feat(example): demo invoke macro, better macro msg

example/invoke-via-macro.F90

@@ -0,0 +1,25 @@
+#include "../src/assert/assert_macros.h"
+
+program invoke_via_macro
+  !! Demonstrate how to invoke the 'assert' subroutine using a preprocessor macro that facilitates
+  !! the complete removal of the call in the absence of the compiler flag -DDEBUG.
+  use assert_m, only : assert, intrinsic_array_t, string
+    !! If an "only" clause is employed as above, it must include the "string" function that the
+    !! call_assert* macros reference when transforming the code below into "assert" subroutine calls.
+  implicit none
+
+#ifndef DEBUG
+  print *
+  print *,'To enable the "assert" call, define -DDEBUG, e.g., fpm run --example invoke-via-macro --flag "-DDEBUG -fcoarray=single"'
+  print *
+#endif
+
+  ! The C preprocessor will convert each call_assert* macro below into calls to the "assert" subroutine 
+  ! (if -DDEBUG is in the compiler command) or into nothing (if -DDEBUG is not in the compiler command).
+
+  call_assert(1==1) ! true assertion
+  call_assert_describe(2>0,    "example assertion invocation via macro") ! true assertion
+  call_assert_diagnose(1+1==2, "example with scalar diagnostic data", 1+1) ! true assertion
+  call_assert_diagnose(1+1>2,  "example with array diagnostic data" , intrinsic_array_t([1,1,2])) ! false assertion
+
+end program invoke_via_macro

src/assert/assert_macros.h

@@ -1,6 +1,6 @@
 #ifdef DEBUG
-# define call_assert(assertion) call assert(assertion, "file " // __FILE__ // ", line " // string(__LINE__))
-# define call_assert_describe(assertion, description) call assert(assertion, "file " // __FILE__ // ", line " // string(__LINE__) // ": " // description)
+# define call_assert(assertion) call assert(assertion, "No description provided (see file " // __FILE__ // ", line " // string(__LINE__) // ")")
+# define call_assert_describe(assertion, description) call assert(assertion, description // " in file " // __FILE__ // ", line " // string(__LINE__) // ": " )
 # define call_assert_diagnose(assertion, description, diagnostic_data) call assert(assertion, "file " // __FILE__ // ", line " // string(__LINE__) // ": " // description, diagnostic_data)
 #else
 # define call_assert(assertion)