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GHC 9.10.3 · lts/ghc-9.10.x · c74966e · 2026-09-27

Modulelua-2.3.2Haskell2010

Lua.Primary

Haskell bindings to Lua C API functions.

The exposed functions correspond closely to the respective C Lua API functions. However, C API functions which can throw Lua errors are not exported directly, as any errors would crash the program. Non-error throwing hslua_ versions are provided instead. The hslua ersatz functions have worse performance than the original.

Some of the Lua functions may, directly or indirectly, call a Haskell function, and trigger garbage collection, rescheduling etc. These functions are always imported safely (i.e., with the safe keyword).

However, all function can trigger garbage collection. If that can lead to problems, then the package should be configured without flag allow-unsafe-gc.

  • 75 values
  • Packagelua-2.3.2
  • Exports75
  • LanguageHaskell2010
  • LicenceMIT
  • SourcePrimary.hs
valuelua_arith
  1. :: State
  2. -> ArithOPCode

    op

  3. -> IO ()
#

This is an unsafe function, errors will lead to a program crash; consider using hslua_arith instead.

Performs an arithmetic or bitwise operation over the two values (or one, in the case of negations) at the top of the stack, with the value at the top being the second operand, pops these values, and pushes the result of the operation. The function follows the semantics of the corresponding Lua operator (that is, it may call metamethods).

The value of op must be one of the following constants:

  • LUA_OPADD: performs addition (+)

  • LUA_OPSUB: performs subtraction (-)

  • LUA_OPMUL: performs multiplication (*)

  • LUA_OPDIV: performs float division (/)

  • LUA_OPIDIV: performs floor division (//)

  • LUA_OPMOD: performs modulo (%)

  • LUA_OPPOW: performs exponentiation (^)

  • LUA_OPUNM: performs mathematical negation (unary -)

  • LUA_OPBNOT: performs bitwise NOT (~)

  • LUA_OPBAND: performs bitwise AND (&)

  • LUA_OPBOR: performs bitwise OR (|)

  • LUA_OPBXOR: performs bitwise exclusive OR (~)

  • LUA_OPSHL: performs left shift (<<)

  • LUA_OPSHR: performs right shift (>>)

WARNING: lua_arith is unsafe in Haskell: if the call to a metamethod triggers an error, then that error cannot be handled and will lead to an unrecoverable program crash. Consider using the Lua.hslua_arith ersatz function instead. Likewise, the metamethod may not call a Haskell function unless the library was compiled without allow-unsafe-gc.

https://www.lua.org/manual/5.4/manual.html#lua_arith.

valuelua_checkstack
  1. :: State
  2. -> CInt

    n

  3. -> IO LuaBool
#

Ensures that the stack has space for at least n extra slots (that is, that you can safely push up to n values into it). It returns false if it cannot fulfill the request, either because it would cause the stack to be larger than a fixed maximum size (typically at least several thousand elements) or because it cannot allocate memory for the extra space. This function never shrinks the stack; if the stack already has space for the extra slots, it is left unchanged.

https://www.lua.org/manual/5.4/manual.html#lua_checkstack

valuelua_close :: State -> IO ()
#

Destroys all objects in the given Lua state (calling the corresponding garbage-collection metamethods, if any) and frees all dynamic memory used by this state. In several platforms, you may not need to call this function, because all resources are naturally released when the host program ends. On the other hand, long-running programs that create multiple states, such as daemons or web servers, will probably need to close states as soon as they are not needed.

https://www.lua.org/manual/5.4/manual.html#lua_close

valuelua_concat
  1. :: State
  2. -> CInt

    n

  3. -> IO ()
#

This is an unsafe function, it will cause a program crash if a metamethod throws an error. Consider using hslua_concat instead.

Concatenates the n values at the top of the stack, pops them, and leaves the result at the top. If n is 1, the result is the single value on the stack (that is, the function does nothing); if n is 0, the result is the empty string. Concatenation is performed following the usual semantics of Lua (see §3.4.6 of the Lua manual).

