Contrast Language (created with AI)

A small JavaScript-inspired language for building APIs, written in C, so programs run as a native compiled binary — no JS runtime needed. Ships with an Express-style HTTP server built into the language.

Build

Single-file C, no third-party deps (just libm + the OS sockets lib).

cc -O2 -o contrast contrast.c -lm                  # gcc / clang / *nix
zig cc -O2 -o contrast.exe contrast.c -lws2_32     # zig on Windows (self-contained)

On Windows you can also just run build.bat.

Run

./contrast example.con   # run a file
./contrast api.con       # start the API server demo
./contrast               # start the REPL

In the REPL, bare expressions print their value (=> ...), multi-line blocks (fn, if, while) continue with a ... prompt until braces balance, and a runtime error reports the line without killing the session.

Syntax

Variables

con replaces var/let/const:

con one = 1
con text = "Text"
one = 2          // reassignment

Methods (built-ins)

log("test")           // normal output
warn("warning")       // yellow
err("error")          // red
contrast("#000000")   // WCAG contrast ratio + recommended text color
len(x)                // length of an array or string
push(arr, value)      // append to an array, returns new length

contrast(color) returns the ratio (a number), so you can store it:

con r = contrast("#3498db")

Functions

fn declares a function; return yields a value. Functions are first-class values (pass them around, recurse, close over scope):

fn add(a, b) { return a + b }
fn fib(n) {
  if < n <= 1 > { return n }
  return fib(n - 1) + fib(n - 2)
}
fn apply(f, x) { return f(x) }   // f is a function value

Arrays

Literals, indexing, and index assignment:

con nums = [1, 2, 3]
push(nums, 4)        // [1, 2, 3, 4]
nums[0] = 10         // [10, 2, 3, 4]
log(nums[2], len(nums))

Strings can be indexed too: "Text"[0] is "T".

Objects

Object literals use { key: value }; read/write with . or ["key"]:

con user = { name: "Ada", age: 36 }
log(user.name)        // Ada
user.age = 37
user["role"] = "dev"

(A { ... } that doesn't start with key: is a function block instead.)

HTTP server (Express-style)

Route handlers are blocks { ... } with req and res in scope:

get("/", {
  res.send("Olá Mundo!")
})

get("/json", {
  res.json({ name: "contrast", fast: true })
})

post("/email", {
  res.status(201).json({ ok: true, received: req.body })
})

put("/user",    { res.json({ updated: true }) })
delete("/movie",{ res.status(204).send() })

listen(3000, { log("server ready") })

• Routes: get, post, put, delete — each takes (path, handler).
• req fields: req.method, req.path, req.url, req.query, req.body.
• res methods: res.send(x) (string → HTML, object/array → JSON), res.json(x), res.status(code) (chainable), res.set(name, value).
• listen(port, callback) starts the blocking server; the callback runs once.
• A handler can also be a named fn(req, res) { ... }.

Conditions

A condition goes inside < >. Inside it, = means equality:

if < text = "Text" > {
  log("matches")
} else {
  err("no match")
}

Loop

con i = 0
while < i <= 2 > {
  log(i)
  i = i + 1
}

Operators

• arithmetic: + - * / % (+ also concatenates strings)
• equality: = or ==, !=
• comparison: <=, >= (< and > are condition delimiters)
• logical: &&, ||, !

Types

number, string, true, false, null, array, object, function

Comments: // ...

How it works

contrast.c is a tree-walking interpreter: lexer -> recursive-descent parser -> AST -> evaluator. The HTTP server uses raw BSD/Winsock sockets, parses the request line + headers, builds the req/res objects, and dispatches to the matching route.