formula: is_literal should be const

Reported by Ayrat Khalimov. * spot/tl/formula.hh (is_literal): Mark as const.

formula: is_literal should be const
Reported by Ayrat Khalimov. * spot/tl/formula.hh (is_literal): Mark as const.
4d226260 · Alexandre Duret-Lutz · 8ffd06e9 · 4d226260
Commit 4d226260 authored Dec 02, 2021 by Alexandre Duret-Lutz
--- a/spot/tl/formula.hh
+++ b/spot/tl/formula.hh
@@ -1557,7 +1557,7 @@ namespace spot

    /// \brief Whether the formula is an atomic proposition or its
    /// negation.
-    bool is_literal()
+    bool is_literal() const
    {
      return (is(op::ap) ||
          // If f is in nenoform, Not can only occur in front of