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.

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 2.1.0 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

2.1.0 — Major release with expanded diagnostics, macro auto-resolution, performance optimizations, and Docker CI upgraded to Chez 10.4.1.

What's new in 2.1.0

• LSP protocol: workspace/symbol search is now supported.
• Diagnostics:
  • Diagnostics now include standard LSP source and code fields.
  • Duplicate identifier detection in binding forms (lambda, case-lambda, let, letrec, let-values, do, define, with-syntax).
  • Unused import detection for only, except, rename, and alias modifiers.
  • Tokenizer syntax errors are now surfaced as document diagnostics.
  • Silent type-inference and type-rule failures are diagnosed.
  • Empty diagnostic arrays are sent to clear stale client-side errors.
• Macro auto-resolution: extended from syntax-rules to syntax-case, let-syntax, and letrec-syntax. Multi-layer macro cascade reference propagation is fixed.
• Type inference: define-record-type now infers record types; car/cdr family macros (caar, cadr, caddr, cadddr, caaar, cadar, etc.) have dedicated type rules.
• Performance: OPT-1~5 optimizations (expander-doc caching, hashtable reverse maps, tail-recursive accumulators, incremental all-pairs maintenance); MEM-1/3/6 memory optimizations for auto macro expansion; dedupe and reference hot-paths switched to eq? hashtables; matrix operations rewritten with cons+reverse.
• Robustness: hardened LSP message parsing against EOF, invalid Content-Length, and malformed JSON; shutdown/exit lifecycle fully compliant with the LSP spec; didChange auto-cancellation removed to comply with the spec; request-queue concurrency hardened with cancel barriers and log-mutex.
• Infrastructure: Docker build chain upgraded from Chez 9.6.4 to 10.4.1; chez-exe switched to the ufo5260987423/chez-exe fork for 10.x compatibility; test suite refactored to use AST search instead of hard-coded positions.

Previous releases

See doc/release-history.md for the full changelog.

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