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

src/classes/CMakeLists.txt

@@ -232,13 +232,16 @@ install(
 
 #--- install headers ----------------------------------------------------------
 install(
-  FILES ${MUSRFIT_INC}/PFitterFcn.h
+  FILES ${MUSRFIT_INC}/PFindRun.h
+        ${MUSRFIT_INC}/PFitterFcn.h
         ${MUSRFIT_INC}/PFitter.h
         ${MUSRFIT_INC}/PFourierCanvas.h
         ${MUSRFIT_INC}/PFourier.h
+        ${MUSRFIT_INC}/PFunctionAst.h 
         ${MUSRFIT_INC}/PFunctionGrammar.h
         ${MUSRFIT_INC}/PFunction.h
         ${MUSRFIT_INC}/PFunctionHandler.h
+        ${MUSRFIT_INC}/PMsgBox.h
         ${MUSRFIT_INC}/PMsr2Data.h
         ${MUSRFIT_INC}/PMsrHandler.h
         ${MUSRFIT_INC}/PMusrCanvas.h

src/classes/PFunctionHandler.cpp

@@ -30,8 +30,12 @@
 #include <string>
 #include <cassert>
 
+#include <boost/spirit/home/x3.hpp>
+
 #include "PFunctionHandler.h"
 
+namespace x3 = boost::spirit::x3;
+
 //-------------------------------------------------------------
 // Constructor
 //-------------------------------------------------------------
@@ -67,7 +71,6 @@ PFunctionHandler::~PFunctionHandler()
 Bool_t PFunctionHandler::DoParse()
 {
   Bool_t success = true;
-  PFunctionGrammar function;
   TString line;
 
   // feed the function block into the parser. Start with i=1, since i=0 is FUNCTIONS
@@ -89,14 +92,32 @@ Bool_t PFunctionHandler::DoParse()
     }
     line.ToUpper();
 
-    // do parsing
+    // do parsing with X3
-    tree_parse_info<> info = ast_parse(line.Data(), function, space_p);
+    musrfit::ast::assignment assignment;
+    std::string str(line.Data());
+    auto iter = str.begin();
+    auto end = str.end();
 
-    if (info.full) { // parsing successful
+    // Get the X3 grammar
-      PFunction func(info); // generate an evaluation function object based on the AST tree
+    auto const& grammar = musrfit::function_grammar();
-      fFuncs.push_back(func); // feeds it to the functions vector
+
-    } else {
+    try {
+      bool parseSuccess = x3::phrase_parse(iter, end, grammar, x3::space, assignment);
+
+      if (parseSuccess && iter == end) { // parsing successful
+        PFunction func(assignment); // generate an evaluation function object based on the AST
+        fFuncs.push_back(func); // feeds it to the functions vector
+      } else {
+        std::cerr << std::endl << "**ERROR**: FUNCTIONS parse failed in line " << fLines[i].fLineNo << std::endl;
+        if (iter != end) {
+          std::cerr << "**ERROR**: Stopped at: " << std::string(iter, end) << std::endl;
+        }
+        success = false;
+        break;
+      }
+    } catch (x3::expectation_failure<std::string::iterator> const& e) {
       std::cerr << std::endl << "**ERROR**: FUNCTIONS parse failed in line " << fLines[i].fLineNo << std::endl;
+      std::cerr << "**ERROR**: Expected: " << e.which() << std::endl;
       success = false;
       break;
     }

src/include/PFunction.h

@@ -8,7 +8,7 @@
 ***************************************************************************/
 
 /***************************************************************************
- *   Copyright (C) 2007-2025 by Andreas Suter                              *
+ *   Copyright (C) 2007-2026 by Andreas Suter                              *
  *   andreas.suter@psi.ch                                                  *
  *                                                                         *
  *   This program is free software; you can redistribute it and/or modify  *
@@ -33,85 +33,23 @@
 #include <vector>
 
 #include <boost/version.hpp>
-
+#include <boost/variant/static_visitor.hpp>
-#if BOOST_VERSION >= 103800
+#include <boost/variant/apply_visitor.hpp>
-#  include <boost/spirit/include/classic_ast.hpp>
-   using namespace BOOST_SPIRIT_CLASSIC_NS;
-#else
-#  include <boost/spirit/tree/ast.hpp>
-   using namespace boost::spirit;
-#endif
 
 #include <TString.h>
 
 #include "PMusr.h"
+#include "PFunctionAst.h"
 #include "PFunctionGrammar.h"
 
-//----------------------------------------------------------------------------
-// Operator tags for arithmetic operations
-//----------------------------------------------------------------------------
-#define OP_ADD 0  ///< Addition operator tag
-#define OP_SUB 1  ///< Subtraction operator tag
-#define OP_MUL 2  ///< Multiplication operator tag
-#define OP_DIV 3  ///< Division operator tag
-
-//----------------------------------------------------------------------------
-// Function tags for mathematical functions
-//----------------------------------------------------------------------------
-#define FUN_COS   0   ///< Cosine function tag
-#define FUN_SIN   1   ///< Sine function tag
-#define FUN_TAN   2   ///< Tangent function tag
-#define FUN_COSH  3   ///< Hyperbolic cosine function tag
-#define FUN_SINH  4   ///< Hyperbolic sine function tag
-#define FUN_TANH  5   ///< Hyperbolic tangent function tag
-#define FUN_ACOS  6   ///< Inverse cosine (arccos) function tag
-#define FUN_ASIN  7   ///< Inverse sine (arcsin) function tag
-#define FUN_ATAN  8   ///< Inverse tangent (arctan) function tag
-#define FUN_ACOSH 9   ///< Inverse hyperbolic cosine function tag
-#define FUN_ASINH 10  ///< Inverse hyperbolic sine function tag
-#define FUN_ATANH 11  ///< Inverse hyperbolic tangent function tag
-#define FUN_LOG   12  ///< Base-10 logarithm function tag
-#define FUN_LN    13  ///< Natural logarithm function tag
-#define FUN_EXP   14  ///< Exponential function tag
-#define FUN_SQRT  15  ///< Square root function tag
-#define FUN_POW   16  ///< Power function tag (base^exponent)
-
-//----------------------------------------------------------------------------
-/**
- * \brief Tree node structure for efficient function evaluation.
- *
- * This structure represents a node in the evaluation tree used to compute
- * function values. The abstract syntax tree (AST) generated by the parser
- * is converted into this more efficient tree structure for faster evaluation.
- *
- * Each node can represent:
- * - A leaf node (constant, parameter, map reference)
- * - An operator node (arithmetic operation)
- * - A function node (mathematical function)
- *
- * The tree is evaluated recursively by traversing from the root to the leaves.
- *
- * \see PFunction::EvalNode for the recursive evaluation algorithm
- */
-typedef struct func_tree_node {
-  Int_t    fID;          ///< Node type identifier (from PFunctionGrammar constants)
-  Int_t    fOperatorTag; ///< Operator type: OP_ADD, OP_SUB, OP_MUL, OP_DIV
-  Int_t    fFunctionTag; ///< Function type: FUN_COS, FUN_SIN, FUN_EXP, etc.
-  Int_t    fIvalue;      ///< Integer value for parameter numbers, map indices, or temperature indices
-  Bool_t   fSign;        ///< Sign flag: true for negative, false for positive
-  Double_t fDvalue;      ///< Numeric value for constants and real number literals
-  std::vector<func_tree_node> children; ///< Child nodes forming the sub-tree
-} PFuncTreeNode;
-
 //----------------------------------------------------------------------------
 /**
  * \brief Class for parsing and evaluating mathematical functions from msr-file FUNCTIONS blocks.
  *
  * This class handles the complete lifecycle of a function definition:
  * 1. Parses the function string using PFunctionGrammar into an AST
- * 2. Converts the AST into an efficient evaluation tree
+ * 2. Validates parameter and map references
- * 3. Validates parameter and map references
+ * 3. Evaluates the function with given parameters and metadata using the visitor pattern
- * 4. Evaluates the function with given parameters and metadata
  *
  * Functions can reference:
  * - Fit parameters (PAR1, PAR2, ...)
@@ -126,7 +64,7 @@ typedef struct func_tree_node {
  * \endcode
  *
  * \see PFunctionGrammar for the grammar definition
- * \see PFuncTreeNode for the evaluation tree structure
+ * \see musrfit::ast for the AST structure
  */
 class PFunction {
   public:
@@ -134,13 +72,13 @@ class PFunction {
     /**
      * \brief Constructor that parses and prepares a function for evaluation.
      *
-     * \param info Abstract syntax tree (AST) from parsing a function expression
+     * \param assignment Abstract syntax tree (AST) from parsing a function expression
      */
-    PFunction(tree_parse_info<> info);
+    PFunction(const musrfit::ast::assignment& assignment);
 
     //------------------------------------------------------------------------
     /**
-     * \brief Destructor that cleans up the evaluation tree.
+     * \brief Destructor that cleans up resources.
      */
     virtual ~PFunction();
 
