Lua

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### Task Usage Example

Source: https://www.lua.org/notes/ltn003.html

Example of initializing a task and setting up event handlers.

```lua
mytask = w_task("MyTask",310, { [0] = M_DataLoad, [1] = M_Quit })
  .....................
    
  mytask.action[Mouse_Click] = function (self) ........ end
  .....................
                                 
  mytask:poll()
```

--------------------------------

### Buffer Initialization Example

Source: https://www.lua.org/notes/ltn003.html

Example of initializing arrays and writing data into them.

```lua
x,y = array(n),array(m)



  x:chars { [0] = "hello".."\0" } -- only 6 bytes taken up so far
  x:words { [2] = a_num, [3] = y }
```

--------------------------------

### Perform a GET request with http.request

Source: https://www.lua.org/wshop17/lua-http.html

This example demonstrates how to create a request from a URI, execute it, iterate over the response headers, and retrieve the body as a string.

```lua
local http_request = require "http.request"
local my_req = http_request.new_from_uri("http://httpbin.org/get")
local headers, stream = assert(my_req:go())
for field, value in headers:each() do
    print(field, value)
end
local body = assert(stream:get_body_as_string())
print(body)
```

--------------------------------

### Variadic Function Examples

Source: https://www.lua.org/manual/5.5/manual.html

Example function definitions for testing argument mapping.

```Lua
     function f(a, b) end
     function g(a, b, ...) end
     function r() return 1,2,3 end
```

--------------------------------

### Table Constructor Example and Equivalent Assignments

Source: https://www.lua.org/manual/5.5/manual.html

An example of a table constructor and the equivalent sequence of assignments.

```lua
     a = { [f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45 }
```

```lua
     do
       local t = {}
       t[f(1)] = g
       t[1] = "x"         -- 1st exp
       t[2] = "y"         -- 2nd exp
       t.x = 1            -- t["x"] = 1
       t[3] = f(x)        -- 3rd exp
       t[30] = 23
       t[4] = 45          -- 4th exp
       a = t
     end
```

--------------------------------

### Create and use an Account instance

Source: https://www.lua.org/pil/16.1.html

Shows how to instantiate a new account and call a method on it.

```lua
    a = Account:new{balance = 0}
    a:deposit(100.00)
```

--------------------------------

### Check if string starts with a digit using string.find and pattern ^%d

Source: https://www.lua.org/pil/20.2.html

This example uses the ^ anchor to test if the string s begins with a digit. The pattern ^%d matches a digit only at the start of the string.

```lua
    if string.find(s, "^%d") then ...

```

--------------------------------

### Read overflow in 'l_strcmp' - Lua example

Source: https://www.lua.org/bugs.html

This example triggers a read overflow in 'l_strcmp' when the locale 'km_KH.UTF-8' is installed. It compares two strings with a large repetition and a null character.

```Lua
-- You must have the locale 'km_KH.UTF-8' installed
assert(os.setlocale("km_KH.UTF-8"))
local A = "\u{17A4}"
local B = "\u{17A2}\u{17B6}"
print(string.rep(B, 100000) .. "\0" <= string.rep(A, 100000) .. "\0")

```

--------------------------------

### Running the pipeline step by step

Source: https://www.lua.org/pil/9.2.html

Shows how to run the complete pipeline by creating the producer, filter, and consumer in sequence.

```lua
    p = producer()
    f = filter(p)
    consumer(f)

```

--------------------------------

### Define Named Class

Source: https://www.lua.org/pil/16.3.html

An example class Named with methods for setting and getting a name.

```lua
    Named = {}
    function Named:getname ()
      return self.name
    end
    
    function Named:setname (n)
      self.name = n
    end
```

--------------------------------

### Lua Configuration File Example

Source: https://www.lua.org/pil/25.1.html

A sample Lua configuration file defining global variables for window dimensions and background color components.

```lua
    -- configuration file for program `pp'
    width = 200
    height = 300
    background_red = 0.30
    background_green = 0.10
    background_blue = 0
```

