diff --git a/6.0s1.h b/6.0s1.h
index ba18906..68693d9 100644
--- a/6.0s1.h
+++ b/6.0s1.h
@@ -6,6 +6,7 @@
 struct s1_location {
     const char *file;
     int line;
+    const char *func;
 };
 
 typedef int32_t   s1_int;
@@ -14,7 +15,7 @@ typedef double    s1_double;
 typedef char      s1_char;
 
 
-#define S1_LOC() (struct s1_location){__FILE__, __LINE__}
+#define S1_LOC() (struct s1_location){__FILE__, __LINE__, __func__}
 
 #   ifndef S1_6_0_H_IMPL
 
@@ -24,13 +25,13 @@ typedef char      s1_char;
 // 1. assert 
 void s1_assert(int value, const char *reason, struct s1_location loc) {
     if (!value) {
-        fprintf(stderr, "%s:%d %s\n", loc.file, loc.line, reason);
+        fprintf(stderr, "%s:%d [in %s] %s\n", loc.file, loc.line, loc.func, reason);
         exit(3);
     }
 }
 
 void s1_trace(const char *text, struct s1_location loc) {
-    fprintf(stderr, "Trace: %s:%d: %s\n", loc.file, loc.line, text);
+    fprintf(stderr, "Trace: %s:%d: [in %s] %s\n", loc.file, loc.line, loc.func, text);
 }
 
 
@@ -39,23 +40,23 @@ void s1_trace(const char *text, struct s1_location loc) {
 // 2. simple IO
 
 void write_int(s1_int value, struct s1_location loc) {
-    int rc = printf(PRId32, value);
-    s1_assert(rc != EOF, "Error: write_int", loc);
+    int rc = printf("%" PRId32, value);
+    s1_assert(rc != EOF, "write_int: IOError", loc);
 }
 
 void write_long(s1_long value, struct s1_location loc) {
-    int rc = printf(PRId64, value);
-    s1_assert(rc != EOF, "Error: write_long", loc);
+    int rc = printf("%" PRId64, value);
+    s1_assert(rc != EOF, "write_long: IOError", loc);
 }
 
 void write_double(s1_double value, struct s1_location loc) {
     int rc = printf("%lf", value);
-    s1_assert(rc != EOF, "Error: write_long", loc);
+    s1_assert(rc != EOF, "write_double: IOError", loc);
 }
 
 void write_char(s1_char value, struct s1_location loc) {
     int rc = printf("%c", value);
-    s1_assert(rc != EOF, "Error: write_char", loc);
+    s1_assert(rc != EOF, "write_char: IOError", loc);
 }
 
 #       define write_int(value)      write_int(value, S1_LOC())
@@ -65,29 +66,29 @@ void write_char(s1_char value, struct s1_location loc) {
 
 s1_int read_int(struct s1_location loc) {
     s1_int value = 0;
-    int rc = scanf(SCNd32, &value);
-    s1_assert(rc == 1, "Error: read_int", loc);
+    int rc = scanf("%" SCNd32, &value);
+    s1_assert(rc == 1, "read_int: IOError", loc);
     return value;
 }
 
 s1_long read_long(struct s1_location loc) {
     s1_long value = 0;
-    int rc = scanf(SCNd64, &value);
-    s1_assert(rc == 1, "Error: read_long", loc);
+    int rc = scanf("%" SCNd64, &value);
+    s1_assert(rc == 1, "read_long: IOError", loc);
     return value;
 }
 
 s1_double read_double(struct s1_location loc) {
     s1_double value = 0.0;
     int rc = scanf("%lf", &value);
-    s1_assert(rc == 1, "Error: read_double", loc);
+    s1_assert(rc == 1, "read_double: IOError", loc);
     return value;
 }
 
 s1_char read_char(struct s1_location loc) {
     s1_char value = 0;
     int rc = scanf("%c", &value);
-    s1_assert(rc == 1, "Error: read_char", loc);
+    s1_assert(rc == 1, "read_char: IOError", loc);
     return value;
 }
 
@@ -98,7 +99,7 @@ void read_pnl(struct s1_location loc) {
         if (feof(stdin)) {
             break;
         }
-        s1_assert(rc == 1, "Error: read_pnl", loc);
+        s1_assert(rc == 1, "read_pnl: IOError", loc);
         if (value == '\n') {
             break;
         }