src/scriptvm/common.h

/*
 * Copyright (c) 2014-2016 Christian Schoenebeck
 *
 * http://www.linuxsampler.org
 *
 * This file is part of LinuxSampler and released under the same terms.
 * See README file for details.
 */

// This header defines data types shared between the VM core implementation
// (inside the current source directory) and other parts of the sampler
// (located at other source directories).

#ifndef LS_INSTR_SCRIPT_PARSER_COMMON_H
#define LS_INSTR_SCRIPT_PARSER_COMMON_H

#include "../common/global.h"
#include <vector>
#include <map>
#include <stddef.h> // offsetof()

namespace LinuxSampler {

    /**
     * Identifies the type of a noteworthy issue identified by the script
     * parser. That's either a parser error or parser warning.
     */
    enum ParserIssueType_t {
        PARSER_ERROR, ///< Script parser encountered an error, the script cannot be executed.
        PARSER_WARNING ///< Script parser encountered a warning, the script may be executed if desired, but the script may not necessarily behave as originally intended by the script author.
    };

    /** @brief Expression's data type.
     *
     * Identifies to which data type an expression within a script evaluates to.
     * This can for example reflect the data type of script function arguments,
     * script function return values, but also the resulting data type of some
     * mathematical formula within a script.
     */
    enum ExprType_t {
        EMPTY_EXPR, ///< i.e. on invalid expressions or i.e. a function call that does not return a result value (the built-in wait() or message() functions for instance)
        INT_EXPR, ///< integer (scalar) expression
        INT_ARR_EXPR, ///< integer array expression
        STRING_EXPR, ///< string expression
        STRING_ARR_EXPR, ///< string array expression
    };

    /** @brief Result flags of a script statement or script function call.
     *
     * A set of bit flags which provide informations about the success or
     * failure of a statement within a script. That's also especially used for
     * providing informations about success / failure of a call to a built-in
     * script function. The virtual machine evaluates these flags during runtime
     * to decide whether it should i.e. stop or suspend execution of a script.
     *
     * Since these are bit flags, these constants are bitwise combined.
     */
    enum StmtFlags_t {
       STMT_SUCCESS = 0, ///< Function / statement was executed successfully, no error occurred.
       STMT_ABORT_SIGNALLED = 1, ///< VM should stop the current callback execution (usually because of an error, but might also be without an error reason, i.e. when the built-in script function exit() was called).
       STMT_SUSPEND_SIGNALLED = (1<<1), ///< VM supended execution, either because the script called the built-in wait() script function or because the script consumed too much execution time and was forced by the VM to be suspended for some time
       STMT_ERROR_OCCURRED = (1<<2), ///< VM stopped execution due to some script runtime error that occurred 
    };

    /** @brief Virtual machine execution status.
     *
     * A set of bit flags which reflect the current overall execution status of
     * the virtual machine concerning a certain script execution instance.
     *
     * Since these are bit flags, these constants are bitwise combined.
     */
    enum VMExecStatus_t {
        VM_EXEC_NOT_RUNNING = 0, ///< Script is currently not executed by the VM.
        VM_EXEC_RUNNING = 1, ///< The VM is currently executing the script.
        VM_EXEC_SUSPENDED = (1<<1), ///< Script is currently suspended by the VM, either because the script called the built-in wait() script function or because the script consumed too much execution time and was forced by the VM to be suspended for some time.
        VM_EXEC_ERROR = (1<<2), ///< A runtime error occurred while executing the script (i.e. a call to some built-in script function failed).
    };

    /** @brief Script event handler type.
     *
     * Identifies one of the possible event handler callback types defined by
     * the NKSP script language.
     */
    enum VMEventHandlerType_t {
        VM_EVENT_HANDLER_INIT, ///< Initilization event handler, that is script's "on init ... end on" code block.
        VM_EVENT_HANDLER_NOTE, ///< Note event handler, that is script's "on note ... end on" code block.
        VM_EVENT_HANDLER_RELEASE, ///< Release event handler, that is script's "on release ... end on" code block.
        VM_EVENT_HANDLER_CONTROLLER, ///< Controller event handler, that is script's "on controller ... end on" code block.
    };

    // just symbol prototyping
    class VMIntExpr;
    class VMStringExpr;
    class VMIntArrayExpr;
    class VMStringArrayExpr;

    /** @brief Virtual machine expression
     *
     * This is the abstract base class for all expressions of scripts.
     * Deriving classes must implement the abstract method exprType().
     *
     * An expression within a script is translated into one instance of this
     * class. It allows a high level access for the virtual machine to evaluate
     * and handle expressions appropriately during execution. Expressions are
     * for example all kinds of formulas, function calls, statements or a
     * combination of them. Most of them evaluate to some kind of value, which
     * might be further processed as part of encompassing expressions to outer
     * expression results and so forth.
     */
    class VMExpr {
    public:
        /**
         * Identifies the data type to which the result of this expression
         * evaluates to. This abstract method must be implemented by deriving
         * classes.
         */
        virtual ExprType_t exprType() const = 0;

