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采用C语言写的Lua的解释器的代码！Lua不用介绍了吧

           return (h(op))
         else  -- no handler available: default behavior
           error(···)
         end
       end
     end
</pre><p>
See <a href="#2.5.5">&sect;2.5.5</a> for a description of the length of a table.
</li>

<li><b>"eq":</b>
the <code>==</code> operation.

The function <code>getcomphandler</code> defines how Lua chooses a metamethod
for comparison operators.
A metamethod only is selected when both objects
being compared have the same type
and the same metamethod for the selected operation.

<pre>
     function getcomphandler (op1, op2, event)
       if type(op1) ~= type(op2) then return nil end
       local mm1 = metatable(op1)[event]
       local mm2 = metatable(op2)[event]
       if mm1 == mm2 then return mm1 else return nil end
     end
</pre><p>
The "eq" event is defined as follows:

<pre>
     function eq_event (op1, op2)
       if type(op1) ~= type(op2) then  -- different types?
         return false   -- different objects
       end
       if op1 == op2 then   -- primitive equal?
         return true   -- objects are equal
       end
       -- try metamethod
       local h = getcomphandler(op1, op2, "__eq")
       if h then
         return (h(op1, op2))
       else
         return false
       end
     end
</pre><p>
<code>a ~= b</code> is equivalent to <code>not (a == b)</code>.
</li>

<li><b>"lt":</b>
the <code>&lt;</code> operation.


<pre>
     function lt_event (op1, op2)
       if type(op1) == "number" and type(op2) == "number" then
         return op1 &lt; op2   -- numeric comparison
       elseif type(op1) == "string" and type(op2) == "string" then
         return op1 &lt; op2   -- lexicographic comparison
       else
         local h = getcomphandler(op1, op2, "__lt")
         if h then
           return (h(op1, op2))
         else
           error(&middot;&middot;&middot;);
         end
       end
     end
</pre><p>
<code>a &gt; b</code> is equivalent to <code>b &lt; a</code>.
</li>

<li><b>"le":</b>
the <code>&lt;=</code> operation.


<pre>
     function le_event (op1, op2)
       if type(op1) == "number" and type(op2) == "number" then
         return op1 &lt;= op2   -- numeric comparison
       elseif type(op1) == "string" and type(op2) == "string" then
         return op1 &lt;= op2   -- lexicographic comparison
       else
         local h = getcomphandler(op1, op2, "__le")
         if h then
           return (h(op1, op2))
         else
           h = getcomphandler(op1, op2, "__lt")
           if h then
             return not h(op2, op1)
           else
             error(&middot;&middot;&middot;);
           end
         end
       end
     end
</pre><p>
<code>a &gt;= b</code> is equivalent to <code>b &lt;= a</code>.
Note that, in the absence of a "le" metamethod,
Lua tries the "lt", assuming that <code>a &lt;= b</code> is
equivalent to <code>not (b &lt; a)</code>.
</li>

<li><b>"index":</b>
The indexing access <code>table[key]</code>.


<pre>
     function gettable_event (table, key)
       local h
       if type(table) == "table" then
         local v = rawget(table, key)
         if v ~= nil then return v end
         h = metatable(table).__index
         if h == nil then return nil end
       else
         h = metatable(table).__index
         if h == nil then
           error(&middot;&middot;&middot;);
         end
       end
       if type(h) == "function" then
         return (h(table, key))     -- call the handler
       else return h[key]           -- or repeat operation on it
       end
     end
</pre><p>
</li>

<li><b>"newindex":</b>
The indexing assignment <code>table[key] = value</code>.


<pre>
     function settable_event (table, key, value)
       local h
       if type(table) == "table" then
         local v = rawget(table, key)
         if v ~= nil then rawset(table, key, value); return end
         h = metatable(table).__newindex
         if h == nil then rawset(table, key, value); return end
       else
         h = metatable(table).__newindex
         if h == nil then
           error(&middot;&middot;&middot;);
         end
       end
       if type(h) == "function" then
         h(table, key,value)           -- call the handler
       else h[key] = value             -- or repeat operation on it
       end
     end
</pre><p>
</li>

<li><b>"call":</b>
called when Lua calls a value.


<pre>
     function function_event (func, ...)
       if type(func) == "function" then
         return func(...)   -- primitive call
       else
         local h = metatable(func).__call
         if h then
           return h(func, ...)
         else
           error(&middot;&middot;&middot;)
         end
       end
     end
</pre><p>
</li>

</ul>




<h2>2.9 - <a name="2.9">Environments</a></h2>

<p>
Besides metatables,
objects of types thread, function, and userdata
have another table associated with them,
called their <em>environment</em>.
Like metatables, environments are regular tables and
multiple objects can share the same environment.


<p>
Environments associated with userdata have no meaning for Lua.
It is only a convenience feature for programmers to associate a table to
a userdata.


<p>
Environments associated with threads are called
<em>global environments</em>.
They are used as the default environment for their threads and
non-nested functions created by the thread
(through <a href="#pdf-loadfile"><code>loadfile</code></a>, <a href="#pdf-loadstring"><code>loadstring</code></a> or <a href="#pdf-load"><code>load</code></a>)
and can be directly accessed by C&nbsp;code (see <a href="#3.3">&sect;3.3</a>).


<p>
Environments associated with C&nbsp;functions can be directly
accessed by C&nbsp;code (see <a href="#3.3">&sect;3.3</a>).
They are used as the default environment for other C&nbsp;functions
created by the function.


<p>
Environments associated with Lua functions are used to resolve
all accesses to global variables within the function (see <a href="#2.3">&sect;2.3</a>).
They are used as the default environment for other Lua functions
created by the function.


