refactor code

configure.ac

@@ -26,7 +26,7 @@ case "${host_os}" in
 esac
 
 dnl Checks for programs.
-AC_PROG_CC_C99
+AC_PROG_CC_STDC
 
 dnl Checks for header files.
 AC_CHECK_HEADERS([arpa/inet.h inttypes.h stddef.h stdint.h stdlib.h string.h unistd.h],

src/runtime.c

@@ -206,7 +206,7 @@ u6a_runtime_init(struct u6a_runtime_options* options) {
     return false;
 }
 
-U6A_HOT union u6a_vm_var
+U6A_HOT struct u6a_vm_var_fn
 u6a_runtime_execute(FILE* restrict istream, FILE* restrict ostream) {
     struct u6a_vm_var_fn acc = { 0 }, top = { 0 };
     struct u6a_vm_ins* ins = text + text_subst_len;
@@ -345,7 +345,7 @@ u6a_runtime_execute(FILE* restrict istream, FILE* restrict ostream) {
                         VM_JMP(0x03);
                     case u6a_vf_e:
                         // Every program should terminate with explicit `e` function
-                        return U6A_VM_VAR_FN(arg);
+                        return arg;
                     default:
                         CHECK_FORCE(u6a_err_invalid_vm_func, func.token.fn);
                 }
@@ -365,6 +365,9 @@ u6a_runtime_execute(FILE* restrict istream, FILE* restrict ostream) {
                     ACC_FN_REF(u6a_vf_d1_s, u6a_vm_pool_alloc2(func, arg));
                 } else {
                     acc = u6a_vm_stack_xch(acc);
+                    if (UNLIKELY(U6A_VM_VAR_FN_IS_EMPTY(acc))) {
+                        goto runtime_error;
+                    }
                 }
                 break;
             case u6a_vo_del:
@@ -387,7 +390,7 @@ u6a_runtime_execute(FILE* restrict istream, FILE* restrict ostream) {
     }
 
     runtime_error:
-    return U6A_VM_VAR_PTR(NULL);
+    return U6A_VM_VAR_FN_EMPTY;
 }
 
 void

src/runtime.h

@@ -40,7 +40,7 @@ u6a_runtime_info(FILE* restrict istream, const char* file_name);
 bool
 u6a_runtime_init(struct u6a_runtime_options* options);
 
-union u6a_vm_var
+struct u6a_vm_var_fn
 u6a_runtime_execute(FILE* restrict istream, FILE* restrict output_stream);
 
 void

src/u6a.c

@@ -153,8 +153,8 @@ int main(int argc, char** argv) {
         exit_code = EC_ERR_INIT;
         goto terminate;
     }
-    union u6a_vm_var exec_result = u6a_runtime_execute(stdin, stdout);
+    struct u6a_vm_var_fn exec_result = u6a_runtime_execute(stdin, stdout);
-    if (UNLIKELY(exec_result.ptr == NULL)) {
+    if (UNLIKELY(U6A_VM_VAR_FN_IS_EMPTY(exec_result))) {
         exit_code = EC_ERR_RUNTIME;
         goto terminate;
     }

src/vm_defs.h

@@ -89,6 +89,8 @@ struct u6a_vm_var_fn {
 };
 
 #define U6A_VM_VAR_FN_REF(fn_, ref_) (struct u6a_vm_var_fn) { .token.fn = (fn_), .ref = (ref_) }
+#define U6A_VM_VAR_FN_EMPTY          (struct u6a_vm_var_fn) { 0 }
+#define U6A_VM_VAR_FN_IS_EMPTY(fn_)  ( ((union u6a_vm_var)(fn_)).ptr == NULL )
 
 union u6a_vm_var {
     struct u6a_vm_var_fn fn;

src/vm_stack.c

@@ -108,7 +108,7 @@ u6a_vm_stack_top() {
     if (UNLIKELY(vs->top == UINT32_MAX)) {
         vs = vs->prev;
         if (UNLIKELY(vs == NULL)) {
-            return (struct u6a_vm_var_fn) { 0 };
+            return U6A_VM_VAR_FN_EMPTY;
         }
         active_stack = vs;
     }
@@ -232,12 +232,13 @@ u6a_vm_stack_xch(struct u6a_vm_var_fn v0) {
     } else {
         struct vm_stack* prev = vs->prev;
         if (UNLIKELY(prev == NULL)) {
-            return (struct u6a_vm_var_fn) { 0 };
+            u6a_err_stack_underflow(err_stage);
+            return U6A_VM_VAR_FN_EMPTY;
         }
         if (--prev->refcnt > 0) {
             prev = vm_stack_dup(prev);
             if (UNLIKELY(prev == NULL)) {
-                return (struct u6a_vm_var_fn) { 0 };
+                return U6A_VM_VAR_FN_EMPTY;
             }
         }
         if (vs->top == 0) {