Add helper function to easily create lua libraries (#116)

_example/library.go

@@ -0,0 +1,36 @@
+package main
+
+import "github.com/aarzilli/golua/lua"
+
+func test(L *lua.State) int {
+	println("hello!")
+	return 0
+}
+
+func test2(L *lua.State) int {
+	println("world!")
+	return 0
+}
+
+var funcs = map[string]lua.LuaGoFunction{
+	"test": test,
+	"test2": test2,
+}
+
+const code = `
+	local example = require("example")
+	example.test()
+	example.test2()
+	`
+
+func main() {
+	L := lua.NewState()
+	defer L.Close()
+	L.OpenLibs()
+
+	L.RegisterLibrary("example", funcs)
+
+	if err := L.DoString(code); err != nil {
+		panic(err)
+	}
+}

lua/lua.go

@@ -438,6 +438,29 @@ func (L *State) Register(name string, f LuaGoFunction) {
 	L.SetGlobal(name)
 }
 
+// Registers a map of go functions as a library that can be accessed using "require("name")"
+func (L *State) RegisterLibrary(name string, funcs map[string]LuaGoFunction) {
+	L.GetGlobal(name)
+	found := L.IsTable(-1)
+	if !found {
+		L.Pop(1)
+		L.CreateTable(0, len(funcs))
+	}
+
+	for fname, f := range funcs {
+		L.PushGoFunction(f)
+		L.SetField(-2, fname)
+	}
+
+	if !found {
+		L.GetGlobal("package")
+		L.GetField(-1, "loaded")
+		L.PushValue(-3)
+		L.SetField(-2, name)
+		L.Pop(2)
+	}
+}
+
 // lua_setallocf
 func (L *State) SetAllocf(f Alloc) {
 	L.allocfn = &f