const std = @import("std");
const typeVerify = @import("util.zig").typeVerify;

/// ```zig
/// (fn (fn (fn (a) bool, []a) []a)
/// ```
/// Filters a slice, only keeping items give `true` when passed into `func`
/// Type signature: `(a -> bool) -> [a] -> [a]`
/// `func` is of type `a -> bool`, where `items` is of type `[a]`
pub fn filter(
    func: anytype,
    items: []typeVerify(@TypeOf(func), .{ .@"fn" }).@"fn".params[0].type.?,
) []typeVerify(@TypeOf(func), .{ .@"fn" }).@"fn".params[0].type.? {
    var output = items;
    var i: u32 = 0;
    for (items) |it|
        if (func(it)) {
            output[i] = it;
            i = i + 1;
        };
    return output[0..i];
}