feat: add generator example

Author: guidoschmidt

src/generator.zig

@@ -0,0 +1,88 @@
+/// References:
+/// https://github.com/thi-ng/umbrella/tree/develop/deprecated/packages/iterators
+/// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Iterators_and_generators
+/// https://github.com/ghostty-org/ghostty/blob/main/src/synthetic/Generator.zig
+const std = @import("std");
+const assert = std.debug.assert;
+
+pub const GeneratorError = error{
+    NoSpaceLeft,
+};
+
+fn Generator(comptime T: type, next_fn: fn () T) type {
+    return struct {
+        done: bool = false,
+
+        pub fn next() T {
+            return next_fn();
+        }
+    };
+}
+
+const UrlGenerator = struct {
+    const list_of_urls = [_][]const u8{
+        "https://ziglang.org",
+        "https://zig.news",
+        "https://github.com",
+    };
+
+    pub fn init() type {
+        return Generator(
+            @TypeOf(list_of_urls[0]),
+            struct {
+                var i: usize = 0;
+                const rng_gen = std.Random.DefaultPrng;
+                var rng: std.Random.Xoshiro256 = rng_gen.init(0);
+                const random = rng.random();
+
+                pub fn next_fn() []const u8 {
+                    while (true) {
+                        // if (i >= list_of_urls.len - 1) {
+                        //     i = @mod(i + 1, list_of_urls.len);
+                        // } else {
+                        //     i += 1;
+                        // }
+                        i = random.intRangeAtMost(usize, 0, list_of_urls.len - 1);
+                        return list_of_urls[i];
+                    }
+                }
+            }.next_fn,
+        );
+    }
+};
+
+const FibonacciGenerator = struct {
+    pub fn init(start: usize) type {
+        return Generator(usize, struct {
+            var num_a: usize = start;
+            var num_b: usize = start + 1;
+
+            pub fn next_fn() usize {
+                std.debug.assert(num_a + num_b < std.math.maxInt(usize));
+                const result = num_a + num_b;
+                num_b = num_a;
+                num_a = result;
+                return result;
+            }
+        }.next_fn);
+    }
+};
+
+pub fn main() !void {
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    const allocator = gpa.allocator();
+
+    const url_it = UrlGenerator.init();
+    const fib_it = FibonacciGenerator.init(0);
+    while (true) {
+        std.debug.print("Next URL:\n    → {s}\n", .{url_it.next()});
+        std.debug.print("Fibonnacci:\n    → {d}\n", .{fib_it.next()});
+
+        const in = std.io.getStdIn();
+        var buf = std.io.bufferedReader(in.reader());
+
+        var r = buf.reader();
+        const msg_buf: []u8 = try allocator.alloc(u8, 10);
+        _ = try r.readUntilDelimiter(msg_buf, '\n');
+    }
+}