@@ -202,101 +140,72 @@ class PFunction {
   protected:
     //------------------------------------------------------------------------
     /**
-     * \brief Initializes all fields of an evaluation tree node to default values.
+     * \brief Recursively validates parameter and map references in the AST.
      *
-     * \param node Node to initialize
+     * \param operand Current operand being checked
-     */
-    virtual void InitNode(PFuncTreeNode &node);
-
-    //------------------------------------------------------------------------
-    /**
-     * \brief Extracts the function number from the AST.
-     *
-     * Parses the function label (FUN#) to extract the numeric identifier.
-     *
-     * \return true if successful, false otherwise
-     */
-    virtual Bool_t SetFuncNo();
-
-    //------------------------------------------------------------------------
-    /**
-     * \brief Recursively validates parameter and map references in the tree.
-     *
-     * \param node Current node being checked
      * \param mapSize Number of available map entries
      * \param paramSize Number of available fit parameters
      * \return true if all references are valid, false otherwise
      */
-    virtual Bool_t FindAndCheckMapAndParamRange(PFuncTreeNode &node, UInt_t mapSize, UInt_t paramSize);
+    virtual Bool_t FindAndCheckMapAndParamRange(const musrfit::ast::operand& operand,
+                                                  UInt_t mapSize, UInt_t paramSize);
 
     //------------------------------------------------------------------------
     /**
-     * \brief Initiates the conversion from AST to evaluation tree.
+     * \brief Generates a human-readable string representation of the AST.
      *
-     * \return true if successful, false otherwise
+     * \param expr Expression AST to convert to string
+     * \return Formatted string representation
      */
-    virtual Bool_t GenerateFuncEvalTree();
+    virtual TString GenerateString(const musrfit::ast::expression& expr);
 
     //------------------------------------------------------------------------
     /**
-     * \brief Recursively builds the evaluation tree from the AST.
+     * \brief Generates a string representation of an operand.
      *
-     * \param i Iterator pointing to current AST node
+     * \param operand Operand AST to convert to string
-     * \param node Evaluation tree node to fill
+     * \return Formatted string representation
      */
-    virtual void FillFuncEvalTree(iter_t const& i, PFuncTreeNode &node);
+    virtual TString GenerateStringOperand(const musrfit::ast::operand& operand);
-
-    //------------------------------------------------------------------------
-    /**
-     * \brief Recursively evaluates an evaluation tree node.
-     *
-     * \param node Node to evaluate
-     * \return Computed value for this node and its subtree
-     */
-    virtual Double_t EvalNode(PFuncTreeNode &node);
-
-    //------------------------------------------------------------------------
-    /**
-     * \brief Initiates cleanup of the evaluation tree.
-     */
-    virtual void CleanupFuncEvalTree();
-
-    //------------------------------------------------------------------------
-    /**
-     * \brief Recursively cleans up evaluation tree nodes and their children.
-     *
-     * \param node Node to clean up
-     */
-    virtual void CleanupNode(PFuncTreeNode &node);
 
   private:
-    tree_parse_info<> fInfo;      ///< AST parse tree from Boost.Spirit parser
-    std::vector<Double_t> fParam; ///< Current fit parameter values for evaluation
-    std::vector<Int_t> fMap;      ///< Map vector for indirect parameter references
-    PFuncTreeNode fFunc;          ///< Root node of the evaluation tree
-
-    Bool_t fValid;  ///< Validity flag: true if function parsed and initialized successfully
-    Int_t fFuncNo;  ///< Function number extracted from label (x in FUNx)
-
-    //------------------------------------------------------------------------
     /**
-     * \brief Initiates generation of human-readable function string.
+     * \brief Visitor class for evaluating the AST.
      *
-     * \param info AST parse tree to convert to string
+     * This visitor traverses the AST and computes the numeric value of the expression.
+     * It uses the visitor pattern with boost::static_visitor to handle different
+     * AST node types.
      */
-    virtual void EvalTreeForString(tree_parse_info<> info);
+    class EvalVisitor : public boost::static_visitor<Double_t>
+    {
+    public:
+      EvalVisitor(const std::vector<Int_t>& map,
+                  const std::vector<Double_t>& param,
+                  const PMetaData& metaData)
+        : fMap(map), fParam(param), fMetaData(metaData) {}
 
-    //------------------------------------------------------------------------
+      Double_t operator()(const musrfit::ast::leer&) const;
-    /**
+      Double_t operator()(double val) const;
-     * \brief Recursively generates formatted function string from AST.
+      Double_t operator()(const musrfit::ast::constant& c) const;
-     *
+      Double_t operator()(const musrfit::ast::parameter& p) const;
-     * \param i Iterator pointing to current AST node
+      Double_t operator()(const musrfit::ast::map_ref& m) const;
-     * \param funcFlag Flag indicating if currently inside a function call
+      Double_t operator()(const musrfit::ast::function_call& f) const;
-     */
+      Double_t operator()(const musrfit::ast::power_call& p) const;
-    virtual void EvalTreeForStringExpression(iter_t const& i, bool funcFlag=false);
+      Double_t operator()(const musrfit::ast::expression& expr) const;
 
+    private:
+      const std::vector<Int_t>& fMap;
+      const std::vector<Double_t>& fParam;
+      const PMetaData& fMetaData;
+    };
+
+    musrfit::ast::expression fAst; ///< Abstract syntax tree for the expression
+    std::vector<Double_t> fParam;  ///< Current fit parameter values for evaluation
+    std::vector<Int_t> fMap;       ///< Map vector for indirect parameter references
+
+    Bool_t fValid;        ///< Validity flag: true if function parsed and initialized successfully
+    Int_t fFuncNo;        ///< Function number extracted from label (x in FUNx)
     TString fFuncString;  ///< Formatted, human-readable function representation
-
     PMetaData fMetaData;  ///< Metadata from experimental data (field, energy, temperature, etc.)
 };
 

