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comptime_closures

Closures without a GC: a closure passed to a comptime parameter is compiled into its own instance of the function, which gets the captured values as hidden arguments and calls the closure directly, like Rust’s impl Fn.

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jihoo build examples/comptime_closures.jh -o out/cc && ./out/cc
examples/comptime_closures.jh
#![freestanding]
import io


fn each(comptime f: fn(i64), xs: [i64; 5]) {
    let i = 0
    while i < len(xs) {
        f(xs[i])
        i = i + 1
    }
}


fn count(comptime keep: fn(i64) -> bool, xs: [i64; 5]) -> i64 {
    let n = 0
    // A closure can be passed on, or wrapped in another one.
    each(fn(x) {
        if keep(x) {
            io.print_int(x)
        }
    }, xs)
    let i = 0
    while i < len(xs) {
        if keep(xs[i]) {
            n = n + 1
        }
        i = i + 1
    }
    return n
}


fn _start() -> i64 {
    let xs = [12, 7, 30, 1, 18]
    let limit = 10
    let n = count(fn(x) { return x > limit }, xs)   // prints 12, 30, 18
    return n                                         // exit status 3
}

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