Scheme-langserver

You may read my paper and cite like this:

WANG, Z. (2025, May 12). Scheme-langserver: Treat Scheme Code Editing as the First-Class Concern. The 18th European Lisp Symposium (ELS`25), Zurich. https://doi.org/10.5281/zenodo.15384882

Due to occasional GitHub access restrictions from China, this repository is also mirrored on Codeberg and Gitee. I collaborate with XmacsLabs; a fork is available here.

default.mp4

VSCode is now supported! See the setup guide.

Note: Auto-generated type information is available here. It is mainly used for downstream development and debugging.

Implementing IDE features like autocomplete, goto definition, and hover documentation is a significant effort. Compared to languages like Java, Python, JavaScript, or C, language server implementations for Lisp dialects are still scarce. Existing tools such as Geiser, racket langserver, and swish-lint rely primarily on a REPL or keyword tokenization rather than static program analysis.

For example, when editing an incomplete project whose code is not yet fully executable, Geiser can only complete top-level bindings listed by environment-symbols (on Chez Scheme) or raw symbols—not true identifiers. This means local bindings and unfinished code receive no help in recognizing valid identifier scopes. The same limitation applies to goto definition and other core IDE features.

The root cause is that Scheme and other Lisp dialects present a formidable challenge for program analysis: their rich data structures, flexible control flow, and especially macros make static reasoning difficult. But this does not mean Scheme is only for geniuses and meta-programming. With a better editing environment, Scheme can be accessible and productive for everyone.

scheme-langserver is a Language Server Protocol (LSP) implementation for Scheme that provides completion, goto definition, hover, and type inference through static code analysis based on the R6RS standard. It handles incomplete code gracefully and is published via Akku, a Scheme package manager.

The server has been tested on Chez Scheme 9.4, 9.5, and 10.x.

Compilation, Installation & Configuration

See the setup guide.

Workspace Cache

scheme-langserver can persist the analyzed workspace state to a Chez FASL cache so that subsequent restarts skip the expensive init-references phase. Enable it with the --cache-path option:

./run --cache-path ~/.cache/scheme-langserver

The cache file is written to <cache-path>/workspace.fasl. It is saved when the server receives a normal LSP exit or shutdown request; if the process crashes or is killed, the previously saved cache remains usable. The cache is keyed by a manifest that includes the langserver version, Chez version, machine type, and record-layout fingerprint; any mismatch falls back to a cold start. Because Chez FASL is platform-specific, do not share the cache file across machines or Chez versions. When only a few files have changed since the cache was saved, the server performs an incremental refresh and preserves the analysis results for unchanged files.

Typical speedups:

Fixture	Cold startup	Cached startup	Speedup
simple-lib	~31 ms	~1.3 ms	~24x
Synthetic 200-file fixture	~2484 ms	~49 ms	~50x
scheme-langserver itself (128 .sls files)	~55,790 ms	~1750 ms	~32x
scheme-langserver, one file changed	~58,846 ms	~1900 ms	~31x

See doc/analysis/workspace.md §8 and AGENTS.md §11 for implementation details.

Debugging

For troubleshooting tips, see debugging.md.

Recent Status

Active development is focused on bug fixes, performance profiling, and expanding the type inference system. The 2.1.3 release adds a Chez FASL workspace cache that skips the expensive init-references phase on restart. The 2.1.2 release restores bracket-mismatch diagnostics in the fault-tolerant tokenizer. The 2.1.1 release fixes several crashes and diagnostics issues, and adds R7RS/S7 tokenizer compatibility. The 2.1.0 release brings major improvements to diagnostics, macro auto-resolution, and LSP protocol robustness. Planned features include a dedicated VSCode plugin and data-flow analysis.

Release

2.1.3 — Feature release adding a Chez FASL workspace cache with incremental refresh.

What's new in 2.1.3

• Workspace cache: New --cache-path <dir> CLI option persists the analyzed workspace state to a Chez FASL file. On restart, unchanged files skip the expensive init-references phase; changed/added/deleted files are refreshed incrementally. Typical speedups range from ~20x on small fixtures to ~30–50x on larger projects.

Older releases are documented in doc/release-history.md.

What's new in 2.1.2

• Tokenizer:
  • Restore clear diagnostics for unmatched parentheses and brackets (e.g. unclosed parenthesis, unexpected close bracket) during fault-tolerant parsing, while keeping the R7RS/S7 compatibility fixes from 2.1.1.