src/include/PFunctionAst.h

@@ -0,0 +1,306 @@
+/***************************************************************************
+
+  PFunctionAst.h
+
+  Author: Andreas Suter
+  e-mail: andreas.suter@psi.ch
+
+  Abstract Syntax Tree (AST) definitions for Spirit X3 parser.
+  Migrated from Qi to X3 for improved compile times and cleaner syntax.
+
+***************************************************************************/
+
+/***************************************************************************
+ *   Copyright (C) 2007-2026 by Andreas Suter                              *
+ *   andreas.suter@psi.ch                                                  *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ *   This program is distributed in the hope that it will be useful,       *
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
+ *   GNU General Public License for more details.                          *
+ *                                                                         *
+ *   You should have received a copy of the GNU General Public License     *
+ *   along with this program; if not, write to the                         *
+ *   Free Software Foundation, Inc.,                                       *
+ *   59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.             *
+ ***************************************************************************/
+
+#ifndef _PFUNCTIONAST_H_
+#define _PFUNCTIONAST_H_
+
+#include <boost/config/warning_disable.hpp>
+#include <boost/variant/recursive_variant.hpp>
+#include <boost/fusion/include/adapt_struct.hpp>
+#include <boost/fusion/include/io.hpp>
+#include <boost/optional.hpp>
+#include <list>
+
+namespace musrfit { namespace ast
+{
+    ///////////////////////////////////////////////////////////////////////////
+    /**
+     * @brief Abstract Syntax Tree (AST) definitions for the function parser.
+     *
+     * This namespace defines the complete AST structure used to represent
+     * parsed function expressions. The AST is built using Boost.Variant for
+     * type-safe unions and Boost.Spirit X3's automatic AST generation from
+     * grammar rules.
+     *
+     * The AST supports:
+     * - Arithmetic operations: +, -, *, /
+     * - Mathematical functions: cos, sin, tan, exp, log, sqrt, pow, etc.
+     * - Constants: PI, GAMMA_MU, field (B), energy (EN), temperature (T#)
+     * - Parameter references: PAR#, -PAR#
+     * - Map references: MAP#
+     * - Function labels: FUN#
+     * - Expression evaluation with proper precedence
+     */
+    ///////////////////////////////////////////////////////////////////////////
+
+    /**
+     * @brief Enumeration of arithmetic operators.
+     *
+     * These tokens represent the fundamental arithmetic operations supported
+     * by the expression evaluator.
+     */
+    enum optoken
+    {
+      op_plus,     ///< Addition operator (+)
+      op_minus,    ///< Subtraction operator (-)
+      op_times,    ///< Multiplication operator (*)
+      op_divide,   ///< Division operator (/)
+    };
+
+    /**
+     * @brief Enumeration of supported mathematical functions.
+     *
+     * These function identifiers map to standard mathematical operations
+     * evaluated during the semantic analysis phase.
+     */
+    enum funid
+    {
+      fun_cos,   ///< Cosine function
+      fun_sin,   ///< Sine function
+      fun_tan,   ///< Tangent function
+      fun_cosh,  ///< Hyperbolic cosine function
+      fun_sinh,  ///< Hyperbolic sine function
+      fun_tanh,  ///< Hyperbolic tangent function
+      fun_acos,  ///< Arccosine function
+      fun_asin,  ///< Arcsine function
+      fun_atan,  ///< Arctangent function
+      fun_acosh, ///< Inverse hyperbolic cosine function
+      fun_asinh, ///< Inverse hyperbolic sine function
+      fun_atanh, ///< Inverse hyperbolic tangent function
+      fun_log,   ///< Base-10 logarithm function
+      fun_ln,    ///< Natural logarithm function
+      fun_exp,   ///< Exponential function
+      fun_sqrt   ///< Square root function
+    };
+
+    /**
+     * @brief Represents an empty/null AST node.
+     *
+     * Used as a placeholder in variant types where no value is present.
+     */
+    struct leer {};
+
+    // Forward declarations for recursive AST structures
+    struct expression;
+    struct function_call;
+    struct power_call;
+
+    /**
+     * @brief Represents a constant value in an expression.
+     *
+     * Constants can be:
+     * - Mathematical constants: PI, GAMMA_MU
+     * - Metadata values: B (field), EN (energy), T# (temperature)
+     */
+    struct constant
+    {
+      /**
+       * @brief Enumeration of constant types.
+       */
+      enum type {
+        pi,        ///< Mathematical constant π (3.14159...)
+        gamma_mu,  ///< Muon gyromagnetic ratio constant
+        field,     ///< Magnetic field from experimental data (B or -B)
+        energy,    ///< Energy from experimental data (EN or -EN)
+        temp       ///< Temperature from experimental data (T# or -T#)
+      };
+
+      type const_type;  ///< The type of constant
+      bool sign;        ///< Sign flag: false for positive, true for negative
+      int index;        ///< Index for temperature (T0, T1, T2, ...)
+    };
+
+    /**
+     * @brief Represents a parameter reference in an expression.
+     *
+     * Parameters are fit parameters referenced as PAR# or -PAR#,
+     * where # is the parameter number (1-based).
+     */
+    struct parameter
+    {
+      int number;  ///< Parameter number (extracted from PAR#)
+      bool sign;   ///< Sign flag: false for PAR#, true for -PAR#
+    };
+
+    /**
+     * @brief Represents a map reference in an expression.
+     *
+     * Maps provide indirect parameter references: MAP# or -MAP#
+     * references the map vector at index #-1, which then indexes
+     * into the parameter vector.
+     */
+    struct map_ref
+    {
+      int number;  ///< Map number (extracted from MAP#)
+      bool sign;   ///< Sign flag: false for MAP#, true for -MAP#
+    };
+
+    /**
+     * @brief Variant type representing any operand in an expression.
+     *
+     * An operand can be a literal number, constant, parameter, map reference,
+     * function call, power operation, or parenthesized expression. The variant
+     * uses recursive_wrapper for types that contain expressions to handle
+     * recursive grammar structures.
+     */
+    typedef boost::variant<
+            leer                                     ///< Empty placeholder
+          , double                                   ///< Numeric literal
+          , constant                                 ///< Constant value
+          , parameter                                ///< Parameter reference
+          , map_ref                                  ///< Map reference
+          , boost::recursive_wrapper<function_call>  ///< Function call (recursive)
+          , boost::recursive_wrapper<power_call>     ///< Power operation (recursive)
+          , boost::recursive_wrapper<expression>     ///< Parenthesized expression (recursive)
+        >
+    operand;
+
+    /**
+     * @brief Represents a binary operation with an operator and right operand.
+     *
+     * Used in expression chains where the left operand is the accumulated
+     * result from previous operations.
+     */
+    struct operation
+    {
+      optoken operator_; ///< The binary operator (+, -, *, /)
+      operand operand_;  ///< The right-hand operand
+    };
+
+    /**
+     * @brief Represents a complete expression with operator precedence.
+     *
+     * Expressions are built as a first operand followed by a sequence of
+     * operations. This structure naturally encodes operator precedence as
+     * determined by the grammar rules.
+     */
+    struct expression
+    {
+      operand first;            ///< The first operand in the expression
+      std::list<operation> rest; ///< Sequence of operations applied left-to-right
+    };
+
+    /**
+     * @brief Represents a function call with a single argument.
+     *
+     * Examples: COS(PAR1), SQRT(B), EXP(-PAR2 * T0)
+     */
+    struct function_call
+    {
+      funid func_id;    ///< The function identifier
+      expression arg;   ///< The argument expression
+    };
+
+    /**
+     * @brief Represents a power operation.
+     *
+     * Syntax: POW(base, exponent)
+     * Both base and exponent are full expressions.
+     */
+    struct power_call
+    {
+      expression base; ///< The base expression
+      expression pow;  ///< The exponent expression
+    };
+
+    /**
+     * @brief Represents an assignment statement.
+     *
+     * Syntax: FUN# = expression
+     * Assigns the result of evaluating the right-hand expression to a
+     * function label.
+     */
+    struct assignment
+    {
+      int func_number;  ///< Function number (extracted from FUN#)
+      expression rhs;   ///< The right-hand side expression to evaluate
+    };
+
+    /**
+     * @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, leer) { out << std::string("leer"); return out; }
+}}
+
+// Boost.Fusion adaptations to make structures compatible with X3 attribute propagation
+BOOST_FUSION_ADAPT_STRUCT(
+    musrfit::ast::constant,
+    (musrfit::ast::constant::type, const_type)
+    (bool, sign)
+    (int, index)
+)
+
+BOOST_FUSION_ADAPT_STRUCT(
+    musrfit::ast::parameter,
+    (int, number)
+    (bool, sign)
+)
+
+BOOST_FUSION_ADAPT_STRUCT(
+    musrfit::ast::map_ref,
+    (int, number)
+    (bool, sign)
+)
+
+BOOST_FUSION_ADAPT_STRUCT(
+    musrfit::ast::operation,
+    (musrfit::ast::optoken, operator_)
+    (musrfit::ast::operand, operand_)
+)
+
+BOOST_FUSION_ADAPT_STRUCT(
+    musrfit::ast::expression,
+    (musrfit::ast::operand, first)
+    (std::list<musrfit::ast::operation>, rest)
+)
+
+BOOST_FUSION_ADAPT_STRUCT(
+    musrfit::ast::function_call,
+    (musrfit::ast::funid, func_id)
+    (musrfit::ast::expression, arg)
+)
+
+BOOST_FUSION_ADAPT_STRUCT(
+    musrfit::ast::power_call,
+    (musrfit::ast::expression, base)
+    (musrfit::ast::expression, pow)
+)
+
+BOOST_FUSION_ADAPT_STRUCT(
+    musrfit::ast::assignment,
+    (int, func_number)
+    (musrfit::ast::expression, rhs)
+)
+
+#endif // _PFUNCTIONAST_H_

src/include/PFunctionGrammar.h

@@ -1,14 +1,17 @@
 /***************************************************************************
 
-  PFunctionGrammer.h
+  PFunctionGrammar.h
 
   Author: Andreas Suter
   e-mail: andreas.suter@psi.ch
 
+  Header-only grammar for parsing function entries in msr-file FUNCTION blocks.
+  This version uses Boost.Spirit X3 in header-only mode for maximum compatibility.
+
 ***************************************************************************/
 
 /***************************************************************************
- *   Copyright (C) 2007-2025 by Andreas Suter                              *
+ *   Copyright (C) 2007-2026 by Andreas Suter                              *
  *   andreas.suter@psi.ch                                                  *
  *                                                                         *
  *   This program is free software; you can redistribute it and/or modify  *
@@ -30,223 +33,296 @@
 #ifndef _PFUNCTIONGRAMMAR_H_
 #define _PFUNCTIONGRAMMAR_H_
 
-//#define BOOST_SPIRIT_DEBUG
+// Check Boost version - require 1.61+ for Spirit X3
-
 #include <boost/version.hpp>
-
+#if BOOST_VERSION < 106100
-#if BOOST_VERSION >= 103800
+#  error "Boost version 1.61.0 or higher is required for Spirit X3. Please upgrade Boost."
-#  include <boost/spirit/include/classic_core.hpp>
-#  include <boost/spirit/include/classic_ast.hpp>
-   using namespace BOOST_SPIRIT_CLASSIC_NS;
-#else
-#  include <boost/spirit/core.hpp>
-#  include <boost/spirit/tree/ast.hpp>
-   using namespace boost::spirit;
 #endif
 
-//--------------------------------------------------------------------------
+#include "PFunctionAst.h"
-/**
+#include <boost/spirit/home/x3.hpp>
- * \brief Iterator type for parsing characters.
- */
-typedef char const* iterator_t;
 
-//--------------------------------------------------------------------------
+namespace x3 = boost::spirit::x3;
-/**
- * \brief Type for parse tree matching results.
- */
-typedef tree_match<iterator_t> parse_tree_match_t;
 
