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Narcissus/Development: Difference between revisions
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interpreter info
(another host-lang req, more in the interpreter) |
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=== Values === | === Values === | ||
User-JS primitive values are represented in host-JS directly as themselves. | |||
User-JS objects are represented directly as host-JS objects; each user-property <code>foo</code> is directly represented as a host-property <code>foo</code>. | |||
User-JS functions are represented as proxy functions that wrap a <code>FunctionObject</code>, which encapsulates the <code>Node</code> and <code>ExecutionContext</code> for the closure. | |||
=== Control flow === | === Control flow === | ||
Code is always executed with a current <code>ExecutionContext</code>, which contains the current scope chain and <code>this</code> binding. Execution contexts also contain a <code>result</code> property, which is used for the completion value of the current statement or expression or the result of returning from a function or throwing an exception. | |||
Calling a user-JS function is represented by calling the host-JS <code>__call__</code> method. Narcissus patches the host-JS <code>Function.prototype</code> to add a default <code>__call__</code> method. Similarly, calling a user-JS function as a constructor (i.e., from <code>new</code>) is represented by calling the host-JS <code>__construct__</code> method. '''This is unnecessary now that functions are proxies; see [https://bugzilla.mozilla.org/show_bug.cgi?id=586095 bug 586095].''' | |||
Returning from a function via <code>return</code> is represented by throwing the constant <code>RETURN</code>. The return value is stored in the <code>result</code> property of the current execution context. | |||
Throwing a user-JS exception is represented by throwing the constant <code>THROW</code>. The exception value is stored in the <code>result</code> property of the current execution context. | |||
Breaking or continuing a loop is represented by throwing the constant <code>BREAK</code> or <code>CONTINUE</code>, respectively. | |||