VS Code & LSP

Hot provides first-class editor support through a Language Server Protocol (LSP) implementation and VS Code extension.

VS Code Extension

The Hot VS Code extension provides a complete development experience:

• Syntax highlighting — Full Hot language support
• Diagnostics — Real-time error checking and warnings
• Autocomplete — Function, type, and namespace completion
• Hover information — Type info and documentation
• Go to definition — Navigate to function and type definitions

Installation

Install from the VS Code Marketplace:

1. Open VS Code
2. Go to Extensions (Cmd+Shift+X / Ctrl+Shift+X)
3. Search for "Hot" and choose the Hot extension from hot-dev
4. Click Install

Or install from the command line:

code --install-extension hot-dev.hot

Features

Syntax Highlighting

Hot files (.hot) are automatically recognized with full syntax highlighting:

• Declaration keywords (fn, type, enum, ns)
• Control keywords (lazy, do)
• Flow keywords (cond, parallel, serial, match, cond-all, match-all)
• Special syntax (|> pipe, => branch, -> coercion, | union)
• Metadata annotations (meta)
• Strings and template literals
• Numbers and booleans
• Comments
• Namespaces and function paths

Diagnostics

See errors and warnings in real-time as you type:

• Type mismatches
• Undefined functions or variables
• Syntax errors
• Unused variables (warnings)

Errors appear as red squiggles in the editor and in the Problems panel (Cmd+Shift+M).

IntelliSense

Get intelligent code completion as you type:

• Function names with signatures
• Type names and fields
• Namespace paths
• Local variables
• Core library functions

Press Ctrl+Space to trigger autocomplete manually.

Go to Definition

Jump to where a function or type is defined:

• F12 or Cmd+Click — Go to definition
• Cmd+Shift+F12 — Peek definition (inline)
• Shift+F12 — Find all references

Configuration

Configure the extension in VS Code settings:

{
  "hot.lsp.enabled": true,
  "hot.lsp.commandPath": "/usr/local/bin/hot",
  "hot.lsp.extraArgs": []
}

Language Server Protocol

The Hot LSP can be used with any editor that supports LSP.

Starting the LSP Server

hot lsp

The server communicates over stdin/stdout using JSON-RPC.

Neovim Setup

Add to your Neovim configuration:

local lspconfig = require('lspconfig')
local configs = require('lspconfig.configs')

if not configs.hot then
  configs.hot = {
    default_config = {
      cmd = { 'hot', 'lsp' },
      filetypes = { 'hot' },
      root_dir = lspconfig.util.root_pattern('hot.hot', '.git'),
    },
  }
end

lspconfig.hot.setup{}

Emacs Setup

First, define a major mode for .hot files:

(define-derived-mode hot-mode prog-mode "Hot"
  "Major mode for Hot language files.")
(add-to-list 'auto-mode-alist '("\\.hot\\'" . hot-mode))

Then configure lsp-mode:

(use-package lsp-mode
  :hook (hot-mode . lsp)
  :config
  (add-to-list 'lsp-language-id-configuration '(hot-mode . "hot"))
  (lsp-register-client
    (make-lsp-client
      :new-connection (lsp-stdio-connection '("hot" "lsp"))
      :major-modes '(hot-mode)
      :server-id 'hot-lsp)))

Supported Capabilities

Commands

The VS Code extension provides these commands:

REPL Integration

The Hot REPL can be used alongside your editor for interactive development:

hot repl

Features:

• Tab completion
• History (up/down arrows)
• Multi-line input
• Pretty-printed output