. This paper discusses some of the pros and cons of extending a simple functional language called Sac (for Single Assignment C) by array operations similar to those that are available in Apl. The array operations in Sac are based on the /-calculus, an algebra of arrays which provides a formalism for specifying and simplifying array operations in terms of index set manipulations. The programming techniques made possible by Sac are demonstrated by means of a functional program for the approximation of numerical solutions of partial differential equations by multigrid relaxation. This application is not only of practical relevance but also fully exposes the flavors of using high-level array operations. In contrast to specifications in other languages, e.g. in Fortran or Sisal, the Sac program is well structured, reasonably concise, and - what is most important - invariant against dimensionalities and shapes. However, sophisticated compilation techniques are necessary to avoid, whenever po...

are often successful in easing application development. In this paper, we report our experiences in compiling a recently developed XML Query Language, XQuery for applications that process scientific datasets.

Abstract. Most array operations in Sac are specified in terms of socalled with-loops, a Sac-specific form of array comprehension. Due to the map-like semantics of with-loops its loop instances can be computed in any order which provides considerable freedom when it comes to compiling them into nestings of for-loops in C. This paper discusses several different execution orders and their impact on compilation complexity, size of generated code, and execution runtimes. As a result, a multiply parameterized compilation scheme is proposed which achieves speedups of up to a factor of 16 when compared against a nai"ve compilation scheme. 1 Introduction Sac is a functional C-variant that is particularly aimed at numerical applications involving complex array operations. To allow for a fairly high level of abstraction, Sac supports so-called shape-invariant programming, i.e., all operations/functions can be defined in a way that allows array arguments to have arbitrary extents in an arbitrary number of dimensions. The main language construct for specifying such array operations is the so-called with-loop, a form of array comprehension adjusted to the needs of shape-invariant programming. In [20] it has been shown that the array concept of Sac is suitable for specifying reasonably complex array operations in a shape-invariant style. It has also been shown that such specifications can be compiled into code whose runtimes are competitive with those obtained from rather low-level specifications in other languages such as Sisal or Fortran.

81/2 is a data-parallel language that relies on the notions of stream and collection in a high-level declarative framework. We describe in this research report semantics and compilation of sequential streams of collections for this language. Firstly, a denotational semantics is associated with recursively defined sequential 81/2 streams. Furthermore, we explain how the fixed point calculus corresponding to the foregoing semantics is implemented. Secondly, we describe an effective code generation scheme targetted towards either sequential, vector or SIMD architectures. Then we present four optimization processes for the generated code: the sharing of common control expressions, the optimization of delay copies, the loop fusion and the concatenation optimization. Next, some elements for the evaluation of the generated code are given. As a conclusion, we recall the overall effectiveness of the stream compilation and draw the future work. Key-words: stream, compilation of data-flow graphs...

Recursive definition of streams (infinite lists of values) have been proposed as a fundamental programming structure in various fields. A problem is to turn such expressive recursive definitions into an efficient imperative code for their evaluation. One of the main approach is to restrict the stream expressions to interpret them as a temporal sequence of values. Such sequential stream rely on a clock analysis to decide at what time a new stream value must be produced. In this paper we present a denotational semantics of recursively defined sequential streams. We show how an efficient implementation can be derived as guarded statements wrapped into a single imperative loop.

Abstract. Declarative data parallel programming for shared memory multiprocessor systems implies paradigm-specific demands on the organisation of memory management. As a key feature of declarative programming implicit memory management is indispensable. Yet, the memory objects to be managed are very different from those that are predominant in general-purpose functional or object-oriented languages. Rather than complex structures of relatively small items interconnected by references, we are faced with large chunks of memory, usually arrays, which often account for 100s of MB each. Such sizes make relocation of data or failure to update arrays in-place prohibitively expensive. To address these challenges of the data parallel setting, the functional array language SaC employs continuous garbage collection via reference counting combined with several aggressive optimisation techniques. However, we have observed that overall memory performance does not only rely on efficient reference counting techniques, but to a similar extent on the underlying memory allocation strategy. As in the general memory management setting we can identify specific demands of the declarative data parallel setting on heap organisation. In this paper, we propose a heap manager design tailor-made to the needs of concurrent executions of declarative data parallel programs whose memory management is based on reference counting. We present runtime measurements that quantify the impact of the proposed design and relate it to the performance of several different general purpose heap managers that are available in the public domain. 1