--------------------------------

### memory.get

Source: https://www.lua.org/wshop18/Maia

Gets one or more bytes from a memory object starting at a given index. Returns the byte value(s) as numbers.

```APIDOC
## memory.get

### Description
Gets one or more bytes from a memory object starting at a given index. Returns the byte value(s) as numbers.

### Method
Function call

### Endpoint
memory.get(mem, start, [count])

### Parameters
- **mem** (userdata) - Required - The memory object.
- **start** (number) - Required - The starting index (1-based).
- **count** (number) - Optional - The number of bytes to get. If omitted, returns a single byte.

### Return Value
- **byte1, byte2, ...** (number) - The byte values.

### Example
```lua
assert(memory.get(eight, 8) == 0xef)
local a, b, c = memory.get(eight, 3, 5)
```
```

--------------------------------

### Crash when getting active-line information for a vararg function with no debug information - Lua example

Source: https://www.lua.org/bugs.html

This Lua snippet crashes when calling debug.getinfo on a stripped function that is vararg. It loads a function, strips its debug info, and then tries to get active lines.

```Lua
sample = 'print("hello")'
stripped = load(string.dump(load(sample), true))
print(debug.getinfo(stripped, "L").activelines)

```

--------------------------------

### luaopen_io initialization

Source: https://www.lua.org/source/5.5/liolib.c.html

Entry point for the I/O library, initializing the module and standard files.

```c
LUAMOD_API int luaopen_io (lua_State *L) {
  luaL_newlib(L, iolib);  /* new module */
  createmeta(L);
  /* create (and set) default files */
  createstdfile(L, stdin, IO_INPUT, "stdin");
  createstdfile(L, stdout, IO_OUTPUT, "stdout");
  createstdfile(L, stderr, NULL, "stderr");
  return 1;
}
```

--------------------------------

### luaopen_package initialization

Source: https://www.lua.org/source/5.5/loadlib.c.html

The entry point for opening the package library, setting up paths, searchers, and global tables.

```c
LUAMOD_API int luaopen_package (lua_State *L) {
  luaL_getsubtable(L, LUA_REGISTRYINDEX, CLIBS);  /* create CLIBS table */
  lua_pop(L, 1);  /* will not use it now */
  luaL_newlib(L, pk_funcs);  /* create 'package' table */
  createsearcherstable(L);
  /* set paths */
  setpath(L, "path", LUA_PATH_VAR, LUA_PATH_DEFAULT);
  setpath(L, "cpath", LUA_CPATH_VAR, LUA_CPATH_DEFAULT);
  /* store config information */
  lua_pushliteral(L, LUA_DIRSEP "\n" LUA_PATH_SEP "\n" LUA_PATH_MARK "\n"
                     LUA_EXEC_DIR "\n" LUA_IGMARK "\n");
  lua_setfield(L, -2, "config");
  /* set field 'loaded' */
  luaL_getsubtable(L, LUA_REGISTRYINDEX, LUA_LOADED_TABLE);
  lua_setfield(L, -2, "loaded");
  /* set field 'preload' */
  luaL_getsubtable(L, LUA_REGISTRYINDEX, LUA_PRELOAD_TABLE);
  lua_setfield(L, -2, "preload");
  lua_pushglobaltable(L);
  lua_pushvalue(L, -2);  /* set 'package' as upvalue for next lib */
  luaL_setfuncs(L, ll_funcs, 1);  /* open lib into global table */
  lua_pop(L, 1);  /* pop global table */
  return 1;  /* return 'package' table */
}
```

--------------------------------

### Get function definition line using lua_getinfo

Source: https://www.lua.org/manual/5.5/manual.html

Example showing how to retrieve the line number where a global function 'f' is defined.

```c
     lua_Debug ar;
     lua_getglobal(L, "f");  /* get global 'f' */
     lua_getinfo(L, ">S", &ar);
     printf("%d\n", ar.linedefined);
```

--------------------------------

### Main Program Thread Initialization

Source: https://www.lua.org/pil/9.4.html

Example of creating threads to download multiple documents and invoking the dispatcher.

```lua
    host = "www.w3.org"
    
    get(host, "/TR/html401/html40.txt")
    get(host,"/TR/2002/REC-xhtml1-20020801/xhtml1.pdf")
    get(host,"/TR/REC-html32.html")
    get(host,
        "/TR/2000/REC-DOM-Level-2-Core-20001113/DOM2-Core.txt")
    
    dispatcher()   -- main loop
```