<p>
You can change the environment of a Lua function or the
running thread by calling <a href="#pdf-setfenv"><code>setfenv</code></a>.
You can get the environment of a Lua function or the running thread
by calling <a href="#pdf-getfenv"><code>getfenv</code></a>.
To manipulate the environment of other objects
(userdata, C&nbsp;functions, other threads) you must
use the C&nbsp;API.





<h2>2.10 - <a name="2.10">Garbage Collection</a></h2>

<p>
Lua performs automatic memory management.
This means that
you have to worry neither about allocating memory for new objects
nor about freeing it when the objects are no longer needed.
Lua manages memory automatically by running
a <em>garbage collector</em> from time to time
to collect all <em>dead objects</em>
(that is, these objects that are no longer accessible from Lua).
All objects in Lua are subject to automatic management:
tables, userdata, functions, threads, and strings.


<p>
Lua implements an incremental mark-and-sweep collector.
It uses two numbers to control its garbage-collection cycles:
the <em>garbage-collector pause</em> and
the <em>garbage-collector step multiplier</em>.


<p>
The garbage-collector pause
controls how long the collector waits before starting a new cycle.
Larger values make the collector less aggressive.
Values smaller than 1 mean the collector will not wait to
start a new cycle.
A value of 2 means that the collector waits for the total memory in use
to double before starting a new cycle.


<p>
The step multiplier
controls the relative speed of the collector relative to
memory allocation.
Larger values make the collector more aggressive but also increase
the size of each incremental step.
Values smaller than 1 make the collector too slow and
may result in  the collector never finishing a cycle.
The default, 2, means that the collector runs at "twice"
the speed of memory allocation.


<p>
You can change these numbers by calling <a href="#lua_gc"><code>lua_gc</code></a> in C
or <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> in Lua.
Both get percentage points as arguments
(so an argument of 100 means a real value of 1).
With these functions you can also control 
the collector directly (e.g., stop and restart it).



<h3>2.10.1 - <a name="2.10.1">Garbage-Collection Metamethods</a></h3>

<p>
Using the C&nbsp;API,
you can set garbage-collector metamethods for userdata (see <a href="#2.8">&sect;2.8</a>).
These metamethods are also called <em>finalizers</em>.
Finalizers allow you to coordinate Lua's garbage collection
with external resource management
(such as closing files, network or database connections,
or freeing your own memory).


<p>
Garbage userdata with a field <code>__gc</code> in their metatables are not
collected immediately by the garbage collector.
Instead, Lua puts them in a list.
After the collection,
Lua does the equivalent of the following function
for each userdata in that list:

<pre>
     function gc_event (udata)
       local h = metatable(udata).__gc
       if h then
         h(udata)
       end
     end
</pre>

<p>
At the end of each garbage-collection cycle,
the finalizers for userdata are called in <em>reverse</em>
order of their creation,
among those collected in that cycle.
That is, the first finalizer to be called is the one associated
with the userdata created last in the program.
The userdata itself is freed only in the next garbage-collection cycle.





<h3>2.10.2 - <a name="2.10.2">Weak Tables</a></h3>

<p>
A <em>weak table</em> is a table whose elements are
<em>weak references</em>.
A weak reference is ignored by the garbage collector.
In other words,
if the only references to an object are weak references,
then the garbage collector will collect this object.


<p>
A weak table can have weak keys, weak values, or both.
A table with weak keys allows the collection of its keys,
but prevents the collection of its values.
A table with both weak keys and weak values allows the collection of
both keys and values.
In any case, if either the key or the value is collected,
the whole pair is removed from the table.
The weakness of a table is controlled by the
<code>__mode</code> field of its metatable.
If the <code>__mode</code> field is a string containing the character&nbsp;'<code>k</code>',
the keys in the table are weak.
If <code>__mode</code> contains '<code>v</code>',
the values in the table are weak.


<p>
After you use a table as a metatable,
you should not change the value of its field <code>__mode</code>.
Otherwise, the weak behavior of the tables controlled by this
metatable is undefined.







<h2>2.11 - <a name="2.11">Coroutines</a></h2>

<p>
Lua supports coroutines,
also called <em>collaborative multithreading</em>.
A coroutine in Lua represents an independent thread of execution.
Unlike threads in multithread systems, however,
a coroutine only suspends its execution by explicitly calling
a yield function.


<p>
You create a coroutine with a call to <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>.
Its sole argument is a function
that is the main function of the coroutine.
The <code>create</code> function only creates a new coroutine and
returns a handle to it (an object of type <em>thread</em>);
it does not start the coroutine execution.


<p>
When you first call <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
passing as its first argument
the thread returned by <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>,
the coroutine starts its execution,
at the first line of its main function.
Extra arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> are passed on
to the coroutine main function.
After the coroutine starts running,
it runs until it terminates or <em>yields</em>.


<p>
A coroutine can terminate its execution in two ways:
normally, when its main function returns
(explicitly or implicitly, after the last instruction);
and abnormally, if there is an unprotected error.
In the first case, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>true</b>,
plus any values returned by the coroutine main function.
In case of errors, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>false</b>
plus an error message.


<p>
A coroutine yields by calling <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>.
When a coroutine yields,
the corresponding <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns immediately,
even if the yield happens inside nested function calls
(that is, not in the main function,
but in a function directly or indirectly called by the main function).
In the case of a yield, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> also returns <b>true</b>,
plus any values passed to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>.
The next time you resume the same coroutine,
it continues its execution from the point where it yielded,
with the call to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a> returning any extra
arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.


<p>
Like <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>,
the <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> function also creates a coroutine,
but instead of returning the coroutine itself,
it returns a function that, when called, resumes the coroutine.
Any arguments passed to this function
go as extra arguments to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
<a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> returns all the values returned by <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
except the first on