Scheme Reports at Fifty

Summary

Based on my talk at the Scheme Workshop 2025. You might prefer to have me talk it at you instead. We are holding an election to the Scheme Steering Committee. Register to vote and nominate candidates! In December this year, the Scheme reports will turn fifty. As chair of the working group entrusted with the next major revision of the report, I want to start a discussion in the Scheme community about what a good Scheme report looks like in 2025, and how it’s different from what it looked like in 1975, and from other times when the Scheme report was revised. Who is the Scheme report for? When making any document, we have to consider who we’re writing for, how they’re going to use it, and what they want and need from it in order to do their thing. For the Scheme report, the obvious two groups are users and implementers. These are very vague groupings, and like any attempt to divide up a group as large and diverse as the Scheme user base, one can’t at all pretend like every member of these groupings has the same views on every issue. Nonetheless, a rule of thumb is that users want their pet features added, creating pressure to grow the report; implementers want to be able to actually create a compiler, creating pressure to keep the report smaller and simpler. But there are also clear subdivisions where even this clear breakdown falls apart, like in the embedded space, where both users and implementers want something that can work on limited-resource environments. Another tension still rarely recognized is between users in education – students learning the language – and long-time Schemers who know it very well. The How to Design Programs approach seems to have worked for many more beginning students than Structure and Interpretation of Computer Programs ever did, because HtDP acknowledges from the start that assuming brand new students will be able to learn with a tool designed for people who are already experts means that tool can’t be as helpful to those just finding ...