Warn about deeply nested negation

mthom · Oct 7, 2024 · 2d1ebf0 · 2d1ebf0
1 parent be3e011
commit 2d1ebf0
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Showing 3 changed files with 13 additions and 1 deletion.
diff --git a/src/lib/warnings.pl b/src/lib/warnings.pl
@@ -48,3 +48,11 @@
     unsound_type_test(G),
     functor(G, F, 1),
     warn_fail("~q is a constant source of bugs, use ~a_si/1 from library(si)", [F/1,F]).
+
+% Warn when more than 2 negations are nested. Double negation has legit
+% use-case, but I don't think that more nested negations are ever useful.
+%
+user:goal_expansion(G, _) :-
+    nonvar(G),
+    G = (\+ \+ \+ _),
+    warn_fail("Nested negations can be reduced", []).
diff --git a/src/tests/warnings.pl b/src/tests/warnings.pl
@@ -3,6 +3,9 @@
 t :-
     x; integer(_).
 
+n :-
+    \+ \+ \+ foo(_).
+
 x :-
     a.
     b,

diff --git a/tests/scryer/cli/src_tests/warnings_tests.stderr b/tests/scryer/cli/src_tests/warnings_tests.stderr
@@ -1,2 +1,3 @@
 % Warning: integer/1 is a constant source of bugs, use integer_si/1 from library(si) at line 4 of warnings.pl
-% Warning: (b,c) attempts to re-define (,)/2 at line 9 of warnings.pl
+% Warning: Nested negations can be reduced at line 7 of warnings.pl
+% Warning: (b,c) attempts to re-define (,)/2 at line 12 of warnings.pl
-Original file line number
+Diff line change
@@ Expand Up / @@ -3,6 +3,9 @@ @@
     t :-
         x; integer(_).
+    n :-
+        \+ \+ \+ foo(_).
     x :-
         a.
         b,
@@ Expand Down @@