WARNING: lua_concat is unsafe in Haskell: This function will cause an unrecoverable crash an error if any of the concatenated values causes an error when executing a metamethod. Consider using the Lua.hslua_concat ersatz function instead.

valuelua_createtable
  1. :: State
  2. -> CInt

    narr

  3. -> CInt

    nrec

  4. -> IO ()
#

Creates a new empty table and pushes it onto the stack. Parameter narr is a hint for how many elements the table will have as a sequence; parameter nrec is a hint for how many other elements the table will have. Lua may use these hints to preallocate memory for the new table. This preallocation is useful for performance when you know in advance how many elements the table will have. Otherwise you can use the function lua_newtable.

https://www.lua.org/manual/5.4/manual.html#lua_createtable.

valuelua_getglobal
  1. :: State
  2. -> CString

    name

  3. -> IO TypeCode
#

This is an unsafe function, errors will lead to a program crash; consider using hslua_getglobal instead.

Pushes onto the stack the value of the global name. Returns the type of that value.

WARNING: lua_getglobal is unsafe in Haskell: if the call to a metamethod triggers an error, then that error cannot be handled and will lead to an unrecoverable program crash. Consider using the Lua.hslua_getglobal ersatz function instead. Likewise, the metamethod may not call a Haskell function unless the library was compiled without allow-unsafe-gc.

https://www.lua.org/manual/5.4/manual.html#lua_getglobal.

valuelua_gettable
  1. :: State
  2. -> StackIndex

    index

  3. -> IO TypeCode
#

This is an unsafe function, errors will lead to a program crash; consider using hslua_gettable instead.

Pushes onto the stack the value t[k], where t is the value at the given index and k is the value at the top of the stack.

This function pops the key from the stack, pushing the resulting value in its place. As in Lua, this function may trigger a metamethod for the "index" event (see §2.4).

Returns the type of the pushed value.

WARNING: lua_gettable is unsafe in Haskell: if the call to a metamethod triggers an error, then that error cannot be handled and will lead to an unrecoverable program crash. Consider using the Lua.hslua_gettable ersatz function instead. Likewise, the metamethod may not call a Haskell function unless the library was compiled without allow-unsafe-gc.

https://www.lua.org/manual/5.4/manual.html#lua_gettable.

valuelua_load
  1. :: State
  2. -> Reader

    reader

  3. -> Ptr ()

    data

  4. -> CString

    chunkname

  5. -> CString

    mode

  6. -> IO StatusCode
#

Loads a Lua chunk (without running it). If there are no errors, lua_load pushes the compiled chunk as a Lua function on top of the stack. Otherwise, it pushes an error message.

The return values of lua_load are:

  • Lua.LUA_OK: no errors;

  • Lua.LUA_ERRSYNTAX: syntax error during pre-compilation;

  • Lua.LUA_ERRMEM: memory allocation error;

  • Lua.LUA_ERRGCMM: error while running a __gc metamethod. (This error has no relation with the chunk being loaded. It is generated by the garbage collector.)

This function only loads a chunk; it does not run it.

lua_load automatically detects whether the chunk is text or binary, and loads it accordingly (see program luac).

The lua_load function uses a user-supplied reader function to read the chunk (see Reader). The data argument is an opaque value passed to the reader function.

The chunkname argument gives a name to the chunk, which is used for error messages and in debug information (see §4.7).

lua_load automatically detects whether the chunk is text or binary and loads it accordingly (see program luac). The string mode works as in function load, with the addition that a NULL value is equivalent to the string "bt".

lua_load uses the stack internally, so the reader function must always leave the stack unmodified when returning.

https://www.lua.org/manual/5.4/manual.html#lua_load.

valuelua_newthread :: State -> IO State
#

Creates a new thread, pushes it on the stack, and returns a State that represents this new thread. The new thread returned by this function shares with the original thread its global environment, but has an independent execution stack.

There is no explicit function to close or to destroy a thread. Threads are subject to garbage collection, like any Lua object.

https://www.lua.org/manual/5.4/manual.html#lua_newthread

valuelua_newuserdatauv
  1. :: State
  2. -> CSize

    size

  3. -> CInt

    nuvalue

  4. -> IO (Ptr ())
#

This function creates and pushes on the stack a new full userdata, with nuvalue associated Lua values, called user values, plus an associated block of raw memory with size bytes. (The user values can be set and read with the functions lua_setiuservalue and lua_getiuservalue.)

The function returns the address of the block of memory. Lua ensures that this address is valid as long as the corresponding userdata is alive (see §2.5). Moreover, if the userdata is marked for finalization (see §2.5.3), its address is valid at least until the call to its finalizer.

https://www.lua.org/manual/5.4/manual.html#lua_newuserdatauv.

valuelua_next
  1. :: State
  2. -> StackIndex

    index

  3. -> IO LuaBool
#

This is an unsafe function, it will cause a program crash if the given key is neither nil nor present in the table. Consider using hslua_next instead.

