John A. Gerth

APL two by two-syntax analysis by pairwise reduction

Benkard explains the precedence rules of APL with a syntactic binding hierarchy [1,2]. This paper uses the hierarchy as a basis for developing a more formal description of APL syntax which can be applied directly in a syntax analyzer. The flexibility of this approach makes it useful as a basis for examining the effect of proposed syntax changes and the consequences of previous design choices.

Visual cues for data mining

This paper describes a set of visual techniques, based on principles of human perception and cognition, which can help users analyze and develop intuitions about tabular data. Collections of tabular data are widely available, including, for example, multivariate time series data, customer satisfaction data, stock market performance data, multivariate profiles of companies and individuals, and scientific measurements. In our approach, we show how visual cues can help users perform a number of data mining tasks, including identifying correlations and interaction effects, finding clusters and understanding the semantics of cluster membership, identifying anomalies and outliers, and discovering multivariate relationships among variables. These cues are derived from psychological studies on perceptual organization, visual search, perceptual scaling, and color perception. These visual techniques are presented as a complement to the statistical and algorithmic methods more commonly associated with these tasks, and provide an interactive interface for the human analyst.

Toward shared variable events implications of (@@@@)SVE in APL2

APL2 has two extensions for shared variables, a system function, (@@@@)SVS, which returns the access state of variables and a system variable, (@@@@)SVE, which provides a rudimentary mechanism for detecting events associated with shared variables. Implementation of these constructs raises questions about the signalling rules followed by Shared Variable Processors. This paper discusses those questions and suggests that further research be done.

Indexing and merging in APL

Mathematically, an array may be usefully viewed as a function, in this particular case, as a function of its indices. A proposal is made for an operator which derives such a function for its array operand. The proposal is discussed in the context of a review of indexing constructs in various APL systems.

Design of APL (tutorial)

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