Compile-time functions

The trusted @CompileTime attribute marks a function that may run during compilation:

@CompileTime
function doubled(value: Int): Int
    return value * 2
end

const BUFFER_SIZE: Int = doubled(512)

Here the call is evaluated by the compiler, and BUFFER_SIZE becomes 1024 before runtime code is emitted. Runtime uses of the constant receive that already evaluated Int; there is no runtime lookup or mutable global.

Compile-time functions can support constant declarations, field defaults, attribute arguments, and attribute validators. Their parameters and results still use ordinary Pop types, and their bodies are type-checked like other functions.

Closed compile-time calls

A compile-time function cannot call arbitrary runtime code. Every Pop function it calls must also be marked @CompileTime:

function runtimeOnly(): Int
    return 42
end

@CompileTime
function invalid(): Int
    return runtimeOnly() -- rejected
end

This closed call graph keeps compile-time execution independent of runtime-only effects. The compiler also detects recursive evaluation cycles and enforces resource limits so a bad constant computation cannot run forever.

Conditional expressions preserve lazy evaluation at compile time:

@CompileTime
function choose(flag: Boolean): Int
    return if flag then 42 else 1 / 0
end

const ANSWER = choose(true)

The unselected division is not evaluated.

Compile-time functions are removed from the runtime MIR when they exist only for compilation. Do not use @CompileTime as a performance hint for an ordinary runtime helper; use it when the function’s intended environment truly is the compiler.