-//--------------------------------------------------------------------------
 /**
- * \brief Iterator type for traversing the parse tree.
+ * @namespace musrfit::grammar
+ * @brief Boost.Spirit X3 grammar definitions for parsing function expressions.
+ *
+ * This namespace contains the complete grammar for parsing msr-file FUNCTION
+ * block entries. The grammar supports arithmetic expressions with operator
+ * precedence, mathematical functions, constants, and parameter/map references.
+ *
+ * The grammar is header-only for maximum portability and uses X3's modern
+ * attribute propagation system to automatically build the AST during parsing.
  */
-typedef parse_tree_match_t::tree_iterator iter_t;
+namespace musrfit { namespace grammar
-
-//--------------------------------------------------------------------------
-/**
- * \brief EBNF-like grammar definition for parsing function entries in msr-file FUNCTION blocks.
- *
- * This grammar defines the syntax for parsing mathematical function expressions in msr-files.
- * It supports:
- * - Basic arithmetic operations (+, -, *, /)
- * - Mathematical functions (trigonometric, hyperbolic, logarithmic, exponential, etc.)
- * - Constants (PI, GAMMA_MU, field B, energy EN, temperature T)
- * - Parameters (PAR) and maps (MAP)
- * - Function references (FUN)
- *
- * The grammar follows an EBNF-like structure with the following hierarchy:
- * \verbatim
- * assignment   = fun_label '=' expression
- * expression   = term { ('+' | '-') term }
- * term         = factor { ('*' | '/') factor }
- * factor       = real | constant | parameter | map | function | power | '(' expression ')'
- * \endverbatim
- *
- * \see PFunction for the class that uses this grammar to evaluate parsed expressions
- */
-struct PFunctionGrammar : public grammar<PFunctionGrammar>
 {
-    static const int realID         = 1;  ///< Identifier for real number literals
+  using x3::int_;
-    static const int constPiID      = 2;  ///< Identifier for PI constant
+  using x3::double_;
-    static const int constGammaMuID = 3;  ///< Identifier for GAMMA_MU constant (muon gyromagnetic ratio)
+  using x3::lit;
-    static const int constFieldID   = 4;  ///< Identifier for magnetic field constant (B or -B)
+  using x3::lexeme;
-    static const int constEnergyID  = 5;  ///< Identifier for energy constant (EN or -EN)
+  using x3::attr;
-    static const int constTempID    = 6;  ///< Identifier for temperature constant (T# or -T#)
-    static const int funLabelID     = 7;  ///< Identifier for function label (FUN#)
-    static const int parameterID    = 8;  ///< Identifier for parameter reference (PAR# or -PAR#)
-    static const int mapID          = 9;  ///< Identifier for map reference (MAP#)
-    static const int functionID     = 10; ///< Identifier for mathematical functions (cos, sin, exp, etc.)
-    static const int powerID        = 11; ///< Identifier for power function (POW)
-    static const int factorID       = 12; ///< Identifier for factor in expression
-    static const int termID         = 13; ///< Identifier for term in expression
-    static const int expressionID   = 14; ///< Identifier for expression
-    static const int assignmentID   = 15; ///< Identifier for assignment statement
 
-    //------------------------------------------------------------------------
+  ///////////////////////////////////////////////////////////////////////////
-    /**
+  // Symbol tables - using inline to avoid multiple definition errors
-     * \brief Inner template structure defining the grammar rules.
+  ///////////////////////////////////////////////////////////////////////////
-     *
+
-     * This template structure contains the actual grammar rule definitions
+  /**
-     * using Boost.Spirit syntax. It defines how the parser should recognize
+   * @brief Symbol table for additive operators (+ and -).
-     * and build an abstract syntax tree (AST) for function expressions.
+   *
-     *
+   * Maps operator characters to their corresponding AST token types
-     * \tparam ScannerT Scanner type used by Boost.Spirit for parsing
+   * for addition and subtraction operations.
-     */
+   */
-    template <typename ScannerT>
+  struct additive_op_ : x3::symbols<ast::optoken>
-    struct definition
+  {
+    additive_op_()
     {
-        //--------------------------------------------------------------------
+      add("+", ast::op_plus)("-", ast::op_minus);
-        /**
+    }
-         * \brief Constructor that defines all grammar rules.
+  };
-         *
-         * Sets up the complete grammar hierarchy for parsing function expressions:
-         * - Terminals: real numbers, constants (PI, GAMMA_MU, B, EN, T), parameters (PAR), maps (MAP)
-         * - Functions: trigonometric (cos, sin, tan), hyperbolic (cosh, sinh, tanh),
-         *              inverse trigonometric (acos, asin, atan), inverse hyperbolic (acosh, asinh, atanh),
-         *              logarithmic (log, ln), exponential (exp), square root (sqrt), power (pow)
-         * - Operators: addition (+), subtraction (-), multiplication (*), division (/)
-         * - Expressions: Hierarchical structure following operator precedence
-         *
-         * \param self Reference to the enclosing PFunctionGrammar (unused but required by Boost.Spirit)
-         */
-        definition(PFunctionGrammar const& /*self*/)
-        {
-            //  Start grammar definition
-            real           =   leaf_node_d[ real_p ];
 
-            const_pi       =   leaf_node_d[ str_p("PI") ];
+  inline additive_op_ additive_op;  ///< Global instance of additive operator symbol table
 
-            const_gamma_mu =   leaf_node_d[ str_p("GAMMA_MU") ];
+  /**
+   * @brief Symbol table for multiplicative operators (* and /).
+   *
+   * Maps operator characters to their corresponding AST token types
+   * for multiplication and division operations.
+   */
+  struct multiplicative_op_ : x3::symbols<ast::optoken>
+  {
+    multiplicative_op_()
+    {
+      add("*", ast::op_times)("/", ast::op_divide);
+    }
+  };
 
-            const_field    =   leaf_node_d[ str_p("B") ] |
+  inline multiplicative_op_ multiplicative_op;  ///< Global instance of multiplicative operator symbol table
-                               leaf_node_d[ str_p("-B") ];
 
-            const_energy   =   leaf_node_d[ str_p("EN") ] |
+  /**
-                               leaf_node_d[ str_p("-EN") ];
+   * @brief Symbol table for mathematical function names.
+   *
+   * Maps uppercase function names (COS, SIN, EXP, etc.) to their
+   * corresponding AST function identifiers. Supports trigonometric,
+   * hyperbolic, inverse, exponential, and logarithmic functions.
+   */
+  struct fun_tok_ : x3::symbols<ast::funid>
+  {
+    fun_tok_()
+    {
+      add
+        ("COS",   ast::fun_cos)
+        ("SIN",   ast::fun_sin)
+        ("TAN",   ast::fun_tan)
+        ("COSH",  ast::fun_cosh)
+        ("SINH",  ast::fun_sinh)
+        ("TANH",  ast::fun_tanh)
+        ("ACOS",  ast::fun_acos)
+        ("ASIN",  ast::fun_asin)
+        ("ATAN",  ast::fun_atan)
+        ("ACOSH", ast::fun_acosh)
+        ("ASINH", ast::fun_asinh)
+        ("ATANH", ast::fun_atanh)
+        ("LOG",   ast::fun_log)
+        ("LN",    ast::fun_ln)
+        ("EXP",   ast::fun_exp)
+        ("SQRT",  ast::fun_sqrt);
+    }
+  };
 
-            const_temp    =    leaf_node_d[ ( lexeme_d[ "T" >> +digit_p ] ) ] |
+  inline fun_tok_ fun_tok;  ///< Global instance of function name symbol table
-                               leaf_node_d[ ( lexeme_d[ "-T" >> +digit_p ] ) ];
 
-            fun_label      =   leaf_node_d[ ( lexeme_d[ "FUN" >> +digit_p ] ) ];
+  /**
+   * @brief Symbol table for named constants.
+   *
+   * Maps constant names (PI, GAMMA_MU) to their corresponding
+   * AST constant type identifiers.
+   */
+  struct const_tok_ : x3::symbols<ast::constant::type>
+  {
+    const_tok_()
+    {
+      add("PI", ast::constant::pi)("GAMMA_MU", ast::constant::gamma_mu);
+    }
+  };
 
-            parameter      =   leaf_node_d[ ( lexeme_d[ "PAR" >> +digit_p ] ) |
+  inline const_tok_ const_tok;  ///< Global instance of constant name symbol table
-                                            ( lexeme_d[ "-PAR" >> +digit_p ] ) ];
 
-            map            =   leaf_node_d[ ( lexeme_d[ "MAP" >> +digit_p ] ) ];
+  ///////////////////////////////////////////////////////////////////////////
+  // Grammar Rules - Forward Declarations
+  ///////////////////////////////////////////////////////////////////////////
 
-            function       =   lexeme_d[ root_node_d[ str_p("COS")   ] >> ch_p('(') ] >> expression >> ch_p(')')
+  /// Top-level rule: FUN# = expression
-                           |   lexeme_d[ root_node_d[ str_p("SIN")   ] >> ch_p('(') ] >> expression >> ch_p(')')
+  x3::rule<class assignment, ast::assignment> const assignment = "assignment";
-                           |   lexeme_d[ root_node_d[ str_p("TAN")   ] >> ch_p('(') ] >> expression >> ch_p(')')
-                           |   lexeme_d[ root_node_d[ str_p("COSH")  ] >> ch_p('(') ] >> expression >> ch_p(')')
-                           |   lexeme_d[ root_node_d[ str_p("SINH")  ] >> ch_p('(') ] >> expression >> ch_p(')')
-                           |   lexeme_d[ root_node_d[ str_p("TANH")  ] >> ch_p('(') ] >> expression >> ch_p(')')
-                           |   lexeme_d[ root_node_d[ str_p("ACOS")  ] >> ch_p('(') ] >> expression >> ch_p(')')
-                           |   lexeme_d[ root_node_d[ str_p("ASIN")  ] >> ch_p('(') ] >> expression >> ch_p(')')
-                           |   lexeme_d[ root_node_d[ str_p("ATAN")  ] >> ch_p('(') ] >> expression >> ch_p(')')
-                           |   lexeme_d[ root_node_d[ str_p("ACOSH") ] >> ch_p('(') ] >> expression >> ch_p(')')
-                           |   lexeme_d[ root_node_d[ str_p("ASINH") ] >> ch_p('(') ] >> expression >> ch_p(')')
-                           |   lexeme_d[ root_node_d[ str_p("ATANH") ] >> ch_p('(') ] >> expression >> ch_p(')')
-                           |   lexeme_d[ root_node_d[ str_p("LOG")   ] >> ch_p('(') ] >> expression >> ch_p(')')
-                           |   lexeme_d[ root_node_d[ str_p("LN")    ] >> ch_p('(') ] >> expression >> ch_p(')')
-                           |   lexeme_d[ root_node_d[ str_p("EXP")   ] >> ch_p('(') ] >> expression >> ch_p(')')
-                           |   lexeme_d[ root_node_d[ str_p("SQRT")  ] >> ch_p('(') ] >> expression >> ch_p(')')
-                           ;
 
