From 8dafe3b7a6a6122f845e8ae9249a7ff85b8fe17c Mon Sep 17 00:00:00 2001
From: Patrick Pelissier <patrick.pelissier@gmail.com>
Date: Wed, 4 Jul 2018 17:39:03 +0200
Subject: [PATCH] Add macro M_GET_AT.

---
 README.md          | 14 ++++++++++++++
 m-core.h           |  9 +++++++++
 tests/test-mcore.c |  3 +++
 3 files changed, 26 insertions(+)

diff --git a/README.md b/README.md
index 1f5df4f3..6fc9d93e 100644
--- a/README.md
+++ b/README.md
@@ -3920,6 +3920,20 @@ Keep the medium arguments of the argument list,
 starting from the 'first'-th one and up to 'len' arguments.
 first and len can be within [0..52].
 
+
+##### M\_GET\_AT(array, index)
+
+Return the index 'index' of the "array" 'array'.
+array in this context is a list of arguments encapsulated with parenthesis,
+and is not a true C array.
+Return the pre-processing token corresponding to this value (meaning it is evaluated
+at macro processing stage, not at compiler stage).
+
+Example:
+
+        M_GET_AT((f_0,f_1,f_2),1)
+
+
 ##### M\_BOOL(cond)
 
 Convert an integer or a symbol into 0 (if 0) or 1 (if not 0 or symbol unknown).
diff --git a/m-core.h b/m-core.h
index b5a5b954..b38c3331 100644
--- a/m-core.h
+++ b/m-core.h
@@ -622,6 +622,15 @@
 #define M_MID(first, len, ...) M_MIDI(M_KEEP,len, M_SKIP(first, __VA_ARGS__))
 #define M_MIDI(f, ...) f(__VA_ARGS__)
 
+
+/* Return the value of the "array" associated to the given index.
+   EXAMPLE: M_GET_AT((f_0,f_1,f_2),1) returns f_1
+   Can be chained with NARGS().
+ */
+#define M_GET_AT(array, index)   M_GETI_AT0(M_C(M_RET_ARG,M_INC(index)), array)
+#define M_GETI_AT0(func, array)  func ( M_ID array , dummy )
+
+
 /* Convert an integer or a symbol into 0 (if 0) or 1 (if not 0).
    1 if symbol unknown */
 #define M_TOBOOLI_0                 1, 0,
diff --git a/tests/test-mcore.c b/tests/test-mcore.c
index 170066d6..0c63aeae 100644
--- a/tests/test-mcore.c
+++ b/tests/test-mcore.c
@@ -120,6 +120,9 @@ static void test_return(void)
   assert (M_RET_ARG2(0, 1, 0));
   assert (M_RET_ARG3(0, 0, 1, 0));
   assert (M_RET_ARG27(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ,0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0));
+  assert (M_GET_AT((0,1,0),1));
+  assert (M_GET_AT((1,0,0),0));
+  assert (M_GET_AT((0,0,0,1),3));
 }
 
 static void test_invert(void)