From 2d34af6aa9312894c0e6967d30a0714f8a95c47d Mon Sep 17 00:00:00 2001
From: Veit Heller <veit@veitheller.de>
Date: Wed, 20 Jan 2021 09:54:08 +0100
Subject: [PATCH] feat: make empty? an interface (#1139)

---
 core/Array.carp       | 1 +
 core/Interfaces.carp  | 2 ++
 core/Map.carp         | 6 ++++--
 core/StaticArray.carp | 1 +
 core/String.carp      | 1 +
 test/string.carp      | 2 +-
 6 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/core/Array.carp b/core/Array.carp
index 1057515a..821b9fc1 100644
--- a/core/Array.carp
+++ b/core/Array.carp
@@ -46,6 +46,7 @@ It will sum the previous sum with each new value, starting at `0`.")
   (doc empty? "checks whether the array `a` is empty.")
   (defn empty? [a]
     (= (Array.length a) 0))
+  (implements empty? Array.empty?)
 
   (doc any? "checks whether any of the elements in `a` match the function `f`.")
   (defn any? [f a]
diff --git a/core/Interfaces.carp b/core/Interfaces.carp
index bab10793..3a60a52e 100644
--- a/core/Interfaces.carp
+++ b/core/Interfaces.carp
@@ -67,3 +67,5 @@
 (definterface slice (Fn [&a Int Int] a))
 
 (definterface blit (Fn [a] a)) ; For types that can be freely memcopied -- exact name is up for discussion
+
+(definterface empty? (Fn [&a] Bool))
diff --git a/core/Map.carp b/core/Map.carp
index 9eca24c6..f829119e 100644
--- a/core/Map.carp
+++ b/core/Map.carp
@@ -288,7 +288,8 @@
 
   (doc empty? "Check whether the map m is empty.")
   (defn empty? [m]
-    (= @(len m) 0))
+    (= (Map.length m) 0))
+  (implements empty? Map.empty?)
 
   (doc remove "Remove the value under the key k from the map m.")
   (defn remove [m k]
@@ -520,7 +521,8 @@
 
   (doc empty? "Check whether the set s is empty.")
   (defn empty? [s]
-    (= (length s) 0))
+    (= (Set.length s) 0))
+  (implements empty? Set.empty?)
 
   (doc remove "Remove the value `v` from the set `s`.")
   (defn remove [s v]
diff --git a/core/StaticArray.carp b/core/StaticArray.carp
index 01bb5fad..c9e422f5 100644
--- a/core/StaticArray.carp
+++ b/core/StaticArray.carp
@@ -52,6 +52,7 @@
   (doc empty? "checks whether the array `a` is empty.")
   (defn empty? [a]
     (= (StaticArray.length a) 0))
+  (implements empty? StaticArray.empty?)
 
   (doc any? "checks whether any of the elements in `a` match the function `f`.")
   (defn any? [f a]
diff --git a/core/String.carp b/core/String.carp
index 5dce5c3c..9437881e 100644
--- a/core/String.carp
+++ b/core/String.carp
@@ -73,6 +73,7 @@
   (doc empty? "Check if the string is the empty string.")
   (defn empty? [s]
     (Int.= (length s) 0))
+  (implements empty? String.empty?)
 
   (doc slice "Return part of a string, beginning at index `a` and ending at index `b`.")
   (defn slice [s a b]
diff --git a/test/string.carp b/test/string.carp
index 11a79351..1a5747e9 100644
--- a/test/string.carp
+++ b/test/string.carp
@@ -72,7 +72,7 @@
                (empty? "")
                "empty? returns true on empty string")
   (assert-true test
-               (empty? &(zero))
+               (empty? &(the String (zero)))
                "empty? returns true on (zero)")
   (assert-equal test
                 &[\e \r \i \k]