small refactor and cleanup

tests/io_write_file.sl

@@ -0,0 +1,17 @@
+import ../stdlib/stdlib.sl
+import ../stdlib/io.sl
+
+: main
+    "/tmp/l2_write_file_test.txt"  # path
+    "hello from write_file test\n" # buffer
+    write_file
+    dup 0 > if
+        "wrote bytes: " puts
+        puti cr
+        0
+        exit
+    end
+    "write failed errno=" puts
+    puti cr
+    exit
+;