carnegie Mellon by the SCandAL project. It integrates various ideas from the theory community (parallel algorithms), the languages community (functional languages) and the system's community (many of the implementation techniques). The most important new ideas behind NESL are Nested data parallelism: this feature offers the benefits of data parallelism, concise code that is easy to understand and debug, while being well suited for irregular algorithms, such as algorithms on trees, graphs or sparse matrices (see the examples above or in our library of algorithms). A language based performance model: this gives a formal way to calculated the work and depth of a program. These measures can be related to running time on parallel machines. The main emphasis in the design of NESL was to make parallel programming easy and portable. Algorithms are typically significantly more concise in NESL than in most other parallel programming languages. Furthermore the code closely resembles high-level pseudocode. Here is a comparison of a parallel quicksort in NESL and MPI (10 lines of code vs. 1700). Of course this comes at the cost of placing more responsibility on the compiler and runtime system for achieving good efficiency. People: Structures: Related languages
References: NESL and Nested Parallelism NESL is a high-level language designed to allow simple and concise descriptions of nested data-parallel programs [8]. It is strongly typed and applicative (sideeffect- free). Sequences are the primitive parallel data type and the language provides a large set of built-in parallel sequence operations. Parallelism is achieved through the ability to apply functions in parallel to each element of a sequence. The application of a function over a sequence is specified using a set-like notation similar to set-formers in SETL [37] and list-comprehensions in Miranda [44] and Haskell [26]. For example, the NESL expression {negate(a): a in [3,-4,-9,5] I a < 4} can be read as ?in parallel, for each a in the sequence [3, -4, -9, 51 such that a is less than 4, negate a?. The expression returns [-3, 4, 9] . The parallelism is applied both to the expression to the left of the colon (:) and to the subselection to the right of the pipe ( I). This parallel subselection can be implemented with packing techniques [5]. NESL also supplies a set of parallel functions that operate on sequences as a whole. Figure 2 lists several of these functions; a full list can be found in the NESL manual [8]. These are similar to operations found in other data-parallel languages. in Proceedings of the ACM SIGPLAN International Conference on Functional Programming, May 1996. view details in [ACM] ACM Computing Surveys (CSUR) 30(2) June 1998 view details Resources
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