        /**
         * In case this expression is an integer expression, then this method
         * returns a casted pointer to that VMIntExpr object. It returns NULL
         * if this expression is not an integer expression.
         *
         * @b Note: type casting performed by this method is strict! That means
         * if this expression is i.e. actually a string expression like "12",
         * calling asInt() will @b not cast that numerical string expression to
         * an integer expression 12 for you, instead this method will simply
         * return NULL!
         *
         * @see exprType()
         */
        VMIntExpr* asInt() const;

        /**
         * In case this expression is a string expression, then this method
         * returns a casted pointer to that VMStringExpr object. It returns NULL
         * if this expression is not a string expression.
         *
         * @b Note: type casting performed by this method is strict! That means
         * if this expression is i.e. actually an integer expression like 120,
         * calling asString() will @b not cast that integer expression to a
         * string expression "120" for you, instead this method will simply
         * return NULL!
         *
         * @see exprType()
         */
        VMStringExpr* asString() const;

        /**
         * In case this expression is an integer array expression, then this
         * method returns a casted pointer to that VMIntArrayExpr object. It
         * returns NULL if this expression is not an integer array expression.
         *
         * @b Note: type casting performed by this method is strict! That means
         * if this expression is i.e. an integer expression or a string
         * expression, calling asIntArray() will @b not cast those scalar
         * expressions to an array expression for you, instead this method will
         * simply return NULL!
         *
         * @see exprType()
         */
        VMIntArrayExpr* asIntArray() const;

        /**
         * Returns true in case this expression can be considered to be a
         * constant expression. A constant expression will retain the same
         * value throughout the entire life time of a script and the
         * expression's constant value may be evaluated already at script
         * parse time, which may result in performance benefits during script
         * runtime.
         */
        virtual bool isConstExpr() const = 0;

        bool isModifyable() const;
    };

    /** @brief Virtual machine integer expression
     *
     * This is the abstract base class for all expressions inside scripts which
     * evaluate to an integer (scalar) value. Deriving classes implement the
     * abstract method evalInt() to return the actual integer result value of
     * the expression.
     */
    class VMIntExpr : virtual public VMExpr {
    public:
        /**
         * Returns the result of this expression as integer (scalar) value.
         * This abstract method must be implemented by deriving classes.
         */
        virtual int evalInt() = 0;

        /**
         * Returns always INT_EXPR for instances of this class.
         */
        ExprType_t exprType() const OVERRIDE { return INT_EXPR; }
    };

    /** @brief Virtual machine string expression
     *
     * This is the abstract base class for all expressions inside scripts which
     * evaluate to a string value. Deriving classes implement the abstract
     * method evalStr() to return the actual string result value of the
     * expression.
     */
    class VMStringExpr : virtual public VMExpr {
    public:
        /**
         * Returns the result of this expression as string value. This abstract
         * method must be implemented by deriving classes.
         */
        virtual String evalStr() = 0;

        /**
         * Returns always STRING_EXPR for instances of this class.
         */
        ExprType_t exprType() const OVERRIDE { return STRING_EXPR; }
    };

    /** @brief Virtual Machine Array Value Expression
     *
     * This is the abstract base class for all expressions inside scripts which
     * evaluate to some kind of array value. Deriving classes implement the
     * abstract method arraySize() to return the amount of elements within the
     * array.
     */
    class VMArrayExpr : virtual public VMExpr {
    public:
        /**
         * Returns amount of elements in this array. This abstract method must
         * be implemented by deriving classes.
         */
        virtual int arraySize() const = 0;
    };

    /** @brief Virtual Machine Integer Array Expression
     *
     * This is the abstract base class for all expressions inside scripts which
     * evaluate to an array of integer values. Deriving classes implement the
     * abstract methods arraySize(), evalIntElement() and assignIntElement() to
     * access the individual integer array values.
     */
    class VMIntArrayExpr : virtual public VMArrayExpr {
    public:
        /**
         * Returns the (scalar) integer value of the array element given by
         * element index @a i.
         *
         * @param i - array element index (must be between 0 .. arraySize() - 1)
         */
        virtual int evalIntElement(uint i) = 0;

        /**
         * Changes the current value of an element (given by array element
         * index @a i) of this integer array.
         *
         * @param i - array element index (must be between 0 .. arraySize() - 1)
         * @param value - new integer scalar value to be assigned to that array element
         */
        virtual void assignIntElement(uint i, int value) = 0;

