BCPL Language Server

Language Server Protocol support for Martin Richards' BCPL in Visual Studio Code.

This extension is the successor to the original Python-based bcpl-lsp extension. The language server has been reimplemented in C# on .NET 10 and is bundled directly in the extension — no separate server install is needed.

Features

Function references

Inlay hints

Output window log

Diagnostics

Diagnostics are produced by the parser and a small set of semantic checks. Nothing else is reported.

• Error — parser errors (best-effort recovery, so cascading is possible).
• Warning — unresolved symbol references.
• Warning — duplicate GLOBAL slot numbers within a compilation unit.
• Hint — locals and parameters declared but never referenced (skipped when the same name is declared more than once in a file, to avoid false positives).
• Information — "symbol is defined in X; consider adding a GET" when an unresolved reference matches a symbol known to the workspace index.

BCPL Dialect

Targets Martin Richards' canonical BCPL with uppercase keywords (LET, IF, THEN, GET, etc.). The parser has been exercised primarily against the Cintcode and TRIPOS sources; other dialects may expose parser gaps.

Requirements

• .NET 10 runtime. The extension bundles a framework-dependent build of the language server. Install the runtime from https://dotnet.microsoft.com/download/dotnet/10.0. The SDK is not required.

On startup, the extension runs dotnet --list-runtimes and shows an actionable error if a suitable runtime is not found.

Install

Install from the VS Code Marketplace, or download the .vsix from the releases page and run:

code --install-extension bcpl-lsp-<version>.vsix

Upgrading from the Python extension

This extension has the same identifier (se9-solutions.bcpl-lsp) as the earlier Python version, so VS Code treats it as an in-place upgrade. Two things to know:

• The bcpl.server.path setting has changed meaning. It used to point at the Python bcpl-lsp project directory; it now points at a local BCPL-LSP-CSHARP checkout, and is only needed for development. If you had it set, clear it.
• The Python runtime is no longer required. The .NET 10 runtime is, instead.

What this extension does not do

The language server implements only the features listed above. It does not provide:

• Type checking (BCPL is word-oriented and untyped, so there is no type system to check).
• Formatting, code actions, or folding ranges.
• Interpretation of conditional-compilation markers. The /*<TAG ... /*TAG>*/ convention used by some BCPL distributions is treated as a plain block comment; symbols inside an inactive branch will still be indexed.
• Macro expansion beyond MANIFEST constants.
• Precise multi-program disambiguation. When a workspace contains multiple BCPL systems (e.g. Cintcode plus TRIPOS), the server picks the nearest g/ directory by directory proximity. Unusual layouts may need an explicit bcpl.searchPaths setting.
• Incremental re-indexing. Files are parsed in the background after startup; a large directory tree may take a few seconds to fully index on first open.

Bug reports and dialect samples that break the parser are welcome on the repository issue tracker.

Settings

Commands

• BCPL: Language Server Menu — status-bar entry point for the commands below.
• BCPL: Restart Language Server — stops and restarts the server process.
• BCPL: Show Version — displays the current extension version.

File Associations

The extension associates .b and .bcpl files with BCPL. Extensionless files that open as plaintext are sniffed for BCPL constructs (GET, SECTION, LET, GLOBAL, $(, $)) in the first 4 KB and switched to the bcpl language mode if they match.

Using with Claude Code

The bundled language server also works with the Claude Code LSP plugin. Add a .lsp.json file to your project root pointing at the server DLL shipped with this extension (or a separate dotnet publish output):

{
  "bcpl": {
    "command": "dotnet",
    "args": ["/path/to/bcpl-lsp.dll", "--stdio"],
    "extensionToLanguage": { ".b": "bcpl", ".bcpl": "bcpl" },
    "initializationOptions": {
      "searchPaths": ["/path/to/bcpl-81/cintcode/g"]
    }
  }
}

searchPaths tells the server where to find GET headers (e.g. the g/ directory of a Cintcode tree). Without it the server auto-discovers g/ directories inside the workspace.

The .NET 10 runtime is required on whichever host runs the server.

Version History

See CHANGELOG.md for full details.

License

MIT