Ben Greenman

This paper presents the design of Forge , a tool for teaching formal methods gradually. Forge is based on the widely-used Alloy language and analysis tool, but contains numerous improvements based on more than a decade of experience teaching Alloy to students. Although our focus has been on the classroom, many of the ideas in Forge likely also apply to training in industry. Forge offers a progression of languages that improve the learning experience by only gradually increasing in expressive power. Forge supports custom visualization of its outputs, enabling the use of widely-understood domain-specific representations. Finally, Forge provides a variety of testing features to ease the transition from programming to formal modeling. We present the motivation for and design of these aspects of Forge, and then provide a substantial evaluation based on multiple years of classroom use.

Rhombus is a new language that is built on Racket. It offers the same kind of language extensibility as Racket itself, but using traditional (infix) notation. Although Rhombus is far from the first language to support Lisp-style macros without Lisp-style parentheses, Rhombus offers a novel synthesis of macro technology that is practical and expressive. A key element is the use of multiple binding spaces for context-specific sublanguages. For example, expressions and pattern-matching forms can use the same operators with different meanings and without creating conflicts. Context-sensitive bindings, in turn, facilitate a language design that reduces the notational distance between the core language and macro facilities. For example, repetitions can be defined and used in binding and expression contexts generally, which enables a smoother transition from programming to metaprogramming. Finally, since handling static information (such as types) is also a necessary part of growing macros beyond Lisp, Rhombus includes support in its expansion protocol for communicating static information among bindings and expressions. The Rhombus implementation demonstrates that all of these pieces can work together in a coherent and user-friendly language.