dart.dx

// Below is a rewrite of the app generated by `flutter create` using a
// hypothetical syntax for a Flutter-oriented Dart language extension,
// called dx (file extension .dx).
//
// Key properties of the language:
//
// - Valid Dart is also valid .dx (start by renaming .dart to .dx).
// - Transpiles file-by-file to plain Dart (syntax translation only).
// - Start with strong-mode Dart syntax/semantics, then:
// - Add Flutter-specific keywords: widget, state, build.
// - Add immutable data type keyword: value.
// - Widgets and values are:
//   - Immutable (can we make it deep?).
//   - Fields are non-nullable by default (enforced by asserts).
// - Add Flutter-specific semantics:
//   - infer setState()
//   - infer widget.
// - Immutable collection literals
// - Add argument-initializer blocks (a.k.a. builder syntax).
// - No new, elidable const
// - Reduce variety of parens (https://goo.gl/gBxJSz).
// - Reduce punctuation (optional semi-colons) (https://goo.gl/gBxJSz).
// - Reduce `import` boilerplate.

import {
  flutter/material  // semi-colons optional, but only inside new syntax
}

// Old-style imports work too, but discouraged:
import 'package:flutter/foundation.dart';

/// A stateless widget.
widget MyApp {
  build {
    MaterialApp {
      // := means assign to named parameter of enclosing constructor call.
      title := 'Flutter Demo'

      theme := ThemeData {
        primarySwatch := Colors.blue
      }

      home := MyHomePage {
        title := 'Flutter Demo Home Page'
        countFrom := 5
      }
    }
  }
}

/// A stateful widget.
widget MyHomePage {
  Key? key -> super.key  // open to ideas here
  String? title = 'Default value'
  int countFrom

  // Properties inside state are mutable.
  state {
    int _counter = countFrom
  }

  build {
    Scaffold {
      appBar := AppBar {
        // widget.title inferred lexically.
        title := Text(title)
      }

      body := Center {
        child := Column {
          mainAxisAlignment := MainAxisAlignment.center
          children := [
            Text('You have pushed the button this many times:'),
            Text('${_counter}') {
              style := Theme.of(context).textTheme.display1
            },
          ]
        }
      }

      floatingActionButton := FloatingActionButton {
        onPressed := () {
          // `setState(() { ... })` inferred lexically from `state.`
          state._counter++
        }
        tooltip := 'Increment'
        child := Icon(Icons.add)
      }
    }
  }
}

/// A value type is:
///
/// - Immutable:
///   - No setters.
///   - How easy is it to enforce deep immutability?
/// - NNBD.
/// - Has constructor with named parameters matching fields.
/// - Has auto-generated hashCode/==.
/// - Has auto-generated copy constructor.
value Employee {
  String firstName
  String? lastName
  DateTime dateOfBirth

  int get age => DateTime.now().difference(dateOfBirth).inDays / 365
  String get fullName => '$firstName $lastName'
}

// Plain-old Dart works:

Employee updateLastName(Employee original, String newLastName) => original.copy(
  lastName: newLastName,
);

class HumanResourcesService {
  final List<Employee> _employees = <Employee>[];
  
  void add(Employee employee) {
    _employees.add(employee);
  }
}