--------------------------------

### Lua example: arithmetic expression bug with many variables

Source: https://www.lua.org/bugs.html

Reproduces wrong code generation for arithmetic expressions when using almost 256 names. The example assigns many variables and prints the same expression twice, expecting '2 2' but getting '1 2' on the second print.

```lua
-- use a large number of names (almost 256)
v1=1; v2=1; v3=1; v4=1; v5=1; v6=1; v7=1; v8=1; v9=1;
v10=1; v11=1; v12=1; v13=1; v14=1; v15=1; v16=1; v17=1;
v18=1; v19=1; v20=1; v21=1; v22=1; v23=1; v24=1; v25=1;
v26=1; v27=1; v28=1; v29=1; v30=1; v31=1; v32=1; v33=1;
v34=1; v35=1; v36=1; v37=1; v38=1; v39=1; v40=1; v41=1;
v42=1; v43=1; v44=1; v45=1; v46=1; v47=1; v48=1; v49=1;
v50=1; v51=1; v52=1; v53=1; v54=1; v55=1; v56=1; v57=1;
v58=1; v59=1; v60=1; v61=1; v62=1; v63=1; v64=1; v65=1;
v66=1; v67=1; v68=1; v69=1; v70=1; v71=1; v72=1; v73=1;
v74=1; v75=1; v76=1; v77=1; v78=1; v79=1; v80=1; v81=1;
v82=1; v83=1; v84=1; v85=1; v86=1; v87=1; v88=1; v89=1;
v90=1; v91=1; v92=1; v93=1; v94=1; v95=1; v96=1; v97=1;
v98=1; v99=1; v100=1; v101=1; v102=1; v103=1; v104=1; v105=1;
v106=1; v107=1; v108=1; v109=1; v110=1; v111=1; v112=1; v113=1;
v114=1; v115=1; v116=1; v117=1; v118=1; v119=1; v120=1; v121=1;
v122=1; v123=1; v124=1; v125=1; v126=1; v127=1; v128=1; v129=1;
v130=1; v131=1; v132=1; v133=1; v134=1; v135=1; v136=1; v137=1;
v138=1; v139=1; v140=1; v141=1; v142=1; v143=1; v144=1; v145=1;
v146=1; v147=1; v148=1; v149=1; v150=1; v151=1; v152=1; v153=1;
v154=1; v155=1; v156=1; v157=1; v158=1; v159=1; v160=1; v161=1;
v162=1; v163=1; v164=1; v165=1; v166=1; v167=1; v168=1; v169=1;
v170=1; v171=1; v172=1; v173=1; v174=1; v175=1; v176=1; v177=1;
v178=1; v179=1; v180=1; v181=1; v182=1; v183=1; v184=1; v185=1;
v186=1; v187=1; v188=1; v189=1; v190=1; v191=1; v192=1; v193=1;
v194=1; v195=1; v196=1; v197=1; v198=1; v199=1; v200=1; v201=1;
v202=1; v203=1; v204=1; v205=1; v206=1; v207=1; v208=1; v209=1;
v210=1; v211=1; v212=1; v213=1; v214=1; v215=1; v216=1; v217=1;
v218=1; v219=1; v220=1; v221=1; v222=1; v223=1; v224=1; v225=1;
v226=1; v227=1; v228=1; v229=1; v230=1; v231=1; v232=1; v233=1;
v234=1; v235=1; v236=1; v237=1; v238=1; v239=1; v240=1; v241=1;
v242=1; v243=1; v244=1; v245=1; v246=1; v247=1; v248=1; v249=1;
v250=1;
v251={k1 = 1};
v252=1;
print(2 * v251.k1, v251.k1 * 2);   -- 2 2, OK
v253=1;
print(2 * v251.k1, v251.k1 * 2);   -- 1 2, ???
```

--------------------------------

### Check if string is an integer with optional sign using string.find and pattern ^[+-]?%d+$

Source: https://www.lua.org/pil/20.2.html

This example uses both ^ and $ anchors to test if the entire string s is an integer with an optional sign. The pattern ^[+-]?%d+$ matches a sign, followed by one or more digits, from start to end.

```lua
    if string.find(s, "^[+-]?%d+$") then ...

