094 template per call arg substitution

// Test: per-call template with captured-argument substitution.
// `~count_to(n: 3)` captures `3` as the Expression text for `n`. The
// template interpolates `{{ n }}` into the Zig body. Each call site
// substitutes ITS captured value, so this is the foundation of macro-
// shaped events like `for`, `if`, etc.

const std = @import("std");

~pub event count_to { n: i32 }

~proc count_to|template|zig {
    var i: i32 = 0;
    while (i < {{ n }}) : (i += 1) {
        std.debug.print("{d}\n", .{i});
    }
}

~count_to(n: 3)