-            power          =   lexeme_d[ root_node_d[ str_p("POW")   ] >> ch_p('(') ] >> expression >> ch_p(',') >> expression >> ch_p(')')
+  /// Expression with addition/subtraction (lowest precedence)
-                           ;
+  x3::rule<class expression, ast::expression> const expression = "expression";
 
-            factor         =   real
+  /// Term with multiplication/division (higher precedence)
-                           |   const_pi
+  x3::rule<class term, ast::expression> const term = "term";
-                           |   const_gamma_mu
-                           |   const_field
-                           |   const_energy
-                           |   const_temp
-                           |   parameter
-                           |   map
-                           |   function
-                           |   power
-                           |   inner_node_d[ch_p('(') >> expression >> ch_p(')')]
-                           ;
 
-            term           =   factor >>
+  /// Factor: literal, constant, parameter, function, or parenthesized expression (highest precedence)
-                               *(  (root_node_d[ch_p('*')] >> factor)
+  x3::rule<class factor, ast::operand> const factor = "factor";
-                                 | (root_node_d[ch_p('/')] >> factor)
-                               );
 
-            expression     =   term >>
+  /// Constant: PI, GAMMA_MU, B, EN, or T#
-                               *(  (root_node_d[ch_p('+')] >> term)
+  x3::rule<class constant, ast::constant> const constant = "constant";
-                                 | (root_node_d[ch_p('-')] >> term)
-                               );
 
-            assignment     =   (fun_label >> ch_p('=') >> expression);
+  /// Parameter reference: PAR# or -PAR#
-            //  End grammar definition
+  x3::rule<class parameter, ast::parameter> const parameter = "parameter";
 
-            // turn on the debugging info.
+  /// Map reference: MAP# or -MAP#
-            BOOST_SPIRIT_DEBUG_RULE(real);
+  x3::rule<class map_ref, ast::map_ref> const map = "map";
-            BOOST_SPIRIT_DEBUG_RULE(const_pi);
-            BOOST_SPIRIT_DEBUG_RULE(const_gamma_mu);
-            BOOST_SPIRIT_DEBUG_RULE(const_field);
-            BOOST_SPIRIT_DEBUG_RULE(const_energy);
-            BOOST_SPIRIT_DEBUG_RULE(const_temp);
-            BOOST_SPIRIT_DEBUG_RULE(fun_label);
-            BOOST_SPIRIT_DEBUG_RULE(parameter);
-            BOOST_SPIRIT_DEBUG_RULE(map);
-            BOOST_SPIRIT_DEBUG_RULE(function);
-            BOOST_SPIRIT_DEBUG_RULE(power);
-            BOOST_SPIRIT_DEBUG_RULE(factor);
-            BOOST_SPIRIT_DEBUG_RULE(term);
-            BOOST_SPIRIT_DEBUG_RULE(expression);
-            BOOST_SPIRIT_DEBUG_RULE(assignment);
-        }
 
-        rule<ScannerT, parser_context<>, parser_tag<assignmentID> >   assignment;    ///< Rule for assignment: FUN# = expression
+  /// Function call: FUNC(expression)
-        rule<ScannerT, parser_context<>, parser_tag<expressionID> >   expression;    ///< Rule for expression: term { ('+' | '-') term }
+  x3::rule<class function_call, ast::function_call> const function = "function";
-        rule<ScannerT, parser_context<>, parser_tag<termID> >         term;          ///< Rule for term: factor { ('*' | '/') factor }
-        rule<ScannerT, parser_context<>, parser_tag<factorID> >       factor;        ///< Rule for factor: operand or parenthesized expression
-        rule<ScannerT, parser_context<>, parser_tag<functionID> >     function;      ///< Rule for mathematical functions
-        rule<ScannerT, parser_context<>, parser_tag<powerID> >        power;         ///< Rule for power function POW(base, exponent)
-        rule<ScannerT, parser_context<>, parser_tag<mapID> >          map;           ///< Rule for map reference MAP#
-        rule<ScannerT, parser_context<>, parser_tag<parameterID> >    parameter;     ///< Rule for parameter reference PAR# or -PAR#
-        rule<ScannerT, parser_context<>, parser_tag<funLabelID> >     fun_label;     ///< Rule for function label FUN#
-        rule<ScannerT, parser_context<>, parser_tag<constTempID> >    const_temp;    ///< Rule for temperature constant T# or -T#
-        rule<ScannerT, parser_context<>, parser_tag<constEnergyID> >  const_energy;  ///< Rule for energy constant EN or -EN
-        rule<ScannerT, parser_context<>, parser_tag<constFieldID> >   const_field;   ///< Rule for field constant B or -B
-        rule<ScannerT, parser_context<>, parser_tag<constGammaMuID> > const_gamma_mu;///< Rule for muon gyromagnetic ratio constant
-        rule<ScannerT, parser_context<>, parser_tag<constPiID> >      const_pi;      ///< Rule for PI constant
-        rule<ScannerT, parser_context<>, parser_tag<realID> >         real;          ///< Rule for real number literals
 
-        //--------------------------------------------------------------------
+  /// Power operation: POW(base, exponent)
-        /**
+  x3::rule<class power_call, ast::power_call> const power = "power";
-         * \brief Returns the starting rule for the grammar.
+
-         *
+  ///////////////////////////////////////////////////////////////////////////
-         * The parser begins by matching the assignment rule, which represents
+  // Grammar Rule Definitions
-         * a complete function definition (e.g., FUN1 = PAR1 * cos(PAR2 * PI)).
+  ///////////////////////////////////////////////////////////////////////////
-         *
+
-         * \return Reference to the assignment rule as the grammar entry point
+  /**
-         */
+   * @brief Assignment rule: FUN# = expression
-        rule<ScannerT, parser_context<>, parser_tag<assignmentID> > const&
+   *
-        start() const { return assignment; }
+   * Parses a function assignment statement, extracting the function number
-    };
+   * and the expression to evaluate.
-};
+   */
+  auto const assignment_def =
+      lit("FUN") >> int_ >> '=' >> expression;
+
+  /**
+   * @brief Expression rule: term ((+|-) term)*
+   *
+   * Handles addition and subtraction with left-associative evaluation.
+   * Lower precedence than multiplication/division.
+   */
+  auto const expression_def =
+      term >> *(additive_op >> term);
+
+  /**
+   * @brief Term rule: factor ((*|/) factor)*
+   *
+   * Handles multiplication and division with left-associative evaluation.
+   * Higher precedence than addition/subtraction.
+   */
+  auto const term_def =
+      factor >> *(multiplicative_op >> factor);
+
+  /**
+   * @brief Factor rule: the atomic elements of expressions.
+   *
+   * Matches numeric literals, constants, parameters, maps, function calls,
+   * power operations, or parenthesized sub-expressions. Parentheses allow
+   * overriding operator precedence.
+   */
+  auto const factor_def =
+      double_
+      | constant
+      | parameter
+      | map
+      | function
+      | power
+      | ('(' >> expression >> ')');
+
+  /**
+   * @brief Constant rule: PI | GAMMA_MU | B | -B | EN | -EN | T# | -T#
+   *
+   * Parses symbolic constants, optionally with negation. Temperature
+   * constants include an index number (T0, T1, T2, etc.).
+   */
+  auto const constant_def =
+      (const_tok >> attr(false) >> attr(0))
+      | (lit("B")  >> attr(ast::constant::field)  >> attr(false) >> attr(0))
+      | (lit("-B") >> attr(ast::constant::field)  >> attr(true)  >> attr(0))
+      | (lit("EN")  >> attr(ast::constant::energy) >> attr(false) >> attr(0))
+      | (lit("-EN") >> attr(ast::constant::energy) >> attr(true)  >> attr(0))
+      | (lit('T')  >> attr(ast::constant::temp) >> attr(false) >> int_)
+      | (lit("-T") >> attr(ast::constant::temp) >> attr(true)  >> int_);
+
+  /**
+   * @brief Parameter rule: PAR# | -PAR#
+   *
+   * Parses parameter references with 1-based indexing. The lexeme directive
+   * for -PAR# ensures the minus sign is treated as part of the token,
+   * not as a separate operator.
+   */
+  auto const parameter_def =
+      (lexeme[lit("-PAR") >> int_] >> attr(true))
+      | (lit("PAR") >> int_ >> attr(false));
+
+  /**
+   * @brief Map rule: MAP# | -MAP#
+   *
+   * Parses map references for indirect parameter lookup with 1-based indexing.
+   * The lexeme directive for -MAP# ensures the minus sign is part of the token.
+   */
+  auto const map_def =
+      (lexeme[lit("-MAP") >> int_] >> attr(true))
+      | (lit("MAP") >> int_ >> attr(false));
+
+  /**
+   * @brief Function rule: FUNC(expression)
+   *
+   * Parses mathematical function calls. The function name is matched by
+   * fun_tok and the argument is a full expression.
+   */
+  auto const function_def =
+      fun_tok >> '(' >> expression >> ')';
+
+  /**
+   * @brief Power rule: POW(base, exponent)
+   *
+   * Parses power operations with two expression arguments separated by comma.
+   * Both base and exponent can be arbitrary expressions.
+   */
+  auto const power_def =
+      lit("POW") >> '(' >> expression >> ',' >> expression >> ')';
+
+  /**
+   * @brief Links rule names to their definitions.
+   *
+   * Required by Boost.Spirit X3 to connect the forward-declared rules
+   * with their actual parsing logic.
+   */
+  BOOST_SPIRIT_DEFINE(
+    assignment,
+    expression,
+    term,
+    factor,
+    constant,
+    parameter,
+    map,
+    function,
+    power
+  )
+
+}}
+
+/**
+ * @namespace musrfit
+ * @brief Top-level namespace for musrfit components.
+ */
+namespace musrfit {
+  /**
+   * @brief Provides access to the top-level grammar rule.
+   *
+   * Returns a reference to the assignment rule, which is the entry point
+   * for parsing complete function assignment statements (FUN# = expression).
+   * Use this function to obtain the grammar for parsing with Spirit X3.
+   *
+   * @return Constant reference to the assignment grammar rule
+   *
+   * @code
+   * auto const& grammar = musrfit::function_grammar();
+   * bool success = x3::phrase_parse(iter, end, grammar, x3::space, result);
+   * @endcode
+   */
+  inline auto const& function_grammar()
+  {
+    return grammar::assignment;
+  }
+}
 