        /**
         * Returns always INT_ARR_EXPR for instances of this class.
         */
        ExprType_t exprType() const OVERRIDE { return INT_ARR_EXPR; }
    };

    /** @brief Arguments (parameters) for being passed to a built-in script function.
     *
     * An argument or a set of arguments passed to a script function are
     * translated by the parser to an instance of this class. This abstract
     * interface class is used by implementations of built-in functions to
     * obtain the individual function argument values being passed to them at
     * runtime.
     */
    class VMFnArgs {
    public:
        /**
         * Returns the amount of arguments going to be passed to the script
         * function.
         */
        virtual int argsCount() const = 0;

        /**
         * Returns the respective argument (requested by argument index @a i) of
         * this set of arguments. This method is called by implementations of
         * built-in script functions to obtain the value of each function
         * argument passed to the function at runtime.
         *
         * @param i - function argument index (indexed from left to right)
         */
        virtual VMExpr* arg(int i) = 0;
    };

    /** @brief Result value returned from a call to a built-in script function.
     *
     * Implementations of built-in script functions return an instance of this
     * object to let the virtual machine obtain the result value of the function
     * call, which might then be further processed by the virtual machine
     * according to the script. It also provides informations about the success
     * or failure of the function call.
     */
    class VMFnResult {
    public:
        /**
         * Returns the result value of the function call, represented by a high
         * level expression object.
         */
        virtual VMExpr* resultValue() = 0;

        /**
         * Provides detailed informations of the success / failure of the
         * function call. The virtual machine is evaluating the flags returned
         * here to decide whether it must abort or suspend execution of the
         * script at this point.
         */
        virtual StmtFlags_t resultFlags() { return STMT_SUCCESS; }
    };

    /** @brief Virtual machine built-in function.
     *
     * Abstract base class for built-in script functions, defining the interface
     * for all built-in script function implementations. All built-in script
     * functions are deriving from this abstract interface class in order to
     * provide their functionality to the virtual machine with this unified
     * interface.
     *
     * The methods of this interface class provide two purposes:
     *
     * 1. When a script is loaded, the script parser uses the methods of this
     *    interface to check whether the script author was calling the
     *    respective built-in script function in a correct way. For example
     *    the parser checks whether the required amount of parameters were
     *    passed to the function and whether the data types passed match the
     *    data types expected by the function. If not, loading the script will
     *    be aborted with a parser error, describing to the user (i.e. script
     *    author) the precise misusage of the respective function.
     * 2. After the script was loaded successfully and the script is executed,
     *    the virtual machine calls the exec() method of the respective built-in
     *    function to provide the actual functionality of the built-in function
     *    call.
     */
    class VMFunction {
    public:
        /**
         * Script data type of the function's return value. If the function does
         * not return any value (void), then it returns EMPTY_EXPR here.
         */
        virtual ExprType_t returnType() = 0;

        /**
         * Minimum amount of function arguments this function accepts. If a
         * script is calling this function with less arguments, the script
         * parser will throw a parser error.
         */
        virtual int minRequiredArgs() const = 0;

        /**
         * Maximum amount of function arguments this functions accepts. If a
         * script is calling this function with more arguments, the script
         * parser will throw a parser error.
         */
        virtual int maxAllowedArgs() const = 0;

        /**
         * Script data type of the function's @c iArg 'th function argument.
         * The information provided here is less strong than acceptsArgType().
         * The parser will compare argument data types provided in scripts by
         * calling acceptsArgType(). The return value of argType() is used by the
         * parser instead to show an appropriate parser error which data type
         * this function usually expects as "default" data type. Reason: a
         * function may accept multiple data types for a certain function
         * argument and would automatically cast the passed argument value in
         * that case to the type it actually needs.
         *
         * @param iArg - index of the function argument in question
         *               (must be between 0 .. maxAllowedArgs() - 1)
         */
        virtual ExprType_t argType(int iArg) const = 0;

        /**
         * This method is called by the parser to check whether arguments
         * passed in scripts to this function are accepted by this function. If
         * a script calls this function with an argument's data type not
         * accepted by this function, the parser will throw a parser error. On
         * such errors the data type returned by argType() will be used to
         * assemble an appropriate error message regarding the precise misusage
         * of the built-in function.
         *
         * @param iArg - index of the function argument in question
         *               (must be between 0 .. maxAllowedArgs() - 1)
         * @param type - script data type used for this function argument by
         *               currently parsed script
         * @return true if the given data type would be accepted for the
         *         respective function argument by the function
         */
        virtual bool acceptsArgType(int iArg, ExprType_t type) const = 0;

