fix: C backend String functions, record type aliases, docs cleanup

- Add String.fromChar, chars, substring, toUpper, toLower, replace,
  startsWith, endsWith, join to C backend
- Fix record type alias unification by adding expand_type_alias and
  unify_with_env functions
- Update docs to reflect current implementation status
- Clean up outdated roadmap items and fix inconsistencies
- Add comprehensive language comparison document

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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# Lux Language Server Protocol (LSP)
Lux includes a built-in language server that provides IDE features for any editor that supports the Language Server Protocol.
## Quick Start
### Starting the LSP Server
```bash
lux lsp
```
The server communicates via stdio (stdin/stdout), following the standard LSP protocol.
## Supported Features
| Feature | Status | Description |
|---------|--------|-------------|
| Diagnostics | Full | Real-time parse and type errors |
| Hover | Full | Type information and documentation |
| Completions | Full | Context-aware code completion |
| Go to Definition | Full | Jump to function/type definitions |
| Formatting | CLI only | Code formatting via `lux fmt` (not exposed via LSP) |
| Rename | Planned | Rename symbols |
| Find References | Planned | Find all usages |
## Editor Setup
### VS Code
1. Install the Lux extension from the VS Code marketplace (coming soon)
2. Or configure manually in `settings.json`:
```json
{
"lux.lspPath": "/path/to/lux",
"lux.enableLsp": true
}
```
3. Or use a generic LSP client extension like [vscode-languageclient](https://github.com/microsoft/vscode-languageserver-node):
```json
{
"languageServerExample.serverPath": "lux",
"languageServerExample.serverArgs": ["lsp"]
}
```
### Neovim (with nvim-lspconfig)
Add to your Neovim config (`init.lua`):
```lua
local lspconfig = require('lspconfig')
local configs = require('lspconfig.configs')
-- Register Lux as a new LSP
if not configs.lux then
configs.lux = {
default_config = {
cmd = { 'lux', 'lsp' },
filetypes = { 'lux' },
root_dir = function(fname)
return lspconfig.util.find_git_ancestor(fname) or vim.fn.getcwd()
end,
settings = {},
},
}
end
-- Enable the server
lspconfig.lux.setup{}
```
Also add filetype detection in `~/.config/nvim/ftdetect/lux.vim`:
```vim
au BufRead,BufNewFile *.lux set filetype=lux
```
### Neovim (with built-in LSP)
```lua
vim.api.nvim_create_autocmd('FileType', {
pattern = 'lux',
callback = function()
vim.lsp.start({
name = 'lux',
cmd = { 'lux', 'lsp' },
root_dir = vim.fs.dirname(vim.fs.find({ '.git', 'lux.toml' }, { upward = true })[1]),
})
end,
})
```
### Emacs (with lsp-mode)
Add to your Emacs config:
```elisp
(use-package lsp-mode
:hook (lux-mode . lsp)
:config
(add-to-list 'lsp-language-id-configuration '(lux-mode . "lux"))
(lsp-register-client
(make-lsp-client
:new-connection (lsp-stdio-connection '("lux" "lsp"))
:major-modes '(lux-mode)
:server-id 'lux-lsp)))
```
### Emacs (with eglot)
```elisp
(add-to-list 'eglot-server-programs '(lux-mode . ("lux" "lsp")))
```
### Helix
Add to `~/.config/helix/languages.toml`:
```toml
[[language]]
name = "lux"
scope = "source.lux"
injection-regex = "lux"
file-types = ["lux"]
roots = ["lux.toml", ".git"]
comment-token = "//"
indent = { tab-width = 4, unit = " " }
language-server = { command = "lux", args = ["lsp"] }
```
### Sublime Text (with LSP package)
Add to `Preferences > Package Settings > LSP > Settings`:
```json
{
"clients": {
"lux": {
"enabled": true,
"command": ["lux", "lsp"],
"selector": "source.lux"
}
}
}
```
### Zed
Add to your Zed settings:
```json
{
"lsp": {
"lux": {
"binary": {
"path": "lux",
"arguments": ["lsp"]
}
}
}
}
```
## Feature Details
### Diagnostics
The LSP server provides real-time diagnostics for:
- **Parse errors**: Syntax issues, missing tokens, unexpected input
- **Type errors**: Type mismatches, missing fields, unknown identifiers
- **Effect errors**: Missing effect declarations, unhandled effects
- **Behavioral type errors**: Violations of `is pure`, `is total`, etc.
