Katnip

A typed programming language that compiles to Scratch. You write .knip files, run the compiler, and get a .sb3 project that opens in Scratch or MistWarp or TurboWarp and runs like any other project.

public score: num = 0;

proc award(points: num) -> void {
    score += points;
}

sprite Cat {
    events.onFlag() {
        pen.down();
        for (side, 4) {
            motion.forward(100);
            motion.turn(90);
            award(10);
        }
        pen.up();
        looks.say(f"Scored {score}!", 2);
    }
}

That builds into a real Scratch project: a stage variable score, a custom block award, a green-flag script on the Cat sprite, and the pen extension enabled.

npm install -g @katnip-org/compiler
katnip build hello.knip

Node.js 20+. See the documentation to get started, or @katnip-org/compiler for the CLI and library reference.

pnpm install
pnpm build
node packages/compiler/build/cli.js help

Run the test suite (~180 tests across lexer, parser, semantic, IR, and codegen):

pnpm test

End-to-end example covering everything the compiler lowers today:

node packages/compiler/build/cli.js build examples/codegen.knip

Live diagnostics, highlighting, and autocomplete for .knip files. Build the .vsix (rebuilds and vendors the compiler, then packages):

pnpm --filter katnip-vscode run package
code --install-extension packages/vscode/katnip-vscode-0.0.14.vsix --force

Run Developer: Reload Window, then open any .knip file.

source → lexer → parser → semantic analysis → IR → SB3 → .sb3

The frontend type-checks, the IR reconciles Katnip's semantics with what Scratch can actually express (tuple returns, ranged for, switch -- none of which exist as blocks), and the SB3 generator emits the block JSON that gets zipped into a .sb3.

Not yet lowered to blocks: structs, slices, **, and some katnip_* builtins. features.md tracks the gaps.

Apache-2.0 -- see LICENSE and NOTICE.