 #endif // _PFUNCTIONGRAMMAR_H_

src/musredit_qt6/mupp/var/include/PAnnotation.hpp

@@ -51,7 +51,7 @@ namespace mupp
    * handler to pinpoint the exact location of errors in the source text.
    *
    * The annotation is performed after successful parsing but before semantic
-   * analysis, using Boost.Phoenix function objects integrated with the parser.
+   * analysis, integrated with the Spirit X3 parser.
    *
    * @tparam Iterator the iterator type for traversing the source code (typically std::string::const_iterator)
    */
@@ -59,9 +59,6 @@ namespace mupp
   template <typename Iterator>
   struct PAnnotation
   {
-    /// Result type specification required by Boost.Phoenix function protocol
-    template <typename, typename>
-    struct result { typedef void type; };
 
     std::vector<Iterator>& iters; ///< Reference to vector storing iterator positions indexed by AST node IDs
 
@@ -79,8 +76,6 @@ namespace mupp
      */
     struct set_id
     {
-      typedef void result_type; ///< Return type for Boost.Phoenix compatibility
-
       int id; ///< The ID to assign to tagged AST nodes
 
       /**

src/musredit_qt6/mupp/var/include/PErrorHandler.hpp

@@ -46,7 +46,7 @@ namespace mupp
    *
    * This error handler logs detailed error information to a file, including
    * the error message, line number, source line, and a visual pointer to the
-   * error position. It integrates with the Boost.Spirit parser error handling
+   * error position. It integrates with the Boost.Spirit X3 parser error handling
    * mechanism and works in conjunction with the PAnnotation handler to map
    * AST node IDs back to source positions.
    *
@@ -58,9 +58,6 @@ namespace mupp
   template <typename Iterator>
   struct PErrorHandler
   {
-     /// Result type specification required by Boost.Phoenix function protocol
-     template <typename, typename, typename>
-     struct result { typedef void type; };
 
      /**
       * @brief Constructor that stores the source code range.

src/musredit_qt6/mupp/var/include/PExpression.hpp

@@ -33,21 +33,12 @@
 #ifndef _PEXPRESSION_HPP_
 #define _PEXPRESSION_HPP_
 
-///////////////////////////////////////////////////////////////////////////////
-// Spirit v2.5 allows you to suppress automatic generation
-// of predefined terminals to speed up complation. With
-// BOOST_SPIRIT_NO_PREDEFINED_TERMINALS defined, you are
-// responsible in creating instances of the terminals that
-// you need (e.g. see qi::uint_type uint_ below).
-#define BOOST_SPIRIT_NO_PREDEFINED_TERMINALS
-///////////////////////////////////////////////////////////////////////////////
-
 ///////////////////////////////////////////////////////////////////////////////
 // Uncomment this if you want to enable debugging
-// #define BOOST_SPIRIT_QI_DEBUG
+// #define BOOST_SPIRIT_X3_DEBUG
 ///////////////////////////////////////////////////////////////////////////////
 
-#include <boost/spirit/include/qi.hpp>
+#include <boost/spirit/home/x3.hpp>
 #include "PAst.hpp"
 #include "PErrorHandler.hpp"
 #include "PSkipper.hpp"
@@ -55,14 +46,14 @@
 
 namespace mupp { namespace parser
 {
-    namespace qi = boost::spirit::qi;
+    namespace x3 = boost::spirit::x3;
-    namespace ascii = boost::spirit::ascii;
+    namespace ascii = boost::spirit::x3::ascii;
 
     ///////////////////////////////////////////////////////////////////////////////
     /**
      * @brief The PExpression grammar for parsing mathematical expressions.
      *
-     * This Boost.Spirit grammar defines the syntax for parsing arithmetic
+     * This Boost.Spirit X3 grammar defines the syntax for parsing arithmetic
      * expressions with proper operator precedence and associativity:
      * - Primary expressions: numbers, variables, functions, parenthesized expressions
      * - Unary operators: +, - (highest precedence)
@@ -80,31 +71,27 @@ namespace mupp { namespace parser
      * - 3.14 * $radius
      * - sin($theta) + cos($phi)
      * - pow($x, 2.0) + pow($y, 2.0)
-     *
-     * @tparam Iterator the iterator type for the input (typically std::string::const_iterator)
      */
     ///////////////////////////////////////////////////////////////////////////////
-    template <typename Iterator>
-    struct PExpression : qi::grammar<Iterator, ast::expression(), PSkipper<Iterator> >
-    {
-        /**
-         * @brief Constructor that initializes the grammar rules.
-         * @param error_handler reference to the error handler for reporting parse errors
-         */
-        PExpression(PErrorHandler<Iterator>& error_handler);
 
-        qi::symbols<char, ast::optoken> additive_op;        ///< Symbol table for additive operators (+, -)
+    // Rule IDs
-        qi::symbols<char, ast::optoken> multiplicative_op;  ///< Symbol table for multiplicative operators (*, /)
+    struct expr_class;
-        qi::symbols<char, ast::optoken> unary_op;           ///< Symbol table for unary operators (+, -)
+    struct additive_expr_class;
-        qi::symbols<char, ast::funid> fun_tok;              ///< Symbol table for function names
+    struct multiplicative_expr_class;
+    struct unary_expr_class;
+    struct primary_expr_class;
+    struct identifier_class;
 
-        qi::rule<Iterator, ast::expression(), PSkipper<Iterator> > expr;                ///< Top-level expression rule
+    // Rule declarations
-        qi::rule<Iterator, ast::expression(), PSkipper<Iterator> > additive_expr;       ///< Additive expression rule (lowest precedence)
+    typedef x3::rule<expr_class, ast::expression> expr_type;
-        qi::rule<Iterator, ast::expression(), PSkipper<Iterator> > multiplicative_expr; ///< Multiplicative expression rule (medium precedence)
+    typedef x3::rule<additive_expr_class, ast::expression> additive_expr_type;
-        qi::rule<Iterator, ast::operand(), PSkipper<Iterator> > unary_expr;             ///< Unary expression rule
+    typedef x3::rule<multiplicative_expr_class, ast::expression> multiplicative_expr_type;
-        qi::rule<Iterator, ast::operand(), PSkipper<Iterator> > primary_expr;           ///< Primary expression rule (highest precedence)
+    typedef x3::rule<unary_expr_class, ast::operand> unary_expr_type;
-        qi::rule<Iterator, std::string(), PSkipper<Iterator> > identifier;              ///< Identifier rule (variables prefixed with '$')
+    typedef x3::rule<primary_expr_class, ast::operand> primary_expr_type;
-    };
+    typedef x3::rule<identifier_class, std::string> identifier_type;
+
+    BOOST_SPIRIT_DECLARE(expr_type, additive_expr_type, multiplicative_expr_type,
+                         unary_expr_type, primary_expr_type, identifier_type)
 }}
 
 #endif // _PEXPRESSION_HPP_

src/musredit_qt6/mupp/var/include/PExpressionDef.hpp

@@ -9,8 +9,8 @@
   see https://github.com/boostorg/spirit
 
   This file contains the implementation (definition) of the PExpression
-  template grammar. It defines the actual grammar rules and their semantic
+  grammar. It defines the actual grammar rules and their semantic
-  actions using Boost.Spirit Qi.
+  actions using Boost.Spirit X3.
 
