Key references in distributed computer systems 1959–1989

Taxonomy, Definition, Approaches, Benefits, Reusability Levels, Factors and Adaption of Software Reusability: A Review of the Research Literature

The design and implementation of a dynamic feature for a high-level language

1. I n t r o d u c t i o n . R concu r ren t a lgor i thm for f ind ing the fewes t number of queens needed to \"cover\" the nxn chessboard, 1.~n~<8, is given here in the Modcap programming language. This algorithm is a straightforward generalization of a good serial algorithm and uses concurrency at two levels: $1MD and MIMD. The Hodcap language is well suited for coding this algorithm since i t contains primitive operations on sets of natural numbers to express the SIHD parallelism and concurrently evaluable f unc t i ons (i.e. tasks ) to express the i'lIHO para l le l ism. The idea of the a lgo r i thm ls f i r s t to f ind a good cover t h a t uses few queens and then prove by exhaust ive search t h a t t h i s cover, or a b e t t e r one discovered dur ing the search, is best possible. SIHD para l le l i sm is involved in the s e t t h e o r e t i c opera t ions t h a t are used to ca lcu la te coverage of the chessboard dur ing both phases of the a lgor i thm. MIMD para l le l i sm is involved p r i m a r i l y dur ing the exhaust ive search phase of the a lgor i thm, mherein var ious d i s jo in t pa r t s of the search are assigned to independent func t ions t h a t may be evaluated concur ren t l y . MIHD para l le l i sm is also used dur ing the p reca l cu la t i on of cover ing sets fo r queens on each of the nxn squres of the board and of c e r t a i n t r a n s f o r m a t i o n indices of squares used to prune redundant branches of the search t ree. R p re l im ina ry re ference manual fo r Modcap appeared in December 1964 [l tRN]. However, to make th i s paper se l f contained, a sho r t appendix about Hodcap is included, as are numerous embedded comments w i t h in the programs ( in t roduced by ¢ symbols).

A concurrent N ≤ 8 Queens' algorithm using modcap

Identifiers are used in programming systems to name assorted quantities such as variables, functions , fields, exceptions, files, and labels . The form of an identifier varies from programming language to programming language and sometimes from use to use within a single language or system . However, there i s increasingly a common intersection among modern languages with respect to identifier syntax . For instance , most languages now require an identifier to begin with a letter, allow mixed letters and digits after that, an d utilize an underscore to emulate a hyphen or space in long identifiers . While satisfactory, there are times when more readable programs would be possible if other characters such as operator symbols, punctuation symbol s or blank spaces were permitted within identifiers . More important than the form of identifiers is their concordant use. In the Modcap programmin g language [We185/87/89], identifiers (apart from twelve reserved words) are used only to name \"variables\" o f the various preand user-defined set-theoretic types . The quotation marks are used here because a variable with a very small (e .g., singleton) type cannot actually vary ; it is effectively a named constant . This consistency has the significant benefit that the user has only one set of name-scope rules to learn. The mos t annoying negative aspect has been the lack of a simple mnemonic field referencing facility for structures . This paper discusses a scheme recently incorporated into Modcap that both mitigates this deficiency and allow s more readable identifiers . The idea is to allow static strings to be used as identifiers . This was feasible because of the existence of advanced features such as first-class multivalued functions and automatic stati c instantiation (in-line code substitution) within the language . It is a natural extension to Modcap's existin g naming facilities that essentially and effectively subsumes the field-referencing notation of Pascal and th e object-oriented notation of Smalltalk . Once discovered, it was fully implemented in less than two days .

Identifiers and static name abstraction

An approach to library organization for block-structured languages is given that avoids corrupting such structuring with the introduction of “modules”, “units”, or “packages”. The scheme involves retentive block structuring and the preservation of partially compiled programs as compiler continuations. Its chief advantage is language simplicity. Its chief disadvantage is, at the present, its proclivity towards redundant file storage. This can possibly be eliminated by adopting a computational model using a one-level store.

Libraries as programs preserved within compiler continuations

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Libraries as programs preserved within compiler continuations

A concurrent N ≤ 8 Queens' algorithm using modcap