Diagnostics appear as you type, typically within 100ms of changes.
Example diagnostic:
```
error[E0308]: mismatched types
--> src/main.lux:10:5
|
10 | return "hello"
| ^^^^^^^ expected Int, found String
```
### Hover Information
Hover over any symbol to see:
- **Functions**: Signature and documentation
- **Types**: Type definition
- **Keywords**: Syntax explanation
- **Effects**: Effect operations
Example hover for `List.map`:
```markdown
```lux
List.map(list: List<A>, f: A -> B): List<B>
```
Transform each element in a list by applying a function.
```
### Completions
The LSP provides context-aware completions:
#### Module Member Completions
After typing a module name and `.`, you get relevant members:
```lux
List. // Shows: map, filter, fold, reverse, etc.
String. // Shows: length, split, join, trim, etc.
Console. // Shows: print, readLine, readInt
```
#### Keyword Completions
At the start of statements:
```lux
fn // Function declaration
let // Variable binding
type // Type declaration
effect // Effect declaration
match // Pattern matching
```
#### Type Completions
In type position:
```lux
Int, Float, Bool, String, Unit
List, Option, Result
```
### Go to Definition
Jump to the definition of:
- **Functions**: Goes to the `fn` declaration
- **Types**: Goes to the `type` declaration
- **Effects**: Goes to the `effect` declaration
- **Let bindings**: Goes to the `let` statement
- **Imports**: Goes to the imported module
Works with:
- `Ctrl+Click` / `Cmd+Click` in most editors
- `gd` in Vim/Neovim
- `M-.` in Emacs
## Module Completions Reference
### List Module
| Method | Signature | Description |
|--------|-----------|-------------|
| `length` | `(list: List<A>): Int` | Get list length |
| `head` | `(list: List<A>): Option<A>` | First element |
| `tail` | `(list: List<A>): List<A>` | All but first |
| `map` | `(list: List<A>, f: A -> B): List<B>` | Transform elements |
| `filter` | `(list: List<A>, p: A -> Bool): List<A>` | Keep matching |
| `fold` | `(list: List<A>, init: B, f: (B, A) -> B): B` | Reduce |
| `reverse` | `(list: List<A>): List<A>` | Reverse order |
| `concat` | `(a: List<A>, b: List<A>): List<A>` | Join lists |
| `range` | `(start: Int, end: Int): List<Int>` | Create range |
| `get` | `(list: List<A>, index: Int): Option<A>` | Get at index |
| `find` | `(list: List<A>, p: A -> Bool): Option<A>` | Find first match |
| `isEmpty` | `(list: List<A>): Bool` | Check empty |
| `take` | `(list: List<A>, n: Int): List<A>` | Take n elements |
| `drop` | `(list: List<A>, n: Int): List<A>` | Drop n elements |
| `any` | `(list: List<A>, p: A -> Bool): Bool` | Any matches |
| `all` | `(list: List<A>, p: A -> Bool): Bool` | All match |
### String Module
| Method | Signature | Description |
|--------|-----------|-------------|
| `length` | `(s: String): Int` | String length |
| `split` | `(s: String, delim: String): List<String>` | Split by delimiter |
| `join` | `(list: List<String>, delim: String): String` | Join with delimiter |
| `trim` | `(s: String): String` | Remove whitespace |
| `contains` | `(s: String, sub: String): Bool` | Check contains |
| `replace` | `(s: String, from: String, to: String): String` | Replace |
| `chars` | `(s: String): List<String>` | To char list |
| `lines` | `(s: String): List<String>` | Split into lines |
| `toUpper` | `(s: String): String` | Uppercase |
| `toLower` | `(s: String): String` | Lowercase |
### Console Effect
| Operation | Signature | Description |
|-----------|-----------|-------------|
| `print` | `(msg: String): Unit` | Print message |
| `readLine` | `(): String` | Read line |
| `readInt` | `(): Int` | Read integer |
### Math Module
| Function | Signature | Description |