   The grammar implements expression parsing with proper operator precedence:
   - Primary expressions (literals, variables, functions)
@@ -46,93 +46,116 @@
 #include "PExpression.hpp"
 #include "PErrorHandler.hpp"
 #include "PAnnotation.hpp"
-#include <boost/phoenix/function.hpp>
 
 namespace mupp { namespace parser
 {
-  template <typename Iterator>
+    namespace x3 = boost::spirit::x3;
-  PExpression<Iterator>::PExpression(PErrorHandler<Iterator>& error_handler)
+    namespace ascii = boost::spirit::x3::ascii;
-      : PExpression::base_type(expr)
-  {
-    qi::_1_type _1;
-    qi::_2_type _2;
-    qi::_3_type _3;
-    qi::_4_type _4;
 
-    qi::char_type char_;
+    using x3::char_;
-    qi::double_type double_;
+    using x3::double_;
-    qi::_val_type _val;
+    using x3::raw;
-    qi::raw_type raw;
+    using x3::lexeme;
-    qi::lexeme_type lexeme;
+    using ascii::alpha;
-    qi::alpha_type alpha;
+    using ascii::alnum;
-    qi::alnum_type alnum;
-
-    using qi::on_error;
-    using qi::on_success;
-    using qi::fail;
-    using boost::phoenix::function;
-
-    typedef function<mupp::PErrorHandler<Iterator> > error_handler_function;
-    typedef function<mupp::PAnnotation<Iterator> > annotation_function;
 
     ///////////////////////////////////////////////////////////////////////
-    // Tokens
+    // Symbol tables for operators and functions
-    additive_op.add
+    ///////////////////////////////////////////////////////////////////////
-        ("+", ast::op_plus)
-        ("-", ast::op_minus)
-        ;
 
-    multiplicative_op.add
+    inline struct additive_op_ : x3::symbols<ast::optoken>
-        ("*", ast::op_times)
+    {
-        ("/", ast::op_divide)
+        additive_op_()
-        ;
+        {
+            add
+                ("+", ast::op_plus)
+                ("-", ast::op_minus)
+                ;
+        }
+    } additive_op;
 
-    unary_op.add
+    inline struct multiplicative_op_ : x3::symbols<ast::optoken>
-        ("+", ast::op_positive)
+    {
-        ("-", ast::op_negative)
+        multiplicative_op_()
-        ;
+        {
+            add
+                ("*", ast::op_times)
+                ("/", ast::op_divide)
+                ;
+        }
+    } multiplicative_op;
 
-    fun_tok.add
+    inline struct unary_op_ : x3::symbols<ast::optoken>
-        ("max", ast::fun_max)
+    {
-        ("min", ast::fun_min)
+        unary_op_()
-        ("abs", ast::fun_abs)
+        {
-        ("sin", ast::fun_sin)
+            add
-        ("cos", ast::fun_cos)
+                ("+", ast::op_positive)
-        ("tan", ast::fun_tan)
+                ("-", ast::op_negative)
-        ("sinh", ast::fun_sinh)
+                ;
-        ("cosh", ast::fun_cosh)
+        }
-        ("tanh", ast::fun_tanh)
+    } unary_op;
-        ("asin", ast::fun_asin)
+
-        ("acos", ast::fun_acos)
+    inline struct fun_tok_ : x3::symbols<ast::funid>
-        ("atan", ast::fun_atan)
+    {
-        ("exp", ast::fun_exp)
+        fun_tok_()
-        ("log", ast::fun_log)
+        {
-        ("ln",  ast::fun_ln)
+            add
-        ("sqrt", ast::fun_sqrt)
+                ("max", ast::fun_max)
-        ;
+                ("min", ast::fun_min)
+                ("abs", ast::fun_abs)
+                ("sin", ast::fun_sin)
+                ("cos", ast::fun_cos)
+                ("tan", ast::fun_tan)
+                ("sinh", ast::fun_sinh)
+                ("cosh", ast::fun_cosh)
+                ("tanh", ast::fun_tanh)
+                ("asin", ast::fun_asin)
+                ("acos", ast::fun_acos)
+                ("atan", ast::fun_atan)
+                ("exp", ast::fun_exp)
+                ("log", ast::fun_log)
+                ("ln",  ast::fun_ln)
+                ("sqrt", ast::fun_sqrt)
+                ;
+        }
+    } fun_tok;
+
+    ///////////////////////////////////////////////////////////////////////
+    // Rule definitions
+    ///////////////////////////////////////////////////////////////////////
+
+    inline expr_type const expr = "expr";
+    inline additive_expr_type const additive_expr = "additive_expr";
+    inline multiplicative_expr_type const multiplicative_expr = "multiplicative_expr";
+    inline unary_expr_type const unary_expr = "unary_expr";
+    inline primary_expr_type const primary_expr = "primary_expr";
+    inline identifier_type const identifier = "identifier";
 
     ///////////////////////////////////////////////////////////////////////
     // Grammar
-    expr =
+    ///////////////////////////////////////////////////////////////////////
-        additive_expr.alias()
+
+    inline auto const expr_def =
+        additive_expr
         ;
 
-    additive_expr =
+    inline auto const additive_expr_def =
         multiplicative_expr
         >> *(additive_op > multiplicative_expr)
-           ;
+        ;
 
-    multiplicative_expr =
+    inline auto const multiplicative_expr_def =
         unary_expr
         >> *(multiplicative_op > unary_expr)
-           ;
+        ;
 
-    unary_expr =
+    inline auto const unary_expr_def =
         primary_expr
         |   (unary_op > primary_expr)
         ;
 
-    primary_expr =
+    inline auto const primary_expr_def =
         double_
         |   identifier
         |   fun_tok > '(' > expr > ')'
@@ -140,36 +163,13 @@ namespace mupp { namespace parser
         |   '(' > expr > ')'
         ;
 
-    identifier =
+    inline auto const identifier_def =
         raw[lexeme['$' >> *(alnum | '_')]]
         ;
 
-    // name all the rules
+    BOOST_SPIRIT_DEFINE(expr, additive_expr, multiplicative_expr,
-    additive_expr.name("additive_expr");
+                        unary_expr, primary_expr, identifier)
-    multiplicative_expr.name("multiplicative_expr");
-    unary_expr.name("unary_expr");
-    primary_expr.name("primary_expr");
-    identifier.name("identifier");
 
-    // Debugging and error handling and reporting support.
-    BOOST_SPIRIT_DEBUG_NODES(
-      (expr)
-      (additive_expr)
-      (multiplicative_expr)
-      (unary_expr)
-      (primary_expr)
-      (identifier)
-     );
-
-    // Error handling: on error in expr, call error_handler.
-    on_error<fail>(expr,
-         error_handler_function(error_handler)(
-         "**ERROR** Expecting ", _4, _3));
-
-    // Annotation: on success in primary_expr, call annotation.
-    on_success(primary_expr,
-         annotation_function(error_handler.iters)(_val, _1));
-  }
 }}
 
 

src/musredit_qt6/mupp/var/include/PSkipper.hpp

@@ -33,12 +33,12 @@
 #ifndef _PSKIPPER_HPP_
 #define _PSKIPPER_HPP_
 
-#include <boost/spirit/include/qi.hpp>
+#include <boost/spirit/home/x3.hpp>
 
 namespace mupp { namespace parser
 {
-    namespace qi = boost::spirit::qi;
+    namespace x3 = boost::spirit::x3;
-    namespace ascii = boost::spirit::ascii;
+    namespace ascii = boost::spirit::x3::ascii;
 
     ///////////////////////////////////////////////////////////////////////////////
     /**
@@ -61,38 +61,22 @@ namespace mupp { namespace parser
      * / * This is a
      *    multi-line comment * /
      * @endcode
-     *
-     * @tparam Iterator the iterator type for the input (typically std::string::const_iterator)
      */
     ///////////////////////////////////////////////////////////////////////////////
-    template <typename Iterator>
-    struct PSkipper : qi::grammar<Iterator>
-    {
-        /**
-         * @brief Constructor that initializes the skipper grammar rules.
-         *
-         * Sets up the grammar to recognize whitespace and various comment styles.
-         */
-        PSkipper() : PSkipper::base_type(start)
-        {
-            qi::char_type char_;
-            qi::lit_type lit;
-            qi::eol_type eol;
-            ascii::space_type space;
-            ascii::print_type print;
 
-            single_line_comment = (lit('%') | lit('#') | lit("//")) >> *print >> eol;
+    using x3::char_;
+    using x3::lit;
+    using x3::eol;
+    using ascii::space;
+    using ascii::print;
 
-            start =
+    inline auto const single_line_comment = (lit('%') | lit('#') | lit("//")) >> *print >> eol;
-                    space                               // tab/space/cr/lf
-                |   "/*" >> *(char_ - "*/") >> "*/"     // C-style comments
-                |   single_line_comment
-                ;
-        }
 
-        qi::rule<Iterator> single_line_comment; ///< Rule for single-line comments (%, #, //)
+    inline auto const skipper =
-        qi::rule<Iterator> start;               ///< Top-level skipper rule
+            space                               // tab/space/cr/lf
-    };
+        |   "/*" >> *(char_ - "*/") >> "*/"     // C-style comments
+        |   single_line_comment
+        ;
 }}
 
