Civet

The modern way to write TypeScript.

• Documentation
• Online Civet Playground
• Civet VSCode Extension
• Discord Server
• Plugins for Vite, esbuild, ESM module resolution
• Starter templates for Solid and Solid Start

Quickstart Guide

# Install
npm install -g @danielx/civet
# Run Civet code directly in a REPL
civet
# Transpile typed Civet code into TypeScript in a REPL
civet -c
# Compile Civet source file to TypeScript
civet < source.civet > output.ts
# Execute a simple .civet script (no imports)
civet source.civet ...args...
# Execute a .civet source file in node using ts-node
node --loader ts-node/esm --loader @danielx/civet/esm source.civet

Code Sample

ts, {CompilerOptions} from typescript

DefaultCompilerOptions : CompilerOptions :=
  allowNonTsExtensions: true
  allowJs: true
  target: ts.ScriptTarget.Latest
  moduleResolution: ts.ModuleResolutionKind.NodeJs
  module: ts.ModuleKind.CommonJS
  allowSyntheticDefaultImports: true
  experimentalDecorators: true

fileCache : Record<string, any> := {}

createCompilerHost := (options: CompilerOptions, moduleSearchLocations : string[]) ->
  fileExists := (fileName: string) : boolean ->
    fileCache[fileName]?

  readFile := (fileName: string) ->
    fileCache[fileName]

Things Kept from CoffeeScript

• is → ===
• or, or= → ||, ||=
• and, and= → &&, &&=
• a %% b → (a % b + b) % b
• loop → while(true)
• unless exp → if(!exp)
• until condition → while(!condition)
• Object literal syntax

  x =
    a: 1
    b: 2
    c:
      x: "pretty"
      y: "cool"

• Optional semi-colons
• Indentation based block syntax
• OptionalChain shorthand for index and function application: a?[b] → a?.[b], a?(b) → a?.(b)
• ?= null-coalescing assignment shorthand
• @ this shorthand: @ → this, @id → this.id, {@id} → {id: this.id}
• Prototype shorthand: X:: → X.prototype, X::a → X.prototype.a
• Class static shorthand @
• Chained comparisons: a < b < c → a < b && b < c
• Postfix if/unless/while/until/for
• Block Strings """ / '''
  • #{exp} interpolation in """ strings
• when inside switch automatically breaks
• Multiple , separated case/when expressions
• else → default in switch
• Range literals [0...10], [a..b], [x - 2 .. x + 2]
• Array slices list[0...2] → list.slice(0, 2)
• Slice assignment numbers[3..6] = [-3, -4, -5, -6] → numbers.splice(3, 4, ...[-3, -4, -5, -6])
• Implicit returns
• Late assignment x + y = z → x + (y = z)
• Braceless inline objects x = coolStory: true
• Simplified number method calls 1.toFixed() → 1..toFixed()
• if/switch/for/loop/while/throw expressions
• Destructuring object assignment doesn't require being wrapped in parens at the statement level {a, b} = c → ({a, b} = c)
• Prefix or postfix rest/splats [...a], x = [a...]
• RestProperty in any position {a, ...b, c} = d → {a, c, ...b} = d
• RestElement/RestParameter in any position (first, ...midle, last) -> → function(first, ...middle) { let [last] = middle.splice(-1)}
• /// Heregexp
  • With some changes.
• JSX

Things Removed from CoffeeScript

Most of these can be enabled by adding a "civet coffeeCompat" directive prologue to the top of your file. The goal is to provide a very high level of compatibility with existing CoffeeScript code while offering a fine grained migration path to modern Civet.