```

--------------------------------

### luaopen_os entry point

Source: https://www.lua.org/source/5.5/loslib.c.html

The library initialization function that registers the OS library.

```c
LUAMOD_API int luaopen_os (lua_State *L) {
  luaL_newlib(L, syslib);
  return 1;
}
```

--------------------------------

### Create a proxy table to track accesses

Source: https://www.lua.org/pil/13.4.4.html

This example demonstrates creating an empty proxy table with __index and __newindex metamethods to monitor all read and write operations on an original table t.

```lua
    t = {}   -- original table (created somewhere)
    
    -- keep a private access to original table
    local _t = t
    
    -- create proxy
    t = {}
    
    -- create metatable
    local mt = {
      __index = function (t,k)
        print("*access to element " .. tostring(k))
        return _t[k]   -- access the original table
      end,
    
      __newindex = function (t,k,v)
        print("*update of element " .. tostring(k) ..
                             " to " .. tostring(v))
        _t[k] = v   -- update original table
      end
    }
    setmetatable(t, mt)
```

--------------------------------

### Multiple Assignment Example

Source: https://www.lua.org/pil/4.1.html

Example of assigning multiple variables to values.

```lua
    a, b, c = 0, 0, 0
    print(a,b,c)           --> 0   0   0
```

--------------------------------

### lua_setfenv crash example

Source: https://www.lua.org/bugs.html

Example of calling debug.setfenv on an invalid object.

```lua
> debug.setfenv(3, {})
```

--------------------------------

### Execute system commands with os.execute

Source: https://www.lua.org/pil/22.2.html

Shows how to use os.execute to run system commands, such as creating a directory.

```lua
    function createDir (dirname)
      os.execute("mkdir " .. dirname)
    end

```

--------------------------------

### Lua Table Configuration Example

Source: https://www.lua.org/pil/25.1.html

An alternative configuration approach using a Lua table for the background color.

```lua
    background = {r=0.30, g=0.10, b=0}
```

--------------------------------

### Initialize a record-style table

Source: https://www.lua.org/pil/3.6.html

Two equivalent ways to initialize a table as a record.

```lua
    a = {x=0, y=0}
```

```lua
    a = {}; a.x=0; a.y=0
```

--------------------------------

### Numeric for loop examples

Source: https://www.lua.org/pil/4.3.4.html

Examples of a standard incrementing loop and a decrementing loop.

```lua
    for i=1,f(x) do print(i) end
    
    for i=10,1,-1 do print(i) end
```

--------------------------------

### CSV data example

Source: https://www.lua.org/pil/20.4.html

An example array of strings to be converted into CSV format.

```lua
    {'a b', 'a,b', ' a,"b"c', 'hello "world"!', ''}
```

--------------------------------

### Create a list using table syntax

Source: https://www.lua.org/spe.html

Demonstrates the shorthand syntax for creating a list of values.

```lua
      colors = {"blue", "yellow", "red", "green", "black"}
```

--------------------------------

### Quick-and-dirty execution with loadstring

Source: https://www.lua.org/pil/8.html

Shows how to load and run a chunk in one line, and how to use assert to handle potential errors.

```lua
    loadstring(s)()
```

```lua
    assert(loadstring(s))()
```

--------------------------------

### Non-Tail Call Examples

Source: https://www.lua.org/manual/5.5/manual.html

Examples of function calls that do not qualify as tail calls.

```lua
     return (f(x))        -- results adjusted to 1
     return 2 * f(x)      -- result multiplied by 2
     return x, f(x)       -- additional results
     f(x); return         -- results discarded
     return x or f(x)     -- results adjusted to 1
```

--------------------------------

### Example weave source configuration

Source: https://www.lua.org/notes/ltn010a.html

A sample configuration snippet for a weave source file.

```lua
-- Technote source for weave
--  GCW August 2001

-- Please set value of filename for your own computer
filename = "ltn010.html"
```

--------------------------------

### Initialize an array with a loop

Source: https://www.lua.org/pil/11.1.html

Demonstrates creating a new table and populating it with 1000 elements using a for loop.

```lua
    a = {}    -- new array
    for i=1, 1000 do
      a[i] = 0
    end
```

--------------------------------

### Starting the Maze Game

Source: https://www.lua.org/pil/6.3.html

The initial call to start the maze state machine.

```lua
    room1()
```

--------------------------------

### Initialize a table with fields

Source: https://www.lua.org/spe.html

Creates a table and initializes its fields x, y, and foreground.

```lua
      window1 = {x = 200, y = 300, foreground = "blue"}
```

