Customization of visualizations in a functional programming environment

CS first-year students expect the user interface of programming environments to be similar to that of common PC applications. A natural evolution of educational programming environments consists in incorporating many of their user-friendly facilities. The authors concentrate in this paper on the facilities that WinHIPE, an environment for functional programming, provides to students for customizing the visualization of expressions. Expressions can be either pretty-printed as text or displayed graphically, showing drawings of lists and binary trees. Besides, fonts, sizes, colors, lines and distances are parameters that can be customized for any visualization. Finally, the visualization of large expressions can be simplified to show only their most relevant parts. Students obtain several benefits from customization facilities. They feel more comfortable with the programming environment WinHIPE, because they can develop more readable programs written "in their personal style". Students can also experiment at small effort with different formats, becoming profident in style issues. Finally customization facilities allow making clear in a course on programming languages the relevant role of visualization in programming tools and their relative independence from language syntax.