From f2d5de252b74f1d97365ea4312f4e049fbb1a549 Mon Sep 17 00:00:00 2001
From: Patrick Pelissier <patrick.pelissier@gmail.com>
Date: Sat, 6 Feb 2021 23:24:55 +0100
Subject: [PATCH] Add M_FILTER and M_FILTER_C macros (src, tests, doc)

---
 README.md          | 17 +++++++++++++++++
 m-core.h           | 30 ++++++++++++++++++++++++++++++
 tests/test-mcore.c | 11 +++++++++++
 3 files changed, 58 insertions(+)

diff --git a/README.md b/README.md
index adf82d19..b8d4a9e6 100644
--- a/README.md
+++ b/README.md
@@ -5710,6 +5710,23 @@ Replicate the value 'value' N times, separating then by commas.
         ==>
         D , D , D , D , D
 
+##### M\_FILTER(func, data, ...)
+
+Filter the arglists by keeping only the element that match the function 'func(data, element)'
+
+       M_FILTER(M_NOTEQUAL, 8, 1, 3, 4, 8, 9, 8, 10)
+       ==>
+       1 3 4 9 10
+
+##### M\_FILTER\_C(func, data, ...)
+
+Filter the arglists by keeping only the element that match the function 'func(data, element)'
+separated by commas.
+
+       M_FILTER(M_NOTEQUAL, 8, 1, 3, 4, 8, 9, 8, 10)
+       ==>
+       1 , 3 , 4 , 9 , 10
+
 ##### M\_NARGS(args...)
 
 Return the number of argument of the given list.
diff --git a/m-core.h b/m-core.h
index 86ab5a7d..ecca701b 100644
--- a/m-core.h
+++ b/m-core.h
@@ -1575,6 +1575,36 @@ M_BEGIN_PROTECTED_CODE
 #define M_REPLICATE_C(N, value)                    \
   M_MAP2_C(M_RET_ARG1, value, M_SEQ(1, N))
 
+/* Filter the elements of the list so that only the elements
+   that match the function f are returned.
+   f takes as argument (extra, item) and shall return 0 or 1. */
+#define M_FILTER(f, extra, ...)                     \
+  M_MAP2( M_FILTER_00, (f, extra), __VA_ARGS__)
+
+/* Filter the elements of the list so that only the elements
+   that match the function f are returned.
+   f takes as argument (extra, item) and shall return 0 or 1. */
+#define M_FILTER_C(f, extra, ...)                                   \
+  M_REMOVE_PARENTHESIS (M_REDUCE2(M_FILTER_00, M_CAT_ARGLIST, (f, extra), __VA_ARGS__) )
+
+/* d is (filter_function, extra_value) item is the element ot test */
+#define M_FILTER_00(d, item)                    \
+  M_IF(M_PAIR_1 d(M_PAIR_2 d, item))(item, )
+
+/* Concatene two arglists 'a' and 'b',
+   handling the case of empty arglist
+   handling the cases where the arglists are within parenthesis.
+   and returning an arglist within parenthesis if it concats.
+   (internal macro)
+*/
+#define M_CAT_ARGLIST(a, b)                                       \
+  M_IF_EMPTY(a)(b, M_IF_EMPTY(b)(a,( M_REMOVE_PARENTHESIS (a) , M_REMOVE_PARENTHESIS (b))))
+
+/* Remove the parenthesis if needed
+   (internal macro) */
+#define M_REMOVE_PARENTHESIS(list)              \
+  M_IF(M_PARENTHESIS_P(list))( M_OPFLAT list, list)
+
 /* Return the input (delay evaluation) */
 #define M_ID(...)                 __VA_ARGS__
 
diff --git a/tests/test-mcore.c b/tests/test-mcore.c
index 31cd27f3..64385633 100644
--- a/tests/test-mcore.c
+++ b/tests/test-mcore.c
@@ -305,10 +305,21 @@ static void test_list(void)
   assert(M_KEEP_ARGS(1, 1, 0, 0, 0, 0));
   assert(M_SKIP_ARGS(4, 0, 0, 0, 0, 1));
   assert(M_MID_ARGS(2, 1, 0, 0, 1, 0));
+
   const int tab[] = { M_REPLICATE_C(5, 1) };
   for(int i = 0; i < 5; i++) assert(tab[i] == 1);
   const char str[] = M_REPLICATE(10, "N");
   assert(strcmp(str, "NNNNNNNNNN") == 0);
+
+  assert(M_EQUAL(M_REMOVE_PARENTHESIS( 17 ), 17));
+  assert(M_EQUAL(M_REMOVE_PARENTHESIS( (17) ), 17));
+
+  assert( M_FILTER(M_EQUAL, 17, 1, 42, 17, 89) );
+  assert( M_FILTER_C(M_EQUAL, 17, 1, 42, 17, 89) );
+  const int tab2[] = { M_FILTER_C(M_NOTEQUAL, 8, 1, 3, 4, 8, 9, 8, 10) };
+  const int tabref[] = { 1, 3, 4, 9, 10 };
+  assert (sizeof tab2 == sizeof tabref);
+  for(int i = 0; i < 5 ; i++) assert(tab2[i] == tabref[i]);
 }
 
 static void test_oplist(void)