• Implicit var declarations (use "civet coffeeCompat" or "civet autoVar")
• on/yes/off/no (use true/false, "civet coffeeCompat", or "civet coffeeBooleans" to add them back)
• not (use !, "civet coffeeCompat", or "civet coffeeNot")
  • not instanceof (use !(a instanceof b), "civet coffeeCompat", or "civet coffeeNot")
  • not of use ("civet coffeeCompat", or "civet coffeeNot")
  • NOTE: CoffeeScript not precedence is dubious. not a < b should be equivalent to !(a < b) but it is in fact !a < b
• do keyword (replaced with JS do, invoke using existing (-> ...)() syntax, "civet coffeeCompat", or "civet coffeeDo")
• for from (use JS for of, "civet coffeeCompat", or "civet coffeeForLoops")
• for own of (use JS for in and check manually, switch to Map#keys/values/entries, or use Object.create(null), or "civet coffeeCompat", or "civet coffeeForLoops")
• for ... when <condition> (use continue if exp inside loop, "civet coffeeCompat", or "civet coffeeForLoops")
• a ? b (use a ?? b, though it doesn't check for undeclared variables; "civet coffeeCompat", or "civet coffeeBinaryExistential" enables a ? b at the cost of losing JS ternary operator)
• a of b (use a in b as in JS, or "civet coffeeCompat", or "civet coffeeOf")
• Backtick embedded JS (replaced by template literals)
• Will add later
  • Conditional assignment a?[x] = 3 → a ? a[x] = 3 : undefined
  • Multiple slice assignment otherNumbers[0...] = numbers[3..6] = [-3, -4, -5, -6]

Things Changed from CoffeeScript

• == → == rather than === (unless you specify "civet coffeeCompat" or "civet coffeeEq")
• != → != rather than !== (unless you specify "civet coffeeCompat" or "civet coffeeEq")
• is not → !== (unless you specify "civet coffeeCompat" or "civet coffeeNot"), instead of isnt (unless you specify "civet coffeeCompat" or "civet coffeeIsnt")
• for in and for of are no longer swapped and become their JS equivalents (unless you specify "civet coffeeCompat" or "civet CoffeeOf")
• a is in b → b.indexOf(a) >= 0 and a is not in b → b.indexOf(a) < 0 instead of a in b and a not in b; a in b remains a in b as in JS, and a not in b → !(a in b) (unless you specify "civet coffeeCompat" or "civet coffeeOf")
• x?.y now compiles to x?.y rather than the if typeof x !== 'undefined' && x !== null if check
• Existential x? → (x != null) no longer checks for undeclared variables.
• x?() → x?.() instead of if (typeof x === 'function') { x() }
• Functions don't implicitly return the last value if there's a semicolon at the end: -> x returns x but -> x; does not
• Backtick embedded JS has been replaced with JS template literals.
• No longer allowing multiple postfix if/unless on the same line (use && or and to combine conditions).
• #{} interpolation in "" strings only when "civet coffeeCompat" or "civet coffeeInterpolation"
• Expanded chained comparisons to work on more operators a in b instanceof C → a in b && b instanceof C
• Postfix iteration/conditionals always wrap the statement #5431: try x() if y → if (y) try x()
• Civet tries to keep the transpiled output verbatim as much as possible. In Coffee (x) → x; but in Civet (x) → (x). Spacing and comments are also preserved as much as possible.
• Heregex / re.X
  • Stay closer to the Python spec
  • Allows both kinds of substitutions #{..}, ${..}.
  • Also allows both kinds of single line comments //, #.
  • Keeps non-newline whitespace inside of character classes.
  • Doesn't require escaping # after space inside of character classes.
  • # is always the start of a comment outside of character classes regardless of leading space (CoffeeScript treats \s+# as comment starts inside and outside of character classes).
  • Might later add a compat flag to get more CoffeeScript compatibility.
  • Might also later add a compat flag to only use ES interpolations and comments inside Heregexes.

