Basic building blocks to interface Haskell and Lua in a Haskell-idiomatic style.
Lua is a small, well-designed, embeddable scripting language. It has become the de-facto default to make programs extensible and is widely used everywhere from servers over games and desktop applications up to security software and embedded devices. This package provides the basic building blocks for coders to embed Lua into their programs.
This package is part of HsLua, a Haskell framework built around the embeddable scripting language Lua.
Interacting with Lua
HsLua core provides the
Lua type to define Lua operations. The
operations are executed by calling
run. A simple “Hello, World”
program, using the Lua
import HsLua.Core.Lua as Lua main :: IO () main = Lua.run prog where prog :: Lua () prog = do Lua.openlibs -- load Lua libraries so we can use 'print' Lua.getglobal "print" -- push print function Lua.pushstring "Hello, World!" -- push string argument Lua.call (NumArgs 1) -- number of arguments passed to the function (NumResults 0) -- number of results expected -- as return values
The Lua stack
Lua’s API is stack-centered: most operations involve pushing
values to the stack or receiving items from the stack. E.g.,
calling a function is performed by pushing the function onto the
stack, followed by the function arguments in the order they should
be passed to the function. The API function
call then invokes
the function with given numbers of arguments, pops the function
and parameters off the stack, and pushes the results.
,----------. | arg 3 | +----------+ | arg 2 | +----------+ | arg 1 | +----------+ ,----------. | function | call 3 1 | result 1 | +----------+ ===========> +----------+ | | | | | stack | | stack | | | | |
This package provides all basic building blocks to interact with
the Lua stack. If you’d like more comfort, please consider using
Errors and exceptions must always be caught and converted when
passing language boundaries. The exception type which can be
handled is encoded as the type
e in the monad
LuaE e. Only
exceptions of this type may be thrown; throwing different
exceptions across language boundaries will lead to a program
Exceptions must support certain operations as defined by the
LuaError typeclass. The class ensures that errors can be
converted from and to Lua values, and that a new exception can be
created from a String message.