From 72685517372587b8f3cdcb59d6029fcb017a07ea Mon Sep 17 00:00:00 2001
From: Patrick Pelissier <patrick.pelissier@gmail.com>
Date: Sun, 13 Mar 2022 18:53:35 +0100
Subject: [PATCH] Add micro utilities macros for handling list

---
 m-core.h           | 13 +++++++++++++
 tests/test-mcore.c | 10 ++++++++++
 2 files changed, 23 insertions(+)

diff --git a/m-core.h b/m-core.h
index 4a504124..9b2d3bc5 100644
--- a/m-core.h
+++ b/m-core.h
@@ -1675,6 +1675,19 @@ M_BEGIN_PROTECTED_CODE
 #define M_FILTER_00(d, item)                                                  \
   M_IF(M_PAIR_1 d(M_PAIR_2 d, item))(item, )
 
+/* Return the HEAD element of a list */
+#define M_HEAD(x, ...)      x
+
+/* Return the HEAD element of the tail of a list */
+#define M_HEAD_2(x, y, ...) y
+
+/* Return the tail sublist of the list (removing the HEAD) */
+#define M_TAIL(x, ...)      __VA_ARGS__
+
+/* Return the tail sublist of the sublist (removing the 2 first elements) */
+#define M_TAIL_2(x, y, ...) __VA_ARGS__
+
+
 /* Concatene two arglists 'a' and 'b',
    handling the case of empty arglist
    handling the cases where the arglists are within parenthesis.
diff --git a/tests/test-mcore.c b/tests/test-mcore.c
index 872f4239..9e8f9b82 100644
--- a/tests/test-mcore.c
+++ b/tests/test-mcore.c
@@ -758,6 +758,15 @@ static void test_properties(void)
   assert( M_GET_PROPERTY (OP_PROP(), IT_TYPE ) == 2);
   assert( M_KEYWORD_P( M_GET_PROPERTY (OP_PROP(), INIT_WITH ), priority));
 }
+
+static void test_generic_api(void)
+{
+  assert( M_HEAD(17, 0) == 17);
+  assert( M_TAIL(18, 19) == 19);
+  assert( M_HEAD_2(18, 17, 0) == 17);
+  assert( M_TAIL_2(18, 17, 8) == 8);
+}
+
 int main(void)
 {
   test_cat();
@@ -783,5 +792,6 @@ int main(void)
   test_str_hash();
   test_M_CSTR();
   test_properties();
+  test_generic_api();
   exit(0);
 }