Update `array_sum` example

examples/array_sum/as.fut

 entry array_sum (xs: []i64) : i64 = i64.sum xs
-entry self (xs: i64) : i64 = xs

examples/array_sum/main.c

@@ -8,43 +8,36 @@
 // Internal
 #include "as.h"
 
-#define LENGTH_X 8
-#define LENGTH_Y 8
-#define LENGTH_Z 1
-#define ARRAY_LENGTH (LENGTH_X) * (LENGTH_Y) * (LENGTH_Z)
-
 #define T int64_t
 
-FMPI_TASK_FUTHARK_SYNC(array_sum, 1)
+FMPI_TASK_FUTHARK(array_sum, 1)
 
 int main(int argc, char * argv[])
 {
     struct fmpi_ctx * ctx = fmpi_init(&argc, &argv);
     if(ctx == NULL) {
         fprintf(stderr, "fmpi_init() failed!\n");
-        fmpi_abort();
+        return EXIT_FAILURE;
     }
-    T in[64] = {
-        17,0,0,0,0,0,0,0,
-        0,0,0,0,0,0,0,0,
-        17,0,0,0,0,0,0,0,
-        0,0,0,0,0,0,0,0,
-        17,0,0,0,0,0,0,0,
-        0,0,0,0,0,0,0,0,
-        17,0,0,0,0,0,0,0,
-        0,0,0,0,0,0,0,0,
+    T in[] = {
+        1,0,0,0,0,0,0,0,
+        0,0,0,0,0,0,0,1, 
+        2,0,0,0,0,0,0,0,
+        0,0,0,0,0,0,0,2,
+        3,0,0,0,0,0,0,0,
+        0,0,0,0,0,0,0,3,
+        4,0,0,0,0,0,0,0,
+        0,0,0,0,0,0,0,4
     };
-    T out;
+    const size_t in_size = sizeof(in)/sizeof(T);
+    T out = -1;
     struct fmpi_task array_sum_task = FMPI_TASK_REGISTER(
-        ctx, array_sum,
+        ctx, array_sum, fmpi_no_stencil(),
         fmpi_data_1d_out(ctx, &out, 1),
-        fmpi_data_1d_in_new(ctx, in, 64)
+        fmpi_data_1d_in(ctx, in, in_size)
     );
-    fmpi_task_run(ctx, &array_sum_task);
-    if(fmpi_is_root(ctx)) {
-        printf("sum=%ld\n", *(T*)array_sum_task.args.out.start);
-        printf("sum=%ld\n", out);
-    }
+    fmpi_task_run_sync(ctx, &array_sum_task);
+    printf("rank=%d sum=%ld\n", fmpi_world_rank(ctx), out);
     fmpi_exit(&ctx);
     return EXIT_SUCCESS;
 }