Civet

A Programming Language for the New Millenium

Code More with Less in a TypeScript Superset

Civet playground

Civet is a programming language that compiles to TypeScript or JavaScript, so you can use existing tooling (including VSCode type checking, hints, completion, etc.) while enabling concise and powerful syntax. It starts with 99% JS/TS compatibility, making it easy to transition existing code bases. Then it adds many features and syntactic sugar, with some highlights below and more comprehensive examples in the reference. See also Civet's design philosophy and changelog.

Highlights: Beyond TC39

Civet code on the lefttop, compiled TypeScript output on the rightbottom.

Pattern Matching

TC39 Proposal: Pattern Matching

switch x
  0
    console.log("zero")
  /^\s+$/
    console.log("whitespace")
  [{type: "text", content}, ...rest]
    console.log("leading text", content)

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if (x === 0) {
  console.log("zero");
} else if (
  typeof x === "string" &&
  /^\s+$/.test(x)
) {
  console.log("whitespace");
} else if (
  Array.isArray(x) &&
  x.length >= 1 &&
  typeof x[0] === "object" &&
  x[0] != null &&
  "type" in x[0] &&
  x[0].type === "text" &&
  "content" in x[0]
) {
  const [{ type, content }, ...rest] = x;
  console.log("leading text", content);
}

Ligatures

Pipelines

TC39 Proposal: Pipe Operator

data
  |> Object.keys
  |> console.log

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console.log(Object.keys(data));

Ligatures

Fat pipes manipulate the same object repeatedly:

document.createElement('div')
||> .className = 'civet'
||> .appendChild document.createTextNode 'Civet'

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let ref;
(ref = document.createElement("div")).className =
  "civet";
ref.appendChild(document.createTextNode("Civet"));
ref;

Ligatures

Pipe expression with shorthand functions:

a |> & + 1 |> bar

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bar(a + 1);

Ligatures

Single-Argument Function Shorthand

x.map .name
x.map &.profile?.name[0...3]
x.map &.callback a, b
x.map &+1
x.map -&
x.map [&, &.toUpperCase()]

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x.map(($) => $.name);
x.map(($1) => $1.profile?.name.slice(0, 3));
x.map(($2) => $2.callback(a, b));
x.map(($3) => $3 + 1);
x.map(($4) => -$4);
x.map(($5) => [$5, $5.toUpperCase()]);

Ligatures

Custom Infix Operators

operator {min, max} := Math
value min ceiling max floor

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const { min, max } = Math;
max(min(value, ceiling), floor);

Ligatures

Declarations in Conditions and Loops

if match := regex.exec string
  console.log match

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let ref;
if ((ref = regex.exec(string))) {
  const match = ref;
  console.log(match);
}

Ligatures

Everything is an Expression

items = for item of items
  if item.length
    item.toUpperCase()
  else
    "<empty>"

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const results = [];
for (const item of items) {
  if (item.length) {
    results.push(item.toUpperCase());
  } else {
    results.push("<empty>");
  }
}
items = results;

Ligatures

return
  if x == null
    throw "x is null"
  else
    log `received x of ${x}`
    x.value()

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return (() => {
  if (x == null) {
    throw "x is null";
  } else {
    log(`received x of ${x}`);
    return x.value();
  }
})();

Ligatures

const fs = import {readFile, writeFile} from "fs"

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let ref;
const fs = {
  readFile: (ref = await import("fs")).readFile,
  writeFile: ref.writeFile,
};

Ligatures

TC39 proposal: do expressions

x = do
  const tmp = f()
  tmp * tmp + 1

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let ref;
{
  const tmp = f();
  ref = tmp * tmp + 1;
}
x = ref;

Ligatures

Bulleted Lists and Unbraced Object Literals

projects:
  . name: "Civet"
    url: "https://civet.dev"
  . name: "TypeScript"
    url: "https://www.typescriptlang.org"
colorPairs:
  . . "red"
    . "#f00"
  . . "green"
    . "#0f0"
  . . "blue"
    . "#00f"

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({
  projects: [
    { name: "Civet", url: "https://civet.dev" },
    {
      name: "TypeScript",
      url: "https://www.typescriptlang.org",
    },
  ],
  colorPairs: [
    ["red", "#f00"],
    ["green", "#0f0"],
    ["blue", "#00f"],
  ],
});

Ligatures

Dedented Strings and Templates

TC39 Proposal: String Dedent

text = """
  This text is a string that doesn't include
  the leading whitespace.
"""

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text = `This text is a string that doesn't include
the leading whitespace.`;

Ligatures

text = ```
  Also works for
  ${templates}!
```

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text = `Also works for
${templates}!`;

Ligatures

Chained Comparisons

a < b <= c
value > min?
a is b is not c
a instanceof b not instanceof c

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a < b && b <= c;
min != null && value > min;
a === b && b !== c;
a instanceof b && !(b instanceof c);

Ligatures

Default to `const` for Iteration Items

for (item of [1, 2, 3, 4, 5]) {
  console.log(item * item);
}

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for (const item of [1, 2, 3, 4, 5]) {
  console.log(item * item);
}

Ligatures

Spread in Any Position

Spreads in first or middle position:

[...head, last] = [1, 2, 3, 4, 5]

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([...head] = [1, 2, 3, 4, 5]),
  ([last] = head.splice(-1));

Ligatures

{a, ...rest, b} = {a: 7, b: 8, x: 0, y: 1}

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({ a, b, ...rest } = { a: 7, b: 8, x: 0, y: 1 });

Ligatures

function justDoIt(a, ...args, cb) {
  cb.apply(a, args)
}

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function justDoIt(a, ...args) {
  let [cb] = args.splice(-1);
  return cb.apply(a, args);
}

Ligatures

Import Syntax Matches Destructuring

import {X: LocalX, Y: LocalY} from "./util"

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import { X as LocalX, Y as LocalY } from "./util";

Ligatures

Export Convenience

export a, b, c from "./cool.js"
export x = 3

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export { a, b, c } from "./cool.js";
export var x = 3;

Ligatures

JSX

function Listing(props)
  <h1 #heading>Hello Civet!
  <ul .items>
    <For each=props.items>
      (item) =>
        <li .item {props.style}><Item {item}>

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function Listing(props) {
  return (
    <>
      <h1 id="heading">Hello Civet!</h1>
      <ul class="items">
        <For each={props.items}>
          {(item) => {
            return (
              <li
                class="item"
                style={props.style}
              >
                <Item item={item} />
              </li>
            );
          }}
        </For>
      </ul>
    </>
  );
}

Ligatures

Sponsors

Thank you to all of our sponsors for your invaluable support and contribution to the Civet language!

Support the future development of Civet!

Contributors

Thank you for your work and dedication to the Civet project!