Add example with lua built-in function

Makefile

@@ -12,6 +12,7 @@ WINDOWS_BINARY1=${MYNAME1}.exe
 WINDOWS_BINARY2=${MYNAME2}.exe
 EXAMPLE01=01-LoadJsonFile
 EXAMPLE02=02-TestLuaScript
+EXAMPLE03=03-UseGoFuncInLua
 
 RMCMD=rm -rf
 
@@ -71,29 +72,34 @@ clean:
 ifeq ($(OS),Windows_NT)
 ifeq ($(SHELL),sh.exe)
 #	# Vanilla cmd.exe / powershell.
-	if exist 01-LoadJsonFile.exe ${RMCMD} ${WINDOWS_BINARY1}
+	if exist ${WINDOWS_BINARY1} ${RMCMD} ${WINDOWS_BINARY1}
-	if exist 01-LoadJsonFile.exe ${RMCMD} ${UNIX_BINARY1}
+	if exist ${UNIX_BINARY1} ${RMCMD} ${UNIX_BINARY1}
-	if exist 01-LoadJsonFile.exe ${RMCMD} ${WINDOWS_BINARY2}
+	if exist ${WINDOWS_BINARY2} ${RMCMD} ${WINDOWS_BINARY2}
-	if exist 01-LoadJsonFile.exe ${RMCMD} ${UNIX_BINARY2}
+	if exist ${UNIX_BINARY2} ${RMCMD} ${UNIX_BINARY2}
-	if exist 01-LoadJsonFile.exe ${RMCMD} 01-LoadJsonFile.exe
+	if exist ${EXAMPLE01}.exe ${RMCMD} ${EXAMPLE01}.exe
-	if exist 01-LoadJsonFile ${RMCMD} 01-LoadJsonFile
+	if exist ${EXAMPLE01} ${RMCMD} ${EXAMPLE01}
-	if exist 02-TestLuaScript.exe ${RMCMD} 02-TestLuaScript.exe
+	if exist ${EXAMPLE02}.exe ${RMCMD} ${EXAMPLE02}.exe
-	if exist 02-TestLuaScript ${RMCMD} 02-TestLuaScript
+	if exist ${EXAMPLE02} ${RMCMD} ${EXAMPLE02}
+	if exist ${EXAMPLE03}.exe ${RMCMD} ${EXAMPLE03}.exe
+	if exist ${EXAMPLE03} ${RMCMD} ${EXAMPLE03}
 else  # not ifeq ($(SHELL),sh.exe)
 	${RMCMD} ${WINDOWS_BINARY1}
 	${RMCMD} ${UNIX_BINARY1}
 	${RMCMD} ${WINDOWS_BINARY2}
 	${RMCMD} ${UNIX_BINARY2}
-	${RMCMD} ./01-LoadJsonFile.exe
+	${RMCMD} ${EXAMPLE01}.exe
-	${RMCMD} ./01-LoadJsonFile
+	${RMCMD} ${EXAMPLE01}
-	${RMCMD} ./02-TestLuaScript.exe
+	${RMCMD} ${EXAMPLE02}.exe
-	${RMCMD} ./02-TestLuaScript
+	${RMCMD} ${EXAMPLE02}
+	${RMCMD} ${EXAMPLE03}.exe
+	${RMCMD} ${EXAMPLE03}
 endif # ifeq ($(SHELL),sh.exe)
 else  # not ifeq ($(OS),Windows_NT)
 	${RMCMD} ${BINARY1}
 	${RMCMD} ${BINARY2}
-	${RMCMD} ./01-LoadJsonFile
+	${RMCMD} ${EXAMPLE01}
-	${RMCMD} ./02-TestLuaScript
+	${RMCMD} ${EXAMPLE02}
+	${RMCMD} ${EXAMPLE03}
 endif
 
 
@@ -103,7 +109,7 @@ upgrade:
 	go mod vendor
 
 
-01-LoadJsonFile: clean
+${EXAMPLE01}: clean
 ifeq ($(OS),Windows_NT)
 # Looks like on windows gnu make explicitly set SHELL to sh.exe, if it was not set.
 ifeq ($(SHELL), sh.exe)
@@ -123,7 +129,7 @@ else  # not  ($(OS),Windows_NT)
 endif # ifeq ($(OS),Windows_NT)
 
 
-02-TestLuaScript: clean
+${EXAMPLE02}: clean
 ifeq ($(OS),Windows_NT)
 # Looks like on windows gnu make explicitly set SHELL to sh.exe, if it was not set.
 ifeq ($(SHELL), sh.exe)
@@ -143,4 +149,24 @@ else  # not  ($(OS),Windows_NT)
 endif # ifeq ($(OS),Windows_NT)
 
