feat: call function with one argument

builtin/function.go

@@ -1,11 +1,26 @@
 package builtin
 
-import "time"
+import (
+	"math/rand"
+	"time"
+)
 
 var Functions = map[string]interface{}{
-	"sleep": Sleep,
+	"sleep":             sleep,
+	"gen_random_string": genRandomString,
 }
 
-func Sleep(nSecs int) {
+func sleep(nSecs int) {
 	time.Sleep(time.Duration(nSecs) * time.Second)
 }
+
+func genRandomString(n int) string {
+	const letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890"
+	const lettersLen = len(letters)
+
+	b := make([]byte, n)
+	for i := range b {
+		b[i] = letters[rand.Intn(lettersLen)]
+	}
+	return string(b)
+}