Features

1. Completion for top-level and local identifier bindings.
2. Goto definition.
3. Compatible with package manager: Akku.
4. File-change synchronization with corresponding index updates.
5. Hover.
6. References and document highlights (document-scoped).
7. Document symbol.
8. Workspace symbol search (workspace/symbol).
9. Catching local identifier bindings in define-syntax, let-syntax, and other macro forms via hand-written rules.
10. Automatic macro resolution (experimental). The generic expander for syntax-rules, syntax-case, let-syntax, and letrec-syntax—plus multi-layer macro cascade propagation—is functionally correct but not enabled in production because it is too slow for real-world projects (it triggers heavy macro expansion and cross-document reference back-propagation for every macro use site). The routing code in analysis/identifier/self-defined-rules/router.sls currently falls back to hand-written rules such as match-process for ufo-match. If you are interested in pushing this research forward—e.g. via lazy expansion, incremental caching, or selective rule generation—contributions and discussions are very welcome!
11. Cross-platform parallel indexing.
12. Custom source-code annotator compatible with .sps files.
13. Peephole optimization for API requests using suspendable tasks.
14. Type inference via a homemade DSL interpreter, now integrated into auto-completion. Parameters whose types match the expected signature are ranked higher, as shown below where length-a and length-b (both integer?) appear first because they match the parameter type required by <=.
15. Supports R6RS, R7RS, and S7 by switching top environments.

send-message
2023 11 21 11 26 41 967266866
{"jsonrpc":"2.0","id":"3","result":[{"label":"length-a"},{"label":"length-b"},{"label":"lambda"},{"label":"latin-1-codec"},{"label":"lcm"},{"label":"least-fixnum"},{"label":"length"},{"label":"let"},{"label":"let*"},{"label":"let*-values"},{"label":"let-syntax"},{"label":"let-values"},{"label":"letrec"},{"label":"letrec*"},{"label":"letrec-syntax"},{"label":"lexical-violation?"},{"label":"list"},{"label":"list->string"},{"label":"list->vector"},{"label":"list-ref"},{"label":"list-sort"},{"label":"list-tail"},{"label":"list?"},{"label":"log"},{"label":"lookahead-char"},{"label":"lookahead-u8"}]}

16. Abstract interpreter that resolves identifiers across multiple file extensions: .scm, .ss, .sps, .sls, .sld.
17. Code diagnostics with LSP-standard source and code fields. Detects library-not-found, duplicate identifiers in binding forms (e.g. (lambda (x x) ...)), unused imports (e.g. (only (rnrs) car) where car is never referenced), and tokenizer syntax errors.

Roadmap

18. Renaming support (textDocument/rename + prepareRename).
19. Formatting (textDocument/formatting).
20. Signature help (textDocument/signatureHelp).
21. Code actions (textDocument/codeAction) — e.g. "Remove unused import", "Organize imports".
22. Full R6RS compatibility.
23. Step-by-step macro expander for self-defined macros.
24. Code evaluation within the language server.
25. Cross-language semantic support via AST transformers.
26. Extract expression/statement into a procedure (refactoring).

Contributing

Pull requests are welcome! Please see AGENTS.md for project conventions, build steps, and coding style before opening a PR.

Vibe Coding with KIMI

Since mid-2025, active development on this project has been assisted by KIMI (Moonshot AI) in a vibe-coding workflow: the maintainer describes intent in natural language, KIMI explores the codebase, proposes changes, and iterates with tests. If you notice commits authored or co-authored by kimi, that is the AI agent trail. Human review and final approval always remain with the maintainer.

Testing

Almost all key procedures and APIs are covered by tests. Run the full suite with:

bash test.sh

For faster feedback during development, run a single test file:

source .akku/bin/activate
scheme --script tests/protocol/apis/test-definition.sps

Note: Tests currently focus on single-threaded execution.

Other Use Cases

Script-Fu in GIMP

Script-Fu is based on Scheme. Using this example, you can apply scheme-langserver to .scm files in GIMP.

Other Potential Targets

Possible future targets include OMN (Opusmodus Notation) and AutoLisp.

Code Count

find . -name "*.sls" ! -path "./.akku/*" |xargs wc -l

Detailed Document

Core Analysis

1. Catching identifier bindings — how the abstract interpreter resolves define, lambda, let, define-record-type, etc.
2. Macro auto-resolution — generic syntax-rules expansion vs hand-written rules
3. Type system & inference — complete type-inference pipeline and DSL
4. Workspace lifecycle — initialization, incremental updates, and refresh batches
5. File dependency graph — topological sorting and linkage matrix

Protocol & Concurrency

6. API request scheduling — request queue, engine time-slicing, cancellation, and document-sync protection
7. Diagnostic publication — how diagnostics are generated, accumulated, and sent

Debugging & Development

8. Debugging guide — enable logs, replay logs, and iterative printf debugging
9. Development guide (中文) / English version
10. AGENTS.md — build steps, testing conventions, coding style, and common traps for contributors

Research & Experiments

11. Scheme-langserver paper (ELS'25) — academic paper on static analysis for Scheme
12. Macro resolution notes — debugging notes for macro identifier capture
13. Syntax candy DSL — pattern matcher for type-rule authoring
14. Record type inference analysis — define-record-type in the type system
15. Type inference benchmark — performance measurement methodology
16. DeepWiki

License

MIT

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Contributors