Things Added that CoffeeScript didn't

• TypeScript Compatibility
  • Auto-rewrite .[mc]ts → .[mc]js in imports (workaround for: microsoft/TypeScript#37582)
  • Function annotations
  • namespace
  • interface
  • TypeParameters
  • ! non-null assertions
  • := readonly class field initializer

      class A
        x := 3

      class A {
        readonly x = 3
      }

• JS Compatibility
  • var, let, const
  • JS Comment Syntax // and /* */
  • function keyword
  • Braced Blocks (as an alternative to indentation)
  • f?.(x) function application and a?.[x] index OptionalChain longhand
  • a ? b : c ConditionalExpression
  • case statement
  • do, do { ... } until condition
  • Method definitions foo(args) ... in objects/classes
  • get/set method definitions
  • Private identifiers #id
• Convenience for ES6+ Features
  • Const assignment shorthand: a := b → const a = b, {a, b} := c → const {a, b} = c
  • Let assignment shorthand (experimental): a .= b or a ::= b → let a = b
  • Typed versions of above: a: number .= 5 → let a: number = 5 (but note that a: number = 5 is the object literal {a: (number = 5)}).
  • @#id → this.#id shorthand for private identifiers
  • import shorthand: x from ./x → import x from "./x"
  • Dynamic import shorthand: import './x' not at top level (e.g. await import './x' or inside a function) → import('./x')
  • export shorthand: export x, y → export {x, y}
  • Triple backtick Template Strings remove leading indentation for clarity
  • Class constructor shorthand @( ... )
  • ClassStaticBlock @ { ... }
  • < as extends shorthand
• Short function block syntax like Ruby symbol to proc, Crystal, Elm record access
  • Access: x.map &.name → x.map(a => a.name)
  • Nested access + slices: x.map &.profile?.name[0...3] → x.map(a => a.profile?.name.slice(0, 3))
  • Function call: x.map &.callback a, b → x.map($ => $.callback(a, b))
  • Unary operators: x.map !!& → x.map($ => !!$)
  • Binary operators: x.map &+1 → x.map($ => $+1)
• Pipe operator (based on F# pipes, Hack pipes and the TC39 proposal)
  • data |> Object.keys |> console.log equivalent to console.log(Object.keys(data))
  • Use single-argument arrow functions or & shorthand to specify how to use left-hand side
  • |> await, |> yield, and |> return (at end) for wrapping left-hand side with that operation
• Flagging shorthand based on from LiveScript: {+debug, -live, !verbose} → {debug: true, live: false, verbose: false}
• JSX enhancements (inspired by solid-dsl discussions):
  • Indentation: instead of explicitly closing <tag>s or <>s, you can indent the children and Civet will close your tags for you
  • Multiple adjacent elements and/or fragments get automatically combined into a fragment.
  • Arrow function children do not need to be wrapped in braces (assuming they are not preceded by text); this is unambiguous because > isn't valid JSX text. For example, <For> (item) => ... (where function body can be indented).
  • #foo shorthand for id="foo"; also #"foo bar", #`foo ${bar}`, #{expr}
  • .foo shorthand for class="foo" (but must be at least one space after tag name); also .foo.bar, ."foo bar", .`foo ${bar}`, .{expr}
    • "civet react" flag uses className instead of class
  • +foo shorthand for foo={true}, -foo/!foo shorthand for foo={false}
  • Any braced object literal can be used as an attribute: {foo} → foo={foo}, {foo: bar} → foo={bar}, {...foo} remains as is; methods and getters/setters work too.
  • Attribute ...foo shorthand for {...foo}
  • Attribute values without whitespace or suitably wrapped (parenthesized expressions, strings and template strings, regular expressions, array literals, braced object literals) do not need braces: foo=bar → foo={bar}, count=count() → count={count()}, sum=x+1 → sum={x+1}, list=[1, 2, 3] → list={[1, 2, 3]}
  • Attributes can use computed property names: [expr]={value} → {...{[expr]: value}}
  • "civet solid" flag adds correct types for JSX elements and fragments. Use "civet solid client" (default) for client-only code, "civet solid server" for server-only code (SSR only), or "civet solid client server" for isomorphic code that runs on client and server (SSR + hydration).
  • XML comments: <!-- ... --> → {/* ... */}
• CoffeeScript improvements
  • Postfix loop run() loop → while(true) run()
  • Character range literals ["a".."z"], ['f'..'a'], ['0'..'9']
• Shebang line is kept unmodified in output