 
+${EXAMPLE03}: clean
+ifeq ($(OS),Windows_NT)
+# Looks like on windows gnu make explicitly set SHELL to sh.exe, if it was not set.
+ifeq ($(SHELL), sh.exe)
+#       # Vanilla cmd.exe / powershell.
+	SET "CGO_ENABLED=0"
+	go build ${BUILDOPTS} -o ${EXAMPLE03}.exe ./examples/${EXAMPLE03}
+else ifeq (,$(findstring(Git/usr/bin/sh.exe, $(SHELL))))
+#       # git-bash
+	CGO_ENABLED=0 go build ${BUILDOPTS} -o ${EXAMPLE03}.exe ./examples/${EXAMPLE03}
+else  # not ifeq (,$(findstring(Git/usr/bin/sh.exe, $(SHELL))))
+#       # Some other shell.
+#       # TODO: handle it.
+	$(info "-- Dunno how to handle this shell: ${SHELL}")
+endif # ifeq (,$(findstring(Git/usr/bin/sh.exe, $(SHELL))))
+else  # not  ($(OS),Windows_NT)
+	CGO_ENABLED=0 go build ${BUILDOPTS} -o ${EXAMPLE03} ./examples/${EXAMPLE03}
+endif # ifeq ($(OS),Windows_NT)
+
+
 # vim: set ft=make noet ai ts=4 sw=4 sts=4:

example_data/02-test.lua

@@ -1,3 +1,3 @@
 print ("Hello World!")
 
--- vim: set ft=go noet ai ts=4 sw=4 sts=4:
+-- vim: set ft=lua noet ai ts=4 sw=4 sts=4:

example_data/03-test.lua

@@ -0,0 +1,3 @@
+print("4 * 4 = " .. square(4))
+
+-- vim: set ft=lua noet ai ts=4 sw=4 sts=4:

examples/02-TestLuaScript/main.go

@@ -8,11 +8,10 @@ import (
 )
 
 func main() {
-	file := "example_data/02-test.lua"
+	// Init log subsystem.
 	log.Init("info", os.Stderr)
 
-	L := lua.NewState()
+	file := "example_data/02-test.lua"
-	defer L.Close()
 
 	// Load the Lua script file.
 	log.Infof("Loading %s", file)
@@ -22,11 +21,14 @@ func main() {
 	luaCode, err := os.ReadFile(file)
 
 	if err != nil {
-		log.Errorf("Error reading Lua file %s: %s", file, err)
+		log.Fatalf("Error reading Lua file %s: %s", file, err)
-
-		os.Exit(1)
 	}
 
+	log.Info("Creating new Lua state")
+	L := lua.NewState()
+	defer L.Close()
+
+	log.Info("Evaluating Lua code")
 	if err := L.DoString(string(luaCode)); err != nil {
 		log.Errorf("Error evaluating Lua code: %s", err)
 

examples/03-UseGoFuncInLua/main.go

@@ -0,0 +1,59 @@
+package main
+
+// https://otm.github.io/2015/07/embedding-lua-in-go/
+
+import (
+	"doll/internal/log"
+	"os"
+
+	lua "github.com/yuin/gopher-lua"
+)
+
+// square multiplies number by itself.
+func square(L *lua.LState) int {
+	// get first (1) function argument and convert to int
+	i := L.ToInt(1)
+
+	// make calculation and cast to LNumber
+	ln := lua.LNumber(i * i)
+
+	// Push it to the stack
+	L.Push(ln)
+
+	// Notify that we pushed one value to the stack
+	return 1
+}
+
+func main() {
+	// Init log subsystem.
+	log.Init("info", os.Stderr)
+
+	file := "example_data/03-test.lua"
+
+	// Load the Lua script file.
+	log.Infof("Loading %s", file)
+
+	// We can execute script directly via L.DoFile("./example_data/03-test.lua") but in practice we'll get scripts as
+	// strings - snippets from templates - so, testing/checking how it works is not use for project.
+	luaCode, err := os.ReadFile(file)
+
+	if err != nil {
+		log.Fatalf("Error reading Lua file %s: %s", file, err)
+	}
+
+	log.Info("Creating new Lua state")
+	L := lua.NewState()
+	defer L.Close()
+
+	log.Info("Registering go function as lua built-in function")
+	L.SetGlobal("square", L.NewFunction(square))
+
+	log.Info("Evaluating Lua code")
+	if err := L.DoString(string(luaCode)); err != nil {
+		log.Errorf("Error evaluating Lua code: %s", err)
+
+		os.Exit(1)
+	}
+}
+
+/* vim: set ft=go noet ai ts=4 sw=4 sts=4: */