restructure project

internal/builtins/join.go

@@ -0,0 +1,26 @@
+package builtins
+
+import (
+	"monkey/internal/object"
+	"monkey/internal/typing"
+	"strings"
+)
+
+// Join ...
+func Join(args ...object.Object) object.Object {
+	if err := typing.Check(
+		"join", args,
+		typing.ExactArgs(2),
+		typing.WithTypes(object.ARRAY_OBJ, object.STRING_OBJ),
+	); err != nil {
+		return newError(err.Error())
+	}
+
+	arr := args[0].(*object.Array)
+	sep := args[1].(*object.String)
+	a := make([]string, len(arr.Elements))
+	for i, el := range arr.Elements {
+		a[i] = el.String()
+	}
+	return &object.String{Value: strings.Join(a, sep.Value)}
+}