  #!./node_modules/.bin/ts-node
  console.log "hi"
  

Things Changed from ES6

• Implicit returns, even for multi-statement functions (avoid by specifying a void return type, adding a trailing ; or explicit return, or via the directive "civet -implicitReturns")
• Disallow no parens on single argument arrow function. x => ... must become (x) => ... The reasoning is x -> ... => x(function() ...) in CoffeeScript and having -> and => behave more differently than they already do is bad. Passing an anonymous function to an application without parens is also convenient.
• for(i of x) ... defaults to const declaration → for(const i of x) ...
• Disallow comma operator in conditionals and many other places. if x, y is not allowed. But for i = 0, l = a.length; i < l; i++, i *= 2 is allowed.
• Comma operator in case/when instead becomes multiple conditions.
• Numbers can't end with a dot (otherwise would be ambiguous with CoffeeScript slices y[0..x]). This also implies that you can't access properties of numbers with 1..toString() use 1.toString() instead. When exponent follows a dot it is treated as a property access since an exponent could be a valid property 1.e10 → 1..e10. The workaround is to add a trailing zero 1.0e10 or remove the dot before the exponent 1e10.
• Additional reserved words and, or, loop, until, unless
• Experimental decorator syntax is @@ instead of @ because @ is premium real estate and @id → this.id, and @ is also static fields/methods, etc.

  @@classDecorator
  class X
    @@methodDecorator
    method() {}
  

• when inside switch automatically breaks and adds block scope.
• else inside switch adds block scope.
• No whitespace between unary operators and operands. Mandatory whitespace between condition and ternary ? ex. x ? a : b since x? is the unary existential operator.
• No labels (yet...)

CoffeeScript Compatibility

Civet provides a compatibility prologue directive that aims to be 97+% compatible with existing CoffeeScript2 code (still a work in progress).

Configuration	What it enables
autoVar	declare implicit vars based on assignment to undeclared identifiers
coffeeBooleans	yes, no, on, off
coffeeComment	# single line comments
coffeeDo	do ->, disables ES6 do/while
coffeeEq	== → ===, != → !==
coffeeForLoops	for in, of, from loops behave like they do in CoffeeScript
coffeeInterpolation	"a string with #{myVar}"
coffeeIsnt	isnt → !==
coffeeNot	not → !, a not instanceof b → !(a instanceof b), a not of b → !(a in b)
coffeeOf	a of b → a in b, a in b → b.indexOf(a) >= 0, a not in b → b.indexOf(a) < 0

You can use these with "civet coffeeCompat" to opt in to all or use them bit by bit with "civet coffeeComment coffeeEq coffeeInterpolation". Another possibility is to slowly remove them to provide a way to migrate files a little at a time "civet coffeeCompat -coffeeBooleans -coffeeComment -coffeeEq". Both camel case and hyphens work when specifying options "civet coffee-compat". More options will be added over time until 97+% compatibility is achieved.

ECMAScript Compatibility

You can also specify "civet" prologue directives to increase compatibility with ECMAScript/TypeScript:

Configuration	What it enables
-implicit-returns	turn off implicit return of last value in functions

Other Options

The "civet" prologue directive can also specify the following options:

Configuration	What it enables
tab=NNN	treat tab like NNN spaces (default=1)

For example, "civet tab=2" or "civet tab=4" lets you mix tabs and spaces in a file and be treated like they'd render in VSCode with editor.tabSize set accordingly.

Using Civet in your Node.js Environment

You have now been convinced that Civet is right for your current/next project. Here is how to set up your environment to get productive right away and have a Good Time℠.

Testing

Code coverage with c8 "just works" thanks to their source map integration and Civet's source maps.

