lumiera_error_expect() lets one easily handle expected errors

This is a convenience function which clears the error state when some
expected error occurred and lets one branch on this.

src/lib/error.c

@@ -134,3 +134,19 @@ lumiera_error_peek (void)
 {
   return lumiera_error_get ()->err;
 }
+
+int
+lumiera_error_expect (lumiera_err expected)
+{
+  LumieraErrorcontext self = lumiera_error_get ();
+  lumiera_err err = self->err;
+
+  if (err == expected)
+    {
+      if (err)
+        self->err = NULL;
+      return 1;
+    }
+  else
+    return 0;
+}

src/lib/error.h

@@ -160,6 +160,17 @@ lumiera_err
 lumiera_error_peek (void);
 
 
+/**
+ * Expect some error
+ * Check that the current error state matches some expectation, if true then the error state
+ * is cleared and 1 is returned, otherwise 0 is returned and the error state remains set.
+ * @param expected error which is expected
+ * @return 1 if the current error state equals the expected state, else 0, the error state is cleared when the expectation is met
+ */
+int
+lumiera_error_expect (lumiera_err expected);
+
+
 /*
   predefined errors
 */