Miranda Language Support for VS Code

A VS Code extension providing rich editing support for the Miranda lazy functional programming language via the Language Server Protocol (LSP).

Features

File extensions

.m and .mir are registered as Miranda source files.

Note: .m is also used by Objective-C. If you work in both languages, VS Code will ask which language to use when you first open a .m file. You can set "files.associations": {"*.m": "miranda"} in your workspace settings.json to prefer Miranda.

Architecture

miranda-lsp/
├── package.json                 Extension manifest (languages, grammars, config)
├── language-configuration.json  Bracket pairs, comment token, word pattern
├── syntaxes/
│   └── miranda.tmLanguage.json  TextMate grammar for syntax highlighting
├── client/
│   └── src/extension.ts         VS Code extension entry point (starts the server)
└── server/
    └── src/server.ts            LSP server (completions, hover, diagnostics, symbols)

How it works

1. VS Code activates the extension for any file whose language ID is miranda.
2. client/src/extension.ts spawns server/out/server.js as a child Node.js process and connects to it over IPC using vscode-languageclient.
3. The server registers its capabilities (completions, hover, diagnostics, document symbols) during the LSP initialize handshake.
4. As you edit a .m file, VS Code sends LSP requests to the server and renders the responses (underlines, completions pop-up, hover tooltips, etc.).

Syntax highlighting

The TextMate grammar (syntaxes/miranda.tmLanguage.json) uses regex rules to colour:

• || … – line comments
• "…" / 'x' – string and character literals
• %include, %export, %insert – preprocessor directives
• ::= / :: / == – type operators
• where, if, then, else, otherwise, abstype, with, div, mod – keywords
• num, bool, char – primitive types
• True, False – boolean literals
• [A-Z]… – constructors / type names
• Arithmetic and relational operators

Language server

The server (server/src/server.ts) is a standalone Node.js process using the vscode-languageserver package. Key subsystems:

Completions (onCompletion / onCompletionResolve)

Returns three layers of items:

1. Keywords – where, if, True, %include, type names, etc.
2. Prelude built-ins – every function in the Miranda standard library, with full type signature as the detail string.
3. User-defined names – scanned from name :: … type signature lines in the current file.

onCompletionResolve fills in the Markdown documentation popup when a built-in item is selected.

Hover (onHover)

1. Identifies the word under the cursor with a simple regex scan.
2. Checks the built-in map first.
3. Falls back to searching the document for a type signature name :: …. If one is found, any || … comment lines immediately above it are shown as the description.

Diagnostics (validateDocument)

Each line is processed by stripLine, which removes comments and string/char literals (preserving column positions). The remaining "logical" content is scanned character-by-character to track bracket balance. Errors are reported for:

• Unexpected ) or ] with no matching opener
• Still-open ( or [ at end of file
• Unclosed " string literals

Document symbols (onDocumentSymbol)

Regex patterns are applied to each non-comment line to detect:

Miranda quick-reference

|| Line comment

|| Type signature
factorial :: num -> num

|| Guarded definition
factorial n = 1,          n = 0
            = n * factorial (n-1), otherwise

|| List comprehension
evens = [ x | x <- [1..20]; x mod 2 = 0 ]

|| Algebraic type
tree * ::= Leaf | Node (tree *) * (tree *)

|| Type synonym
string == [char]

|| Abstract type
abstype stack *
with
    empty  :: stack *
    push   :: * -> stack * -> stack *
    pop    :: stack * -> stack *
    top    :: stack * -> *
    isempty :: stack * -> bool

|| Lambda
double = map (\x . x * 2)

|| Where clause
hypotenuse a b = sqrt (sq a + sq b)
                 where sq x = x * x

|| Include another file
%include "prelude.m"