Currently Civet's ESM loader depends on ts-node

c8 + Mocha

package.json

  "scripts": {
    "test": "c8 mocha",
    ...
  },
  "c8": {
    "extension": [
      ".civet"
    ]
  },
  "mocha": {
    "extension": [
      "civet"
    ],
    "loader": [
      "ts-node/esm",
      "@danielx/civet/esm.mjs"
    ],
    ...
  ...

ts-node must be configured with transpileOnly (it can't resolve alternative extensions). Also I think module needs to be at least ES2020 for the Civet ESM loader to work.

tsconfig.json

  ...
  "ts-node": {
    "transpileOnly": true,
    "compilerOptions": {
      "module": "ES2020"
    }
  }

If you don't care for code coverage you can skip c8 (but it is so easy why not keep it?).

You can also add .js and .ts extensions if you want to mix and match! Even .coffee will work if you require coffeescript/register or add a loader for it.

Execute the tests

yarn test

Step 4: Enjoy!

Developing

Use the alpha version of Civet Language Server

The language server provides syntax highlighting, completions, hover documentation, symbols outline, red squigglies, and go to definition.

---

Q? Why can't I just use the built-in VSCode TypeScript LSP?

A: VSCode's built in TypeScript LSP can't resolve non .ts/.js, not even with plugins. Maybe one day they'll allow for plugins that let you adjust the resolver and insert a transpilation step but until then a separate language server is necessary.

---

Q? Sometimes the file outline disappears and the red squigglies are all in the wrong place and maybe a notification pops up about some kind of LSP error.

A: I'm sorry that happened to you but the Civet Language Server is still alpha and improving rapidly. Please let me know exactly what happened and I'll try to do better next time.

It may happen when there is a syntax error in your Civet file. You can check and see if it compiles using the CLI tool in the meantime.

Please do submit bug reports / feature requests.

Building

I strongly recommend using esbuild for building / packaging your Civet project.

import esbuild from 'esbuild'
import civetPlugin from '@danielx/civet/esbuild-plugin'

esbuild.build({
  ...,
  plugins: [
    civetPlugin
  ]
}).catch(() => process.exit(1))

It's super fast and works great!

Philosophy

Civet is a large language that feels small. Civet is large because it is mostly a superset of TypeScript, an already large language. Civet feels small because of the coherent design aesthetic: related features look and behave similarly, so when seeing a new feature you can have a good idea what it does, and your existing knowledge of JavaScript and other languages leads you in the right direction.

Civet works with existing tools. We're not trying to replace the TypeScript type checker; we want to amplify its power. We're not trying to change ES semantics; we want to present them in a coherent and expressive way.

Less syntax is preferred.

Context matters. The same tokens can mean different things in different contexts. This shouldn't be arbitrary but based on pragmatic concerns. Things should be consistent where possible, especially conceptually.

Civet builds on top of history. We've taken inspiration from languages like CoffeeScript, Elm, LiveScript, Flow, Haskell, Perl, Python, Ruby, Crystal, Bash, and others.

Civet is pragmatic. Civet design is informed by 25+ years of JavaScript development. Frontend frameworks have come and gone but they all addressed issues that were important for their time. We focus heavily on addressing concerns that real developers feel every day. A key criteria for evaluating features is "how does it work in practice?".

Civet evolves. As the official JS and TS specifications evolve into the future, Civet also evolves favoring compatibility. This may lead us to difficult choices where the future spec has evolved differently than we anticipated (pipe operators, do expressions, pattern matching). In those cases, Civet will adapt to match the latest spec while providing configuration options to allow migration bit by bit while keeping existing code working.

Civet is configurable. There is no single "right way" for everyone at all times. Some of us have older CoffeeScript codebases that would benefit from added types. Others have massive TypeScript applications that could benefit from new language features and shorthand syntax. Civet provides a way to get the benefits bit by bit without a complete rewrite. This same configurability lets us experiment with language features to gain experience and improve them before locking them in. It also allows us to adapt to a changing future.