050 transform impl pattern

const std = @import("std");
const ast = @import("ast");
const Program = ast.Program;
const Item = ast.Item;

~[keyword|comptime|transform]pub tor sample-transform {
    item: *const Item,
    program: *const Program,
    allocator: std.mem.Allocator
} -> SiteResult

~[norun]pub tor sample-impl {}

~proc sample-transform|zig {
    // Deriving flow from item
    const flow = if (item.* == .flow)
        &item.flow
    else
        return .{};

    const segments = allocator.alloc([]const u8, 1) catch unreachable;
    segments[0] = "sample-impl";
    
    var new_inv = flow.inv().*;
    new_inv.path = ast.DottedPath{
        .segments = segments,
        .module_qualifier = "input"
    };
    new_inv.annotations = &[_][]const u8{ "@pass_ran(\"transform\")" };

    const transformed_flow = ast.Flow{
        .body = ast.rootSite(new_inv, flow.body.continuations, flow.location),
        .inline_body = "    // lowered\n",
        .location = flow.location,
        .module = flow.module,
    };
    return .{ .replacement = .{ .flow = transformed_flow } };
}

~sample-transform()