for tests/spirit: replace 'nil' by 'leer' since 'nil' leads to conflict with macOS.

src/tests/spirit/PFunction.cpp

@@ -158,11 +158,11 @@ double PFunction::Eval()
 //==========================================================================
 
 /**
- * @brief Evaluates a nil (empty) AST node.
+ * @brief Evaluates a leer (empty) AST node.
  *
  * @return Always returns 0.0
  */
-double PFunction::EvalVisitor::operator()(const musrfit::ast::nil&) const
+double PFunction::EvalVisitor::operator()(const musrfit::ast::leer &) const
 {
   return 0.0;
 }

src/tests/spirit/PFunction.h

@@ -129,11 +129,11 @@ class PFunction {
         : fMap(map), fParam(param) {}
 
       /**
-       * @brief Evaluates a nil/empty AST node.
-       * @param AST nil node (unused)
+       * @brief Evaluates a leer/empty AST node.
+       * @param AST leer node (unused)
        * @return 0.0
        */
-      double operator()(const musrfit::ast::nil&) const;
+      double operator()(const musrfit::ast::leer&) const;
 
       /**
        * @brief Evaluates a numeric literal.

src/tests/spirit/PFunctionAst.h

@@ -107,7 +107,7 @@ namespace musrfit { namespace ast
      *
      * Used as a placeholder in variant types where no value is present.
      */
-    struct nil {};
+    struct leer {};
 
     // Forward declarations for recursive AST structures
     struct expression;
@@ -173,7 +173,7 @@ namespace musrfit { namespace ast
      * recursive grammar structures.
      */
     typedef boost::variant<
-            nil                                      ///< Empty placeholder
+            leer                                     ///< Empty placeholder
           , double                                   ///< Numeric literal
           , constant                                 ///< Constant value
           , parameter                                ///< Parameter reference
@@ -246,11 +246,11 @@ namespace musrfit { namespace ast
     };
 
     /**
-     * @brief Stream output operator for nil nodes (debugging support).
+     * @brief Stream output operator for leer nodes (debugging support).
      * @param out the output stream
      * @return the output stream for chaining
      */
-    inline std::ostream& operator<<(std::ostream& out, nil) { out << std::string("nil"); return out; }
+    inline std::ostream& operator<<(std::ostream& out, leer) { out << std::string("leer"); return out; }
 }}
 
 // Boost.Fusion adaptations to make structures compatible with X3 attribute propagation