restructure project

internal/builtins/first.go

@@ -0,0 +1,24 @@
+package builtins
+
+import (
+	"monkey/internal/object"
+	"monkey/internal/typing"
+)
+
+// First ...
+func First(args ...object.Object) object.Object {
+	if err := typing.Check(
+		"first", args,
+		typing.ExactArgs(1),
+		typing.WithTypes(object.ARRAY_OBJ),
+	); err != nil {
+		return newError(err.Error())
+	}
+
+	arr := args[0].(*object.Array)
+	if len(arr.Elements) > 0 {
+		return arr.Elements[0]
+	}
+
+	return nil
+}