verified-functions.md

Walkthrough: print, call, and define functions

This tutorial is built from real compiler-owned programs in Scarp v0.0.5-alpha.1. Each source block and its expected stdout below is checked against the pinned conformance suite in CI. It documents the published interpreter, not a future native-code compiler.

Before starting, install the prerelease, then confirm scarp --version reports 0.0.5-alpha.1. If you're using a source checkout, replace scarp with cargo run --.

1. Run the smallest example

Create hello.srp and copy all of the following source:

// My first Scarp program
print("Hello from Scarp!");

Run scarp check hello.srp first, then scarp run hello.srp to display:

Hello from Scarp!

What happened? The print statement writes text and a newline to standard output. check validates the selected execution path silently; it does not print the program's output. Read about output streams.

Compiler evidence: hello.srp and its expected stdout.

2. Explore typed functions

Create functions.srp and copy this complete, published compiler example. funcra defines a function, parameters have explicit types, and -> declares the result type. Note that the first call occurs before the function definition: the published interpreter resolves these named functions.

// Typed calls, forward declarations, all primitive parameter types, and unit.
print(add(10, square(5)));

funcra add(a: integer, b: integer) -> integer {
    return a + b;
}

funcra square(value: integer) -> integer {
    return value * value;
}

funcra identity(text: string) -> string {
    return text;
}

funcra greet(name: string) -> unit {
    print("Hello", name);
    return;
}

pure funcra choose(value: integer, enabled: boolean) -> integer {
    if enabled { return value * 2; }
    return value;
}

greet(identity("Scarp"));
print(choose(3, true));

Run scarp check functions.srp and then scarp run functions.srp. Expected standard output, line for line:

35
Hello Scarp
6

Read the output

1. square(5) returns 25; add(10, 25) returns 35.
2. identity("Scarp") returns a string, and greet writes Hello Scarp before returning unit (no value).
3. choose(3, true) returns 6; the pure modifier places restrictions on the function's allowed effects.

Compiler evidence: functions.srp and its expected stdout.

3. Learn to change code safely

Try changing the first arguments of add and square, then run scarp check functions.srp and scarp run functions.srp again. The checked example above is the unchanged reference version; your experiment's output will differ. Next, try a wrong argument type and read the diagnostic. See function semantics and diagnostics.

Why these examples are trustworthy

The docs repository mirrors these exact source/output pairs from the pinned compiler release. The documentation's TypeScript evidence check ensures that this page and its Hindi counterpart still display the mirrored source and expected output, in order. In a separate GitHub Actions job, the actual published interpreter executes the same files and its output is compared byte-for-byte.

This does not guarantee arbitrary modified programs will work or that future releases will preserve the syntax. Refer to feature status and the source-of-truth policy.

Continue with loops, source modules, or the beginner glossary.