--------------------------------

### Expat XML tag example

Source: https://www.lua.org/pil/29.2.html

An example of an XML tag string processed by the parser.

```xml
    <tag cap="5">hi</tag>
```

--------------------------------

### luaopen_math initialization

Source: https://www.lua.org/source/5.5/lmathlib.c.html

Opens the math library and registers constants and functions.

```c
LUAMOD_API int luaopen_math (lua_State *L) {
  luaL_newlib(L, mathlib);
  lua_pushnumber(L, PI);
  lua_setfield(L, -2, "pi");
  lua_pushnumber(L, (lua_Number)HUGE_VAL);
  lua_setfield(L, -2, "huge");
  lua_pushinteger(L, LUA_MAXINTEGER);
  lua_setfield(L, -2, "maxinteger");
  lua_pushinteger(L, LUA_MININTEGER);
  lua_setfield(L, -2, "mininteger");
  setrandfunc(L);
  return 1;
}
```

--------------------------------

### Example Profiler Output

Source: https://www.lua.org/pil/23.3.html

Sample output generated by applying the profiler to the markov example.

```text
    [markov.lua]:4 884723
    write   10000
    [markov.lua]:0 (f)     1
    read    31103
    sub     884722
    [markov.lua]:1 (allwords)      1
    [markov.lua]:20 (prefix)       894723
    find    915824
    [markov.lua]:26 (insert)       884723
    random  10000
    sethook 1
    insert  884723
```

--------------------------------

### UI Component Creation

Source: https://www.lua.org/ddj.html

Examples of creating buttons, top-level windows, and message dialogs with nested layouts.

```lua
(a)
     b = button{label = "Hello world!"
                command = "exit(0)"
               }


(b)
     w = toplevel{b}
     w:show()

(c)
     b1 = button{label="Yes", command="yes=1"}
     b2 = button{label="No", command="yes=0"}
     w  = toplevel{message{text="Overwrite file?"},
                   frame{b1, b2; side="left"};
                   side="top"
                  }
```

--------------------------------

### Arithmetic expression input example

Source: https://www.lua.org/spe.html

An example of an arithmetic expression string that can be processed by the expression parser.

```text
      (a*a+b*b)*(a*a-b*b)/(a*a+b*b+c)+(a*(b*b)*c)
```

--------------------------------

### Example call_va usage

Source: https://www.lua.org/pil/25.3.html

An example of how to invoke the call_va wrapper function with a signature string and arguments.

```c
    call_va("f", "dd>d", x, y, &z);
```

--------------------------------

### Compiler option for static configuration

Source: https://www.lua.org/pil/26.2.html

Example command-line compiler flag to include the custom configuration header.

```bash
    -DLUA_USERCONFIG="mylib.h"
```

--------------------------------

### Create a list by manual assignment

Source: https://www.lua.org/semish94.html

Initializes an empty table and populates it with list elements.

```lua
        t = @()
        t[1] = "red"
        t[2] = "green"
        t[3] = "blue"
        t[4] = 3
```

--------------------------------

### AS400 Buffer Overflow Example

Source: https://www.lua.org/bugs.html

Example triggering potential buffer overflow on AS400 machines.

```lua
print{}  -- on an AS400 machine
```

--------------------------------

### Global State Initialization

Source: https://www.lua.org/work/diffu-lua-5.4.2-lua-5.4.3.txt

Added gcstopem initialization to global_State.

```c
   g->panic = NULL;
   g->gcstate = GCSpause;
   g->gckind = KGC_INC;
+  g->gcstopem = 0;
   g->gcemergency = 0;
```

--------------------------------

### Simple Lua configuration file

Source: https://www.lua.org/pil/25.html

A basic Lua script defining global variables for window dimensions.

```lua
-- configuration file for program `pp'
-- define window size
width = 200
height = 300
```

--------------------------------

### debug.sethook stack overflow example

Source: https://www.lua.org/bugs.html

Example showing how debug.sethook can overflow a thread's stack.

```lua
a = coroutine.create(function() yield() end)
coroutine.resume(a)
debug.sethook(a)      -- may overflow the stack of 'a'
```
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