Building a Scheme Implementation: A Year-Long Journey of Technical Growth and Personal Discovery

In the ever-evolving landscape of programming language implementation, few journeys are as illuminating as the one undertaken by Matthew Plant in his quest to build scheme-rs, a Scheme implementation written in Rust. What began as a modest side project in August 2024 has blossomed into a fully-fledged language runtime that has not only achieved technical milestones but has also profoundly impacted the author's professional trajectory and self-perception as a software engineer.

The genesis of scheme-rs is particularly compelling, emerging not from a calculated business decision or academic requirement, but from a moment of personal uncertainty. Following job loss in August 2024, Plant found himself questioning his place in the software engineering ecosystem. The familiar narrative of professional dissatisfaction had taken hold, and the prospect of finding work that was both challenging and engaging seemed increasingly remote. Rather than pursuing the conventional path of immediate job applications, Plant made a decision that would prove transformative: he would turn inward and rediscover the passion that had originally drawn him to computer science.

This introspective approach led him to dedicate himself fully to scheme-rs, a project that had previously existed in fits and starts without clear direction. The commitment was comprehensive—research, academic rigor, and a determination to implement features correctly rather than expediently. Plant describes purchasing a printer specifically to read academic papers, a tangible manifestation of his dedication to understanding the theoretical foundations underlying his practical work.

From a technical perspective, the evolution of scheme-rs over the past year reveals several fascinating decisions and trade-offs. The most significant architectural shift was the transition from an exclusively asynchronous implementation to one supporting both synchronous and asynchronous execution contexts. This change, while seemingly pragmatic, represents a nuanced understanding of language adoption dynamics. Plant acknowledges that limiting the implementation to async-only would have severely hampered adoption, yet he managed to implement this flexibility without compromising the async capabilities that initially motivated the design. The ability to operate in both contexts demonstrates sophisticated engineering that anticipates diverse use cases.

The current state of scheme-rs, as evidenced by the 0.1.0 release, shows a project that has achieved remarkable stability despite its youth. The completion of 2,258 tests in the R6RS test suite provides concrete validation of the implementation's correctness. However, Plant's transparency about remaining limitations adds credibility to his achievement. The garbage collector, while functional, has substantial room for optimization. Performance, though adequate, represents an area ripe for improvement. The absence of numerous R6RS procedures and the lack of certain features like pattern matching indicate that the implementation, while stable, remains incomplete in terms of feature parity with established Scheme implementations.

Perhaps most intriguing is Plant's vision for the future of scheme-rs. The project serves not merely as an end in itself but as a foundation for a new language that will be built atop it. The consideration of the calculus of constructions for typing suggests ambitions that extend well beyond traditional Scheme implementations. This forward-looking perspective transforms scheme-rs from a language implementation into a platform for language experimentation and innovation.

The personal transformation that accompanied this technical journey cannot be overstated. Plant describes emerging from the year-long project with renewed confidence in his abilities as a software engineer. The PhD, once perceived as the exclusive domain of individuals far more intellectually gifted, now appears within reach. More immediately, the project directly facilitated the discovery of employment that Plant describes as work he "absolutely loves." This outcome illustrates a profound truth about technical work: projects that challenge us deeply often yield benefits far beyond their immediate technical accomplishments.

Plant's recommendation to others with similar cognitive dispositions—to find projects that challenge them as profoundly as scheme-rs challenged him—carries particular weight given his demonstrable success. The advice transcends mere career counseling; it speaks to the fundamental human need for meaningful engagement with difficult problems. In an industry often characterized by rapid iteration and superficial engagement, the deep dive represented by scheme-rs offers a counterpoint that yields both technical mastery and personal growth.

The story of scheme-rs ultimately serves as a case study in the transformative power of committed technical work. It demonstrates how a project born from uncertainty and personal challenge can evolve into a stable, useful tool while simultaneously catalyzing profound personal and professional development. As Plant continues to develop both scheme-rs and the language that will be built upon it, the broader implications of his journey extend beyond the Rust and Scheme communities to anyone seeking meaning and mastery in their technical work.

For those interested in exploring scheme-rs further, the project is available at scheme-rs.org (with DNS propagation expected to complete at scheme.rs) and the source code can be found on GitHub. The project represents not just a technical achievement but a testament to the power of dedicated, challenging work to transform both code and the coder.