| Summary: | The objective of this dissertation was to design and implement a platform-independent, distributed visual programming language / visual programming environment (VPUVPE) called the PictGram system. PictGram (PICTorial proGRAMming) is based on the functional programming paradigm. The PictGram system required the development of three challenging components: (1) a visual lexical specification for graphical tokens, (2) a visual syntactic definition specifying rules by which expressions can be legally combined, and (3) a visual parsing mechanism for graphically represented programs. The construction of PictGram has required an intensive analysis of theories for distributed functional programming languages, and extensive experiments of possible VPUVPE implementation. The theoretical investigation developed a formalism of functional programming language in three design phases: (1) a lexical representation of a visual primitive, (2) visually-expressed syntactic rules for the lexical representation, and (3) semantic interpretation of the visual expression. The practical experiments have integrated such formalisms into two realistic implementation components: (1) a front-end of PictGram manages a construction of the visual expression and (2) a back-end of PictGram, a distributed interpreter, evaluates the visual expression. PictGram was constructed by integrating three sub-goals: (1) to develop a theory of PictGram VPUVPE, (2) to design and implement the PictGram VPUVPE, and (3) to integrate PictGram VPUVPE with distributed interpreters. Pic/Gram allows the users to construct a graphically-represented source program. Pic/Gram translates such a graphical expression into textual expression, then uses an interpreter to evaluate the expression. The result is then translated back to an appropriate graphical form. All programming activities are supported interactively through the system's graphical user interface. This dissertation has investigated visual programming methodologies based on a functional programming paradigm, and a visual programming system, PictGram, has been suggested. A lexeme is expressed by the graphical user components, and a syntactic relationship is specified by the click-and-drop operation. The semantics of the graphically-represented source programs are interpreted by the distributed interpreters. PictGram provides a simple interface that supports a general programming language paradigm.
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