Editor Support

Kaappi includes a Language Server Protocol (LSP) server for IDE integration.

VS Code

Install the Kaappi Scheme extension:

From source

git clone https://github.com/kaappi/vscode-kaappi
cd vscode-kaappi
npm install
npm run compile

Then press F5 in VS Code to launch an Extension Development Host, or copy the folder to ~/.vscode/extensions/.

Features

• Syntax highlighting for .scm, .sld, .ss, .sls files
• Auto-completion of all 600+ built-in procedures and your definitions
• Hover information showing type and arity of procedures
• Go to Definition — jump to where a symbol is defined (Ctrl+Click or F12)
• Find References — find all uses of a symbol (Shift+F12)
• Document outline — lists all define, define-syntax, define-record-type forms (breadcrumbs and outline view)
• Real-time diagnostics for parse and compile errors
• Bracket matching and auto-closing for parentheses
• Comment toggling — line (;) and block (#| |#)

Configuration

Setting	Default	Description
kaappi.lspPath	kaappi-lsp	Path to the kaappi-lsp binary

If kaappi-lsp is not in your PATH:

{
  "kaappi.lspPath": "/usr/local/bin/kaappi-lsp"
}

Language Server (kaappi-lsp)

The kaappi-lsp binary is included with Kaappi and built alongside the main interpreter. It communicates via JSON-RPC over stdin/stdout following the Language Server Protocol.

Capabilities

Feature	Description
Diagnostics	Parse and compile errors on every file change
Completion	All global symbols, filtered by prefix at cursor
Hover	Type name and arity for any symbol
Go to Definition	Jump to define, define-syntax, or define-record-type for a symbol
Find References	Find all occurrences of a symbol in the document
Document Symbols	Outline of all top-level definitions
Document sync	Full text synchronization

Using with other editors

Any editor with LSP support can use kaappi-lsp. Configure it as a stdio language server for .scm files:

Neovim (nvim-lspconfig):

vim.api.nvim_create_autocmd("FileType", {
  pattern = "scheme",
  callback = function()
    vim.lsp.start({
      name = "kaappi-lsp",
      cmd = { "kaappi-lsp" },
    })
  end,
})

Emacs (eglot):

(add-to-list 'eglot-server-programs '(scheme-mode . ("kaappi-lsp")))

Helix (languages.toml):

[[language]]
name = "scheme"
language-servers = ["kaappi-lsp"]

[language-server.kaappi-lsp]
command = "kaappi-lsp"

Formatting

kaappi fmt canonically formats Scheme source: 2-space R7RS indentation, 80-column reflow, comments preserved. Every write is guarded by a reader round-trip check — the formatted output must read back equal? to the original — so it can never change a program's meaning:

kaappi fmt src/           # format files in place
kaappi fmt --check src/   # list files needing formatting, exit 1 (for CI)

With no file arguments, kaappi fmt reads stdin and writes formatted source to stdout — the shape editor filter commands expect:

• Vim / Neovim — :%!kaappi fmt filters the buffer; wire it to a BufWritePre autocmd for format-on-save.
• Emacs — C-u M-| (shell-command-on-region with replacement) running kaappi fmt.
• Helix — add a formatter to the languages.toml entry above:

[[language]]
name = "scheme"
language-servers = ["kaappi-lsp"]
formatter = { command = "kaappi", args = ["fmt"] }
auto-format = true

• VS Code — use a run-on-save extension to run kaappi fmt ${file} after saving.

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