Structure-based Editing for the ABC Programming Environment

ABC is an interactive programming language where both ease of learning and ease of use stood high amongst its principle design aims. The language is embedded in a dedicated environment that includes a structure-based editor. To fit in with the design aims, the editor had to be easy to learn, demanding a small command set, and easy to use, demanding a powerful command set and strong support for the user in composing programs, without enforcing a computerscience understanding of issues of syntax and the like. Some novel design rules have led to an interesting editor, where the user may enter and edit text either structurally or non-structurally, without having to use different “modes”. 1991 Mathematics Subject Classification: 68N15, 68Q50. 1991 CR Categories: D19, D.2.2, D.2.6, H.1.2, H.5.2.