Lazy initialization

lazy.macro.sjs

/*

```
var foo = {
  lazy computed() {
    return [];
  } 
};
```
 
An alternative syntax allows to declare a lazy property on a preexisting object
 
```
var foo = {};
 
lazy foo.property() {
  return [];
};
```
 
*/

macro function_params {
	rule { ($param (,) ...) }
}

macro concise_function_expression {
	rule { $params:function_params { $body ... } } => {
		function $params { $body ... }
	}
	rule { $params:function_params => $body:expr } => {
		function $params { return $body }
	}
}

// cf http://stackoverflow.com/a/22414263
macro syntax2string {
  rule { $syntax } => {
    [makeValue(unwrapSyntax($syntax).toString(), $syntax)]
  }
}
 
macro stringify {
  case { _ ($syntax) } => {
    letstx $string = syntax2string(#{$syntax});
    return #{$string};
  }
}

let lazy = macro {
	rule { $name:ident $function:concise_function_expression } => {
		get $name() {
			return Object.defineProperty(this, stringify($name), {
				__proto__: null,
				value: $function.call(this),
				writable: false,
				enumerable: true,
				configurable: true
			}).$name;
		}
	}
	rule { $symbol:ident (.) ... $name:ident $function:concise_function_expression } => {
		Object.defineProperty($symbol (.) ..., stringify($name), {
			__proto__: null,
			get: function () {
				return Object.defineProperty(this, stringify($name), {
					__proto__: null,
					value: $function.call(this),
					writable: false,
					enumerable: true,
					configurable: true
				}).$name;
			},
			enumerable: true,
			configurable: true
		})
	}
	rule { $rest ... } => { lazy $rest ... }
}

export lazy;