blah.rs

## highlight: ship

Error propagation example checks production, propagation, partial handling, residual handling, and sealing.

  $ ship check --show-types bin/main.shp
    type ConfigErrors = [ :missing_env(String) | :invalid_port(String) | :invalid_region(String) ]
    type OrderErrors = [ :order_not_found(String) | :db_timeout(Int) | :db_corrupt(String) ]
    type PaymentErrors = [ :card_declined(String) | :gateway_timeout(Int) | :fraud_hold(String) ]
    
    let read_env = fn(name: String) -> String? [ :missing_env(String) ] {
  //    ^^^^^^^^ fn(String) -> String? [ :missing_env(String) ]
  //                  ^^^^ String
      if (name == "PROTECTED") {
  //      ^^^^ String
  //              ^^^^^^^^^^^ String
        error :missing_env(name);
  //                       ^^^^ String
      }
    
      return "5432";
  //         ^^^^^^ String
    }
    
    let parse_port = fn(raw: String) -> Int? [ :invalid_port(String) ] {
  //    ^^^^^^^^^^ fn(String) -> Int? [ :invalid_port(String) ]
  //                    ^^^ String
      return match Int.parse(raw) {
  //               ^^^^^^^^^ fn(String) -> Int? [> :parse(String) ]
  //                         ^^^ String
        | value -> value
  //      ^^^^^ Int
  //               ^^^^^ Int
        | error e -> { error :invalid_port("${e}"); }
  //            ^ [> :parse(String) ]
  //                                          ^ [> :parse(String) ]
      }
    }
    
    let parse_region = fn(raw: String) -> String? [ :invalid_region(String) ] {
  //    ^^^^^^^^^^^^ fn(String) -> String? [ :invalid_region(String) ]
  //                      ^^^ String
      if (raw == "us-east-1") {
  //      ^^^ String
  //             ^^^^^^^^^^^ String
        error :invalid_region(raw);
  //                          ^^^ String
      }
    
      return "us-east";
  //         ^^^^^^^^^ String
    }
    
    let load_config = fn() -> String? [ ConfigErrors ] {
  //    ^^^^^^^^^^^ fn() -> String? [ ConfigErrors ]
      let port_text = read_env("DATABASE_PORT");
  //      ^^^^^^^^^ String
  //                  ^^^^^^^^ fn(String) -> String? [ :missing_env(String) ]
  //                           ^^^^^^^^^^^^^^^ String
      let port = parse_port(port_text);
  //      ^^^^ Int
  //             ^^^^^^^^^^ fn(String) -> Int? [ :invalid_port(String) ]
  //                        ^^^^^^^^^ String
      let region = parse_region("us-east");
  //      ^^^^^^ String
  //               ^^^^^^^^^^^^ fn(String) -> String? [ :invalid_region(String) ]
  //                            ^^^^^^^^^ String
      return "${region}:${port}";
  //            ^^^^^^ String
  //                      ^^^^ Int
    }
    
    let load_config_or_default = fn() {
  //    ^^^^^^^^^^^^^^^^^^^^^^ fn() -> String? [ ConfigErrors - :missing_env ]
      return try load_config() {
  //             ^^^^^^^^^^^ fn() -> String? [ ConfigErrors ]
        | :missing_env(name) -> "local:5432"
  //                   ^^^^ String
  //                            ^^^^^^^^^^^^ String
      };
    }
    
    let load_config_or_message = fn() {
  //    ^^^^^^^^^^^^^^^^^^^^^^ fn() -> String
      return try load_config_or_default() {
  //             ^^^^^^^^^^^^^^^^^^^^^^ fn() -> String? [ ConfigErrors - :missing_env ]
        | rest -> "config unavailable"
  //      ^^^^ [ ConfigErrors - :missing_env ]
  //              ^^^^^^^^^^^^^^^^^^^^ String
      };
    }
    
    let lookup_order = fn(order_id: String) -> String? [ OrderErrors ] {
  //    ^^^^^^^^^^^^ fn(String) -> String? [ OrderErrors ]
  //                      ^^^^^^^^ String
      error :order_not_found(order_id);
  //                         ^^^^^^^^ String
      error :db_timeout(30);
  //                    ^^ Int
      error :db_corrupt("orders");
  //                    ^^^^^^^^ String
      return "order:${order_id}";
  //                  ^^^^^^^^ String
    }
    
