A recent(?) update to swipl changed the error format from
Warning: some.pl:2:
Singleton variables: [Y]
to
Warning: some.pl:2:
Warning: Singleton variables: [Y]
The old error handler doesn't report the correct line numbers and
messages on the old format.
I've chosen to add a function that covers the second case and detect it,
rather than rewrite the current function. This way, both versions should
be able to live together.
---
Example file that demonstrates the issue (some.pl above):
```
% vim: ft=prolog
ii(X, Y) :- X.
```
---
D. Ben Knoble