Fix os.getenv error.

src/core/compile.c

@@ -133,6 +133,12 @@ void dstc_popscope(DstCompiler *c) {
         }
 
     }
+    /* Parent scopes inherit child's closure flag. Needed
+     * for while loops. (if a while loop creates a closure, it
+     * is compiled to a tail recursive iife) */
+    if (oldscope->flags & DST_SCOPE_CLOSURE) {
+        newscope->flags |= DST_SCOPE_CLOSURE;
+    }
     /* Free the old scope */
     dst_v_free(oldscope->consts);
     dst_v_free(oldscope->syms);

src/core/compile.h

@@ -90,6 +90,7 @@ struct DstSlot {
 #define DST_SCOPE_ENV 2
 #define DST_SCOPE_TOP 4
 #define DST_SCOPE_UNUSED 8
+#define DST_SCOPE_CLOSURE 16
 
 /* A symbol and slot pair */
 typedef struct SymPair {

src/core/os.c

@@ -153,6 +153,9 @@ static int os_getenv(DstArgs args) {
     DST_ARG_STRING(k, args, 0);
     const char *cstr = (const char *) k;
     const char *res = getenv(cstr);
+    if (!res) {
+        DST_RETURN_NIL(args);
+    }
     DST_RETURN(args, cstr
             ? dst_cstringv(res)
             : dst_wrap_nil());

src/include/dst/dst.h

@@ -1152,7 +1152,7 @@ int dst_lib_compile(DstArgs args);
 #define DST_ARG_CFUNCTION(DEST, A, N) _DST_ARG(DST_CFUNCTION, cfunction, DEST, A, N)
 #define DST_ARG_ABSTRACT(DEST, A, N) _DST_ARG(DST_ABSTRACT, abstract, DEST, A, N)
 
-#define DST_RETURN_NIL(A) return DST_SIGNAL_OK
+#define DST_RETURN_NIL(A) do { return DST_SIGNAL_OK; } while (0)
 #define DST_RETURN_FALSE(A) DST_RETURN(A, dst_wrap_false())
 #define DST_RETURN_TRUE(A) DST_RETURN(A, dst_wrap_true())
 #define DST_RETURN_BOOLEAN(A, X) DST_RETURN(A, dst_wrap_boolean(X))