 #endif // _PSKIPPER_HPP_

src/musredit_qt6/mupp/var/include/PStatement.hpp

@@ -59,25 +59,23 @@ namespace mupp { namespace parser
    *
    * The grammar parses a statement list (one or more statements) and builds
    * an AST that can be analyzed and evaluated by the semantic analyzer.
-   *
-   * @tparam Iterator the iterator type for the input (typically std::string::const_iterator)
    */
   ///////////////////////////////////////////////////////////////////////////////
-  template <typename Iterator>
-  struct PStatement : qi::grammar<Iterator, ast::statement_list(), PSkipper<Iterator> >
-  {
-    /**
-     * @brief Constructor that initializes the statement grammar rules.
-     * @param error_handler reference to the error handler for reporting parse errors
-     */
-    PStatement(PErrorHandler<Iterator>& error_handler);
 
-    PExpression<Iterator> expr;                                                      ///< Expression grammar for parsing right-hand sides
+  // Rule IDs
-    qi::rule<Iterator, ast::statement_list(), PSkipper<Iterator> > statement_list;   ///< Rule for parsing a list of statements
+  struct statement_list_class;
-    qi::rule<Iterator, ast::variable_declaration(), PSkipper<Iterator> > variable_declaration; ///< Rule for variable declarations
+  struct variable_declaration_class;
-    qi::rule<Iterator, ast::assignment(), PSkipper<Iterator> > assignment;           ///< Rule for assignment statements
+  struct assignment_class;
-    qi::rule<Iterator, std::string(), PSkipper<Iterator> > identifier;               ///< Rule for identifiers (without '$' prefix)
+  struct stmt_identifier_class;
-  };
+
+  // Rule declarations
+  typedef x3::rule<statement_list_class, ast::statement_list> statement_list_type;
+  typedef x3::rule<variable_declaration_class, ast::variable_declaration> variable_declaration_type;
+  typedef x3::rule<assignment_class, ast::assignment> assignment_type;
+  typedef x3::rule<stmt_identifier_class, std::string> stmt_identifier_type;
+
+  BOOST_SPIRIT_DECLARE(statement_list_type, variable_declaration_type,
+                       assignment_type, stmt_identifier_type)
 }}
 
 #endif // _PSTATEMENT_HPP_

src/musredit_qt6/mupp/var/include/PStatementDef.hpp

@@ -9,8 +9,8 @@
   see https://github.com/boostorg/spirit
 
   This file contains the implementation (definition) of the PStatement
-  template grammar. It defines the grammar rules for parsing variable
+  grammar. It defines the grammar rules for parsing variable
-  declarations and assignments using Boost.Spirit Qi.
+  declarations and assignments using Boost.Spirit X3.
 
   The grammar supports:
   - Variable declarations: var <identifier> = <expression>
@@ -43,77 +43,55 @@
  ***************************************************************************/
 
 #include "PStatement.hpp"
+#include "PExpressionDef.hpp"
 #include "PErrorHandler.hpp"
 #include "PAnnotation.hpp"
 
 namespace mupp { namespace parser
 {
-  template <typename Iterator>
+    namespace x3 = boost::spirit::x3;
-  PStatement<Iterator>::PStatement(PErrorHandler<Iterator>& error_handler)
+    namespace ascii = boost::spirit::x3::ascii;
-      : PStatement::base_type(statement_list), expr(error_handler)
-  {
-    qi::_1_type _1;
-    qi::_2_type _2;
-    qi::_3_type _3;
-    qi::_4_type _4;
 
-    qi::_val_type _val;
+    using x3::raw;
-    qi::raw_type raw;
+    using x3::lexeme;
-    qi::lexeme_type lexeme;
+    using ascii::alpha;
-    qi::alpha_type alpha;
+    using ascii::alnum;
-    qi::alnum_type alnum;
 
-    using qi::on_error;
+    ///////////////////////////////////////////////////////////////////////
-    using qi::on_success;
+    // Rule definitions
-    using qi::fail;
+    ///////////////////////////////////////////////////////////////////////
-    using boost::phoenix::function;
 
-    typedef function<mupp::PErrorHandler<Iterator> > error_handler_function;
+    inline statement_list_type const statement_list = "statement_list";
-    typedef function<mupp::PAnnotation<Iterator> > annotation_function;
+    inline variable_declaration_type const variable_declaration = "variable_declaration";
+    inline assignment_type const assignment = "assignment";
+    inline stmt_identifier_type const stmt_identifier = "identifier";
 
-    statement_list =
+    ///////////////////////////////////////////////////////////////////////
+    // Grammar
+    ///////////////////////////////////////////////////////////////////////
+
+    inline auto const statement_list_def =
         +(variable_declaration | assignment)
         ;
 
-    identifier =
+    inline auto const stmt_identifier_def =
         raw[lexeme[(alpha | '_') >> *(alnum | '_')]]
         ;
 
-    variable_declaration =
+    inline auto const variable_declaration_def =
         lexeme["var" >> !(alnum | '_')] // make sure we have whole words
-        >   identifier
+        >   stmt_identifier
         >   -('=' > expr)
         ;
 
-    assignment =
+    inline auto const assignment_def =
-        identifier
+        stmt_identifier
         >   '='
         >   expr
         ;
 
-    // name all the rules
+    BOOST_SPIRIT_DEFINE(statement_list, variable_declaration, assignment, stmt_identifier)
-    statement_list.name("statement_list");
-    identifier.name("identifier");
-    variable_declaration.name("variable_declaration");
-    assignment.name("assignment");
 
-    // Debugging and error handling and reporting support.
-    BOOST_SPIRIT_DEBUG_NODES(
-      (statement_list)
-      (identifier)
-      (variable_declaration)
-      (assignment)
-    );
-
-    // Error handling: on error in statement_list, call error_handler.
-    on_error<fail>(statement_list,
-       error_handler_function(error_handler)(
-       "**ERROR** Expecting ", _4, _3));
-
-    // Annotation: on success in assignment, call annotation.
-    on_success(assignment,
-       annotation_function(error_handler.iters)(_val, _1));
-  }
 }}
 
 

src/musredit_qt6/mupp/var/src/PExpression.cpp

@@ -8,8 +8,8 @@
   Based on Joel de Guzman example on calc7,
   see https://github.com/boostorg/spirit
 
-  This file explicitly instantiates the PExpression template grammar for
+  This file instantiates the PExpression grammar rules for
-  std::string::const_iterator. Template instantiation in a separate
+  std::string::const_iterator. Instantiation in a separate
   compilation unit reduces compile times and allows the grammar
   implementation to be hidden from clients.
 
@@ -35,11 +35,4 @@
  *   59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.             *
  ***************************************************************************/
 
-#if defined(_MSC_VER)
-# pragma warning(disable: 4345)
-#endif
-
 #include "PExpressionDef.hpp"
-
-typedef std::string::const_iterator iterator_type;
-template struct mupp::parser::PExpression<iterator_type>;

src/musredit_qt6/mupp/var/src/PStatement.cpp

@@ -8,8 +8,8 @@
   Based on Joel de Guzman example on calc7,
   see https://github.com/boostorg/spirit
 
-  This file explicitly instantiates the PStatement template grammar for
+  This file instantiates the PStatement grammar rules for
-  std::string::const_iterator. Template instantiation in a separate
+  std::string::const_iterator. Instantiation in a separate
   compilation unit reduces compile times and allows the grammar
   implementation to be hidden from clients.
 
@@ -35,11 +35,4 @@
  *   59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.             *
  ***************************************************************************/
 
-#if defined(_MSC_VER)
-# pragma warning(disable: 4345)
-#endif
-
 #include "PStatementDef.hpp"
-
-typedef std::string::const_iterator iterator_type;
-template struct mupp::parser::PStatement<iterator_type>;

src/musredit_qt6/mupp/var/src/PVarHandler.cpp

@@ -34,8 +34,11 @@
 #include "PSkipper.hpp"
 #include "PErrorHandler.hpp"
 #include "PStatement.hpp"
+#include "PStatementDef.hpp"
 #include "PProgram.hpp"
 
+#include <boost/spirit/home/x3.hpp>
+
 //--------------------------------------------------------------------------
 /**
  * @brief Default constructor creating an invalid handler.
@@ -78,12 +81,11 @@ PVarHandler::PVarHandler(PmuppCollection *coll, std::string parse_str, std::stri
   iterator_type end = fParseStr.end();
 
   mupp::PErrorHandler<iterator_type> error_handler(iter, end);   // the error handler
-  mupp::parser::PStatement<iterator_type> parser(error_handler); // the parser
   mupp::prog::PProgram prog(error_handler); // our compiler, and exec
-  mupp::parser::PSkipper<iterator_type> skipper; // the skipper parser
 
   // perform the parsing
-  bool success = phrase_parse(iter, end, parser, skipper, fAst);
+  namespace x3 = boost::spirit::x3;
+  bool success = x3::phrase_parse(iter, end, mupp::parser::statement_list, mupp::parser::skipper, fAst);
   if (success && iter == end) {
     if (prog(fAst)) { // semantic analysis
       std::vector<double> data, dataErr;

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.
+       * @brief Evaluates a leer/empty AST node.
-       * @param AST nil node (unused)
+       * @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