Pops a key from the stack, and pushes a key–value pair from the table at the given index (the "next" pair after the given key). If there are no more elements in the table, then lua_next returns Lua.FALSE (and pushes nothing).

A typical traversal looks like this:

-- table is in the stack at index 't'
lua_pushnil l    -- first key
let loop = lua_next l t >>= \case
      FALSE -> return ()
      _ -> do
        lua_type l (-2) >>= lua_typename l >>= peekCString >>= putStrLn
        lua_type l (-1) >>= lua_typename l >>= peekCString >>= putStrLn
        -- removes 'value'; keeps 'key' for next iteration
        lua_pop l 1
        loop
loop

While traversing a table, do not call lua_tolstring directly on a key, unless you know that the key is actually a string. Recall that lua_tolstring may change the value at the given index; this confuses the next call to lua_next.

See function next for the caveats of modifying the table during its traversal.

WARNING: lua_next is unsafe in Haskell: This function will cause an unrecoverable crash an error if the given key is neither nil nor present in the table. Consider using the Lua.hslua_next ersatz function instead.

valuelua_pcall
  1. :: State
  2. -> NumArgs

    nargs

  3. -> NumResults

    nresults

  4. -> StackIndex

    msgh

  5. -> IO StatusCode
#

Calls a function in protected mode.

To call a function you must use the following protocol: first, the function to be called is pushed onto the stack; then, the arguments to the function are pushed in direct order; that is, the first argument is pushed first. Finally you call lua_pcall; nargs is the number of arguments that you pushed onto the stack. All arguments and the function value are popped from the stack when the function is called. The function results are pushed onto the stack when the function returns. The number of results is adjusted to nresults, unless nresults is Lua.LUA_MULTRET. In this case, all results from the function are pushed. Lua takes care that the returned values fit into the stack space. The function results are pushed onto the stack in direct order (the first result is pushed first), so that after the call the last result is on the top of the stack.

If there is any error, lua_pcall catches it, pushes a single value on the stack (the error message), and returns the error code. lua_pcall always removes the function and its arguments from the stack.

If msgh is 0, then the error object returned on the stack is exactly the original error object. Otherwise, msgh is the location of a message handler. (This index cannot be a pseudo-index.) In case of runtime errors, this function will be called with the error object and its return value will be the object returned on the stack by lua_pcall.

Typically, the message handler is used to add more debug information to the error object, such as a stack traceback. Such information cannot be gathered after the return of lua_pcall, since by then the stack has unwound.

https://www.lua.org/manual/5.4/manual.html#lua_pcall.

valuelua_pushcclosure
  1. :: State
  2. -> CFunction

    fn

  3. -> NumArgs

    n

  4. -> IO ()
#

Pushes a new C closure onto the stack.

When a C function is created, it is possible to associate some values with it, thus creating a C closure (see §3.4); these values are then accessible to the function whenever it is called. To associate values with a C function, first these values should be pushed onto the stack (when there are multiple values, the first value is pushed first). Then lua_pushcclosure is called to create and push the C function onto the stack, with the argument n telling how many values should be associated with the function. lua_pushcclosure also pops these values from the stack.

The maximum value for n is 255.

https://www.lua.org/manual/5.4/manual.html#lua_pushcclosure.

valuelua_pushlightuserdata :: State -> Ptr a -> IO ()
#

Pushes a light userdata onto the stack.

Userdata represent C values in Lua. A light userdata represents a pointer, a Ptr () (i.e., void* in C lingo). It is a value (like a number): you do not create it, it has no individual metatable, and it is not collected (as it was never created). A light userdata is equal to "any" light userdata with the same C address.

https://www.lua.org/manual/5.4/manual.html#lua_pushlightuserdata.

valuelua_pushstring
  1. :: State
  2. -> CString

    s

  3. -> IO CString
#

Pushes the zero-terminated string pointed to by s onto the stack. Lua makes (or reuses) an internal copy of the given string, so the memory at s can be freed or reused immediately after the function returns.

Returns a pointer to the internal copy of the string.

