Lexical Structure

RSS source is UTF-8 text. Whitespace separates tokens, comments are discarded, and semicolons terminate statements where the grammar requires them.

Line comments

// continues to the end of the current line.

// A complete line comment.
let answer = 42; // A trailing comment.
answer;

Block comments

/ ... / may span lines.

/* Compute the public result.
   This comment spans two lines. */
let answer = 40 + 2;
answer;

Identifiers

Identifiers begin with an ASCII letter or _ and continue with ASCII letters, digits, or _.

let answer_42 = 42;
let _internal = answer_42;
let final_result = _internal;
final_result;

Keywords

Reserved words introduce declarations and control flow. Type names such as int and string are schema identifiers interpreted in type position.

pub fn choose(value: int?) -> int {
    match value {
        Some(found) => found,
        None => 0,
        _ => 0,
    }
}
let mut result = choose(42);
result;

Integer literals

Integers are decimal or hexadecimal. The accepted range is signed 64-bit.

let decimal = 42;
let hexadecimal = 0x2A;
let minimum = -9223372036854775808;
decimal + hexadecimal + minimum;

Floating-point literals

A decimal point followed by at least one digit produces a float literal.

let one = 1.0;
let fraction = 0.125;
let negative = -2.5;
one + fraction + negative;

String literals and escapes

Single and double quotes both create strings. Supported escapes include \n, \r, \t, \\, \", \', \0, and two-digit \xNN.

let double_quoted = "line 1\nline 2";
let single_quoted = 'RustScript';
let escaped = "\x52\x53\x53\0";
double_quoted + single_quoted + escaped;

Byte literals and escapes

Prefix a double-quoted literal with b to create bytes. Byte escapes use the same spellings and \xNN inserts one byte.

let header = b"RSS\x00";
let control = b"\n\t";
header.length + control.length;

Delimiters and punctuation

Parentheses group expressions and calls, braces delimit blocks and maps, brackets delimit arrays and indexes, commas separate items, colons attach schemas or values, and :: selects namespace members.

use math;
let values: array<int> = [1, 2, 3];
let record = {answer: values[0] + values[1]};
math::max(record.answer, values[2]);

Statement semicolons

Bindings, assignments, calls used as statements, break, and continue end with ;.

let mut value = 0;
value = 41;
value += 1;
value;

Trailing result expressions

A function body or expression branch returns its final expression without requiring a trailing semicolon.

fn answer() -> int {
    let base = 40;
    base + 2
}
let value = if true => { answer() } else => { 0 };
value;

Source files

The native source extension is .rss. pd-vm-run accepts a file directly.

// hello.rss
fn greeting(name: string) -> string {
    "hello, " + name
}
greeting("RSS");