Add tons of builtin helpers and array operations.

object/builtin_lower.go

@@ -0,0 +1,16 @@
+package object
+
+import "strings"
+
+// Lower ...
+func Lower(args ...Object) Object {
+	if len(args) != 1 {
+		return newError("wrong number of arguments. got=%d, want=1",
+			len(args))
+	}
+
+	if str, ok := args[0].(*String); ok {
+		return &String{Value: strings.ToLower(str.Value)}
+	}
+	return newError("expected `str` argument to `lower` got=%T", args[0])
+}