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modules/meta/index.html
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</nav>
<main>
<h1>Module "meta"</h1>
<p><strong>TODO</strong></p>
<p>This module enables Wren to do certain kinds of meta-programming.</p>
<p>It is an optional module. You can omit it from your application by setting the preprocessor constant <code>WREN_OPT_META</code> to <code>0</code>.</p>
<p>It contains a single class:</p>
<ul>
<li><a href="meta.html">Meta</a></li>
</ul>

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</nav>
<main>
<h1>Meta Class</h1>
<p><strong>TODO</strong></p>
<h2>Methods <a href="#methods" name="methods" class="header-anchor">#</a></h2>
<p><strong>TODO</strong></p>
<p>This class contains static methods to list a module&rsquo;s top-level variables and to compile Wren expressions and source code into closures (i.e. <a href="functions.html">functions</a>) at runtime.</p>
<p>It must be imported from the <a href="meta.html">meta</a> module:</p>
<pre class="snippet">
import "meta" for Meta
</pre>
<h2>Static Methods <a href="#static-methods" name="static-methods" class="header-anchor">#</a></h2>
<h3><strong>getModuleVariables</strong>(module) <a href="#getmodulevariables(module)" name="getmodulevariables(module)" class="header-anchor">#</a></h3>
<p>Returns a list of all module level variables defined or visible in <code>module</code>.</p>
<p>This includes any variables explicitly imported from other modules or implicitly imported from the built-in modules. For example if we create this module:</p>
<pre class="snippet">
/* module.wren */
var M = 1
</pre>
<p>and then import it into this module:</p>
<pre class="snippet">
/* get_mod_vars.wren */
import "meta" for Meta
import "./module" for M
var v = 42
var f = Fn.new {
var g = 2
}
class C {}
System.print(Meta.getModuleVariables("./get_mod_vars"))
var w = 43 // still returned even though defined later
</pre>
<p>the output when the latter module is run is:</p>
<pre class="snippet">
[Object, Class, Object metaclass, Bool, Fiber, Fn, Null, Num, Sequence, MapSequence, SkipSequence, TakeSequence, WhereSequence, List, String, StringByteSequence, StringCodePointSequence, Map, MapKeySequence, MapValueSequence, MapEntry, Range, System, Meta, M, v, f, C, w]
</pre>
<p>Notice that <code>g</code> is not included in this list as it is a local variable rather than a module variable.</p>
<p>It is a runtime error if <code>module</code> is not a string or cannot be found.</p>
<h3><strong>eval</strong>(source) <a href="#eval(source)" name="eval(source)" class="header-anchor">#</a></h3>
<p>Compiles Wren source code into a closure and then executes the closure automatically.</p>
<p>It is a runtime error if <code>source</code> is not a string.</p>
<p>It is also an error if the source code cannot be compiled though the compilation errors themselves are not printed.</p>
<p>For example:</p>
<pre class="snippet">
import "meta" for Meta
var a = 2
var b = 3
var source = """
var c = a * b
System.print(c)
"""
Meta.eval(source) //> 6
</pre>
<h3><strong>compileExpression</strong>(expression) <a href="#compileexpression(expression)" name="compileexpression(expression)" class="header-anchor">#</a></h3>
<p>Compiles a Wren expression into a closure and then returns the closure. It does not execute it.</p>
<p>The closure returns the value of the expression.</p>
<p>It is a runtime error if <code>expression</code> is not a string.</p>
<p>Prints any compilation errors - in which event the closure will be null - but does not throw an error.</p>
<p>For example:</p>
<pre class="snippet">
import "meta" for Meta
var d = 4
var e = 5
var expression = "d * e"
var closure = Meta.compileExpression(expression)
System.print(closure.call()) //> 20
</pre>
<h3><strong>compile</strong>(source) <a href="#compile(source)" name="compile(source)" class="header-anchor">#</a></h3>
<p>Compiles Wren source code into a closure and then returns the closure. It does not execute it.</p>
<p>It is a runtime error if <code>source</code> is not a string.</p>
<p>Prints any compilation errors - in which event the closure will be null - but does not throw an error.</p>
<p>For example:</p>
<pre class="snippet">
import "meta" for Meta
/* Enum creates an enum with any number of read-only static members.
Members are assigned in order an initial integer value (often 0), incremented by 1 each time.
The enum has:
1. static property getters for each member,
2. a static 'startsFrom' property, and
3. a static 'members' property which returns a list of its members as strings.
*/
class Enum {
// Creates a class for the Enum (with an underscore after the name to avoid duplicate definition)
// and returns a reference to it.
static create(name, members, startsFrom) {
if (name.type != String || name == "") Fiber.abort("Name must be a non-empty string.")
if (members.isEmpty) Fiber.abort("An enum must have at least one member.")
if (startsFrom.type != Num || !startsFrom.isInteger) {
Fiber.abort("Must start from an integer.")
}
name = name + "_"
var s = "class %(name) {\n"
for (i in 0...members.count) {
var m = members[i]
s = s + " static %(m) { %(i + startsFrom) }\n"
}
var mems = members.map { |m| "\"%(m)\"" }.join(", ")
s = s + " static startsFrom { %(startsFrom) }\n"
s = s + " static members { [%(mems)] }\n}\n"
s = s + "return %(name)"
return Meta.compile(s).call()
}
}
var Fruits = Enum.create("Fruits", ["orange", "apple", "banana", "lemon"], 0)
System.print(Fruits.banana) //> 2
System.print(Fruits.startsFrom) //> 0
System.print(Fruits.members) //> [orange, apple, banana, lemon]
</pre>
</main>
</div>
<footer>