|----------|-----------|-------------|
| `abs` | `(x: Int): Int` | Absolute value |
| `min` | `(a: Int, b: Int): Int` | Minimum |
| `max` | `(a: Int, b: Int): Int` | Maximum |
| `pow` | `(base: Float, exp: Float): Float` | Exponentiation |
| `sqrt` | `(x: Float): Float` | Square root |
| `floor` | `(x: Float): Int` | Floor |
| `ceil` | `(x: Float): Int` | Ceiling |
| `round` | `(x: Float): Int` | Round |
### File Effect
| Operation | Signature | Description |
|-----------|-----------|-------------|
| `read` | `(path: String): String` | Read file |
| `write` | `(path: String, content: String): Unit` | Write file |
| `exists` | `(path: String): Bool` | Check exists |
| `delete` | `(path: String): Bool` | Delete file |
| `listDir` | `(path: String): List<String>` | List directory |
| `mkdir` | `(path: String): Bool` | Create directory |
### Http Effect
| Operation | Signature | Description |
|-----------|-----------|-------------|
| `get` | `(url: String): Result<String, String>` | HTTP GET |
| `post` | `(url: String, body: String): Result<String, String>` | HTTP POST |
| `put` | `(url: String, body: String): Result<String, String>` | HTTP PUT |
| `delete` | `(url: String): Result<String, String>` | HTTP DELETE |
### Random Effect
| Operation | Signature | Description |
|-----------|-----------|-------------|
| `int` | `(min: Int, max: Int): Int` | Random integer |
| `float` | `(): Float` | Random float 0-1 |
| `bool` | `(): Bool` | Random boolean |
### Time Effect
| Operation | Signature | Description |
|-----------|-----------|-------------|
| `now` | `(): Int` | Current timestamp (ms) |
| `sleep` | `(ms: Int): Unit` | Sleep for ms |
### Sql Effect
| Operation | Signature | Description |
|-----------|-----------|-------------|
| `connect` | `(url: String): Connection` | Connect to database |
| `query` | `(conn: Connection, sql: String): List<Row>` | Execute query |
| `execute` | `(conn: Connection, sql: String): Int` | Execute statement |
| `transaction` | `(conn: Connection, f: () -> A): A` | Run in transaction |
## Troubleshooting
### LSP Not Starting
1. Verify Lux is installed: `lux --version`
2. Check the server starts: `lux lsp` (should wait for input)
3. Check editor logs for connection errors
### No Completions
1. Ensure file has `.lux` extension
2. Check file is valid (no parse errors)
3. Verify LSP is connected (check status bar)
### Slow Diagnostics
The LSP re-parses and type-checks on every change. For large files:
1. Consider splitting into modules
2. Check for complex recursive types
3. Report performance issues on GitHub
### Debug Logging
Enable verbose logging:
```bash
LUX_LSP_LOG=debug lux lsp
```
Logs are written to stderr.
## Protocol Details
The Lux LSP server implements LSP version 3.17 with the following capabilities:
```json
{
"capabilities": {
"textDocumentSync": "full",
"hoverProvider": true,
"completionProvider": {
"triggerCharacters": ["."]
},
"definitionProvider": true
}
}
```
### Supported Methods
| Method | Support |
|--------|---------|
| `initialize` | Full |
| `shutdown` | Full |
| `textDocument/didOpen` | Full |
| `textDocument/didChange` | Full |
| `textDocument/didClose` | Full |
| `textDocument/hover` | Full |
| `textDocument/completion` | Full |
| `textDocument/definition` | Full |
| `textDocument/publishDiagnostics` | Full (server-initiated) |
## Contributing
The LSP implementation is in `src/lsp.rs`. To add new features:
1. Add capability to `ServerCapabilities`
2. Implement handler in `handle_request`
3. Add tests in `tests/lsp_tests.rs`
4. Update this documentation
See [CONTRIBUTING.md](./CONTRIBUTING.md) for development setup.