    let render_order_summary = fn(order_id: String) {
  //    ^^^^^^^^^^^^^^^^^^^^ fn(String) -> String? [ OrderErrors - :order_not_found ]
  //                              ^^^^^^^^ String
      return match lookup_order(order_id) {
  //               ^^^^^^^^^^^^ fn(String) -> String? [ OrderErrors ]
  //                            ^^^^^^^^ String
        | order -> "loaded ${order}"
  //      ^^^^^ String
  //                         ^^^^^ String
        | error :order_not_found(missing_id) -> "missing order ${missing_id}"
  //                             ^^^^^^^^^^ String
  //                                                             ^^^^^^^^^^ String
      };
    }
    
    let render_order_or_queue = fn(order_id: String) {
  //    ^^^^^^^^^^^^^^^^^^^^^ fn(String) -> String
  //                               ^^^^^^^^ String
      return try render_order_summary(order_id) {
  //             ^^^^^^^^^^^^^^^^^^^^ fn(String) -> String? [ OrderErrors - :order_not_found ]
  //                                  ^^^^^^^^ String
        | rest -> "order queued for review"
  //      ^^^^ [ OrderErrors - :order_not_found ]
  //              ^^^^^^^^^^^^^^^^^^^^^^^^^ String
      };
    }
    
    let charge_card = fn(order: String) -> String? [ PaymentErrors ] {
  //    ^^^^^^^^^^^ fn(String) -> String? [ PaymentErrors ]
  //                     ^^^^^ String
      return match order {
  //               ^^^^^ String
        | "slow" -> { error :gateway_timeout(30); }
  //                                         ^^ Int
        | "broke" -> { error :card_declined(order); }
  //                                        ^^^^^ String
        | "stealing" -> { error :fraud_hold(order); }
  //                                        ^^^^^ String
        | order -> "receipt:${order}"
  //      ^^^^^ String
  //                          ^^^^^ String
      };
    }
    
    let checkout = fn(order_id: String) {
  //    ^^^^^^^^ fn(String) -> String? [ :db_corrupt(String) | :db_timeout(Int) | :fraud_hold(String) | :gateway_timeout(Int) | :order_not_found(String) ]
  //                  ^^^^^^^^ String
      let order = lookup_order(order_id);
  //      ^^^^^ String
  //              ^^^^^^^^^^^^ fn(String) -> String? [ OrderErrors ]
  //                           ^^^^^^^^ String
      return try charge_card(order) {
  //             ^^^^^^^^^^^ fn(String) -> String? [ PaymentErrors ]
  //                         ^^^^^ String
        | :card_declined(declined_order) -> "ask for another card"
  //                     ^^^^^^^^^^^^^^ String
  //                                        ^^^^^^^^^^^^^^^^^^^^^^ String
      };
    }
    
    let checkout_or_ticket = fn(order_id: String) {
  //    ^^^^^^^^^^^^^^^^^^ fn(String) -> String
  //                            ^^^^^^^^ String
      return try checkout(order_id) {
  //             ^^^^^^^^ fn(String) -> String? [ :db_corrupt(String) | :db_timeout(Int) | :fraud_hold(String) | :gateway_timeout(Int) | :order_not_found(String) ]
  //                      ^^^^^^^^ String
        | rest -> "support ticket"
  //      ^^^^ [ :db_corrupt(String) | :db_timeout(Int) | :fraud_hold(String) | :gateway_timeout(Int) | :order_not_found(String) ]
  //              ^^^^^^^^^^^^^^^^ String
      };
    }
    
    let health = fn() -> String! {
  //    ^^^^^^ fn() -> String!
      return "ok";
  //         ^^^^ String
    }
    
    let main = fn() {
  //    ^^^^ fn() -> Unit
      print(load_config_or_message());
  //  ^^^^^ fn(...'a, ~sep: String, ~end: String) -> Unit
  //        ^^^^^^^^^^^^^^^^^^^^^^ fn() -> String
      print(render_order_or_queue("order-404"));
  //  ^^^^^ fn(...'a, ~sep: String, ~end: String) -> Unit
  //        ^^^^^^^^^^^^^^^^^^^^^ fn(String) -> String
  //                              ^^^^^^^^^^^ String
      print(checkout_or_ticket("order-500"));
  //  ^^^^^ fn(...'a, ~sep: String, ~end: String) -> Unit
  //        ^^^^^^^^^^^^^^^^^^ fn(String) -> String
  //                           ^^^^^^^^^^^ String
      print(health());
  //  ^^^^^ fn(...'a, ~sep: String, ~end: String) -> Unit
  //        ^^^^^^ fn() -> String!
    }

The same example runs with expected errors short-circuiting through calls and handlers.

  $ ship run .
  us-east:5432
  missing order order-404
  support ticket
  ok