If s is NULL, pushes nil and returns NULL.

valuelua_rotate
  1. :: State
  2. -> StackIndex

    idx

  3. -> CInt

    n

  4. -> IO ()
#

Rotates the stack elements between the valid index idx and the top of the stack. The elements are rotated n positions in the direction of the top, for a positive n, or -n positions in the direction of the bottom, for a negative n. The absolute value of n must not be greater than the size of the slice being rotated. This function cannot be called with a pseudo-index, because a pseudo-index is not an actual stack position.

https://www.lua.org/manual/5.4/manual.html#lua_rotate

valuelua_setglobal
  1. :: State
  2. -> CString

    name

  3. -> IO ()
#

This is an unsafe function, errors will lead to a program crash; consider using hslua_getglobal instead.

Pops a value from the stack and sets it as the new value of global name.

WARNING: lua_setglobal is unsafe in Haskell: if the call to a metamethod triggers an error, then that error cannot be handled and will lead to an unrecoverable program crash. Consider using the Lua.hslua_setglobal ersatz function instead. Likewise, the global metamethod may not call a Haskell function unless the library was compiled without allow-unsafe-gc.

https://www.lua.org/manual/5.4/manual.html#lua_setglobal.

valuelua_settable
  1. :: State
  2. -> StackIndex

    index

  3. -> IO ()
#

This is an unsafe function, errors will lead to a program crash; consider using hslua_settable instead.

Does the equivalent to t[k] = v, where t is the value at the given index, v is the value at the top of the stack, and k is the value just below the top.

This function pops both the key and the value from the stack. As in Lua, this function may trigger a metamethod for the "newindex" event (see §2.4).

WARNING: lua_settable is unsafe in Haskell: if the call to a metamethod triggers an error, then that error cannot be handled and will lead to an unrecoverable program crash. Consider using the Lua.hslua_settable ersatz function instead. Likewise, the metamethod may not call a Haskell function unless the library was compiled without allow-unsafe-gc.

https://www.lua.org/manual/5.4/manual.html#lua_settable

valuelua_status :: State -> IO StatusCode
#

Returns the status of this Lua thread.

The status can be Lua.LUA_OK for a normal thread, an error value if the thread finished the execution of a lua_resume with an error, or Lua.LUA_YIELD if the thread is suspended.

You can only call functions in threads with status Lua.LUA_OK. You can resume threads with status Lua.LUA_OK (to start a new coroutine) or Lua.LUA_YIELD (to resume a coroutine).

https://www.lua.org/manual/5.4/manual.html#lua_status.

valuelua_stringtonumber :: State -> CString -> IO CSize
#

Converts the zero-terminated string s to a number, pushes that number into the stack, and returns the total size of the string, that is, its length plus one. The conversion can result in an integer or a float, according to the lexical conventions of Lua (see §3.1). The string may have leading and trailing spaces and a sign. If the string is not a valid numeral, returns 0 and pushes nothing. (Note that the result can be used as a boolean, true if the conversion succeeds.)

https://www.lua.org/manual/5.4/manual.html#lua_stringtonumber.

valuelua_tointegerx
  1. :: State
  2. -> StackIndex

    index

  3. -> Ptr LuaBool

    isnum

  4. -> IO Integer
#

Converts the Lua value at the given acceptable index to the signed integral type Integer. The Lua value must be an integer, a number, or a string convertible to an integer (see §3.4.3 of the Lua 5.4 Reference Manual); otherwise, lua_tointegerx returns 0.

If the number is not an integer, it is truncated in some non-specified way.

If isnum is not NULL, its referent is assigned a boolean value that indicates whether the operation succeeded.

https://www.lua.org/manual/5.4/manual.html#lua_tointegerx

valuelua_tolstring
  1. :: State
  2. -> StackIndex

    index

  3. -> Ptr CSize

    len

  4. -> IO (Ptr CChar)
#

Converts the Lua value at the given index to a C string. If len is not NULL, it sets the referent with the string length. The Lua value must be a string or a number; otherwise, the function returns NULL. If the value is a number, then lua_tolstring also changes the actual value in the stack to a string. (This change confuses lua_next when lua_tolstring is applied to keys during a table traversal.)

lua_tolstring returns a pointer to a string inside the Lua state. This string always has a zero ('0') after its last character (as in C), but can contain other zeros in its body.

Because Lua has garbage collection, there is no guarantee that the pointer returned by lua_tolstring will be valid after the corresponding Lua value is removed from the stack.

https://www.lua.org/manual/5.4/manual.html#lua_tolstring

module Lua.Ersatz.Functions

module Lua.Ersatz.Auxiliary