From 80a72b616be214a2da064589fc6aeffaf2cca879 Mon Sep 17 00:00:00 2001
From: Pekka Laiho <pekka.i.laiho@gmail.com>
Date: Sun, 18 Oct 2020 09:30:21 +0700
Subject: [PATCH] support strings for empty?

---
 README.md               |  1 +
 src/Lib/Collections.php | 10 +++++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 687f4cb..ce3318a 100644
--- a/README.md
+++ b/README.md
@@ -271,6 +271,7 @@ sqrt  | `(sqrt 2)` | `1.41` | Calculate the square root.
 
 Name    | Example | Example result | Description
 ------- | ------- | -------------- | -----------
+empty?  | `(empty? "")` | `true` | Return true if argument is empty string.
 len     | `(len "hello world")` | `11` | Return the length of a string using [strlen](https://www.php.net/manual/en/function.strlen.php).
 trim    | `(trim " abc ")` | `"abc"` | Trim the string using [trim](https://www.php.net/manual/en/function.trim).
 upcase  | `(upcase "abc")` | `"ABC"` | Make the string upper case using [strtoupper](https://www.php.net/manual/en/function.strtoupper).
diff --git a/src/Lib/Collections.php b/src/Lib/Collections.php
index 45089b1..a2e0d7e 100644
--- a/src/Lib/Collections.php
+++ b/src/Lib/Collections.php
@@ -45,7 +45,15 @@ class Collections implements ILib
         // Read information
 
         $env->set('empty?', new CoreFunc('empty?', 'Return true if collection is empty.', 1, 1,
-            fn (Collection $a) => $a->count() == 0
+            function ($a) {
+                if ($a instanceof Collection) {
+                    return $a->count() === 0;
+                } elseif (is_string($a)) {
+                    return $a === '';
+                }
+
+                throw new MadLispException('argument to empty? is not collection or string');
+            }
         ));
 
         $env->set('get', new CoreFunc('get', 'Get the item from first argument (collection) by using the second argument as index or key.', 2, 2,