        /**
         * This method is called by the parser to check whether some arguments
         * (and if yes which ones) passed to this script function will be
         * modified by this script function. Most script functions simply use
         * their arguments as inputs, that is they only read the argument's
         * values. However some script function may also use passed
         * argument(s) as output variables. In this case the function
         * implementation must return @c true for the respective argument
         * index here.
         *
         * @param iArg - index of the function argument in question
         *               (must be between 0 .. maxAllowedArgs() - 1)
         */
        virtual bool modifiesArg(int iArg) const = 0;

        /**
         * Implements the actual function execution. This exec() method is
         * called by the VM whenever this function implementation shall be
         * executed at script runtime. This method blocks until the function
         * call completed.
         *
         * @param args - function arguments for executing this built-in function
         * @returns function's return value (if any) and general status
         *          informations (i.e. whether the function call caused a
         *          runtime error)
         */
        virtual VMFnResult* exec(VMFnArgs* args) = 0;

        /**
         * Convenience method for function implementations to show warning
         * messages during actual execution of the built-in function.
         *
         * @param txt - runtime warning text to be shown to user
         */
        void wrnMsg(const String& txt);

        /**
         * Convenience method for function implementations to show error
         * messages during actual execution of the built-in function.
         *
         * @param txt - runtime error text to be shown to user
         */
        void errMsg(const String& txt);
    };

    /** @brief Virtual machine relative pointer.
     *
     * POD base of VMIntRelPtr and VMInt8RelPtr structures. Not intended to be
     * used directly. Use VMIntRelPtr or VMInt8RelPtr instead.
     *
     * @see VMIntRelPtr, VMInt8RelPtr
     */
    struct VMRelPtr {
        void** base; ///< Base pointer.
        int offset;  ///< Offset (in bytes) relative to base pointer.
        bool readonly; ///< Whether the pointed data may be modified or just be read.
    };

    /** @brief Pointer to built-in VM integer variable (of C/C++ type int).
     *
     * Used for defining built-in 32 bit integer script variables.
     *
     * @b CAUTION: You may only use this class for pointing to C/C++ variables
     * of type "int" (which on most systems is 32 bit in size). If the C/C++ int
     * variable you want to reference is only 8 bit in size, then you @b must
     * use VMInt8RelPtr instead!
     *
     * For efficiency reasons the actual native C/C++ int variable is referenced
     * by two components here. The actual native int C/C++ variable in memory
     * is dereferenced at VM run-time by taking the @c base pointer dereference
     * and adding @c offset bytes. This has the advantage that for a large
     * number of built-in int variables, only one (or few) base pointer need
     * to be re-assigned before running a script, instead of updating each
     * built-in variable each time before a script is executed.
     *
     * Refer to DECLARE_VMINT() for example code.
     *
     * @see VMInt8RelPtr, DECLARE_VMINT()
     */
    struct VMIntRelPtr : VMRelPtr {
        VMIntRelPtr() {
            base   = NULL;
            offset = 0;
            readonly = false;
        }
        VMIntRelPtr(const VMRelPtr& data) {
            base   = data.base;
            offset = data.offset;
            readonly = false;
        }
        virtual int evalInt() { return *(int*)&(*(uint8_t**)base)[offset]; }
        virtual void assign(int i) { *(int*)&(*(uint8_t**)base)[offset] = i; }
    };

    /** @brief Pointer to built-in VM integer variable (of C/C++ type int8_t).
     *
     * Used for defining built-in 8 bit integer script variables.
     *
     * @b CAUTION: You may only use this class for pointing to C/C++ variables
     * of type "int8_t" (8 bit integer). If the C/C++ int variable you want to
     * reference is an "int" type (which is 32 bit on most systems), then you
     * @b must use VMIntRelPtr instead!
     *
     * For efficiency reasons the actual native C/C++ int variable is referenced
     * by two components here. The actual native int C/C++ variable in memory
     * is dereferenced at VM run-time by taking the @c base pointer dereference
     * and adding @c offset bytes. This has the advantage that for a large
     * number of built-in int variables, only one (or few) base pointer need
     * to be re-assigned before running a script, instead of updating each
     * built-in variable each time before a script is executed.
     *
     * Refer to DECLARE_VMINT() for example code.
     *
     * @see VMIntRelPtr, DECLARE_VMINT()
     */
    struct VMInt8RelPtr : VMIntRelPtr {
        VMInt8RelPtr() : VMIntRelPtr() {}
        VMInt8RelPtr(const VMRelPtr& data) : VMIntRelPtr(data) {}
        virtual int evalInt() OVERRIDE {
            return *(uint8_t*)&(*(uint8_t**)base)[offset];
        }
        virtual void assign(int i) OVERRIDE {
            *(uint8_t*)&(*(uint8_t**)base)[offset] = i;
        }
    };

    /**
     * Convenience macro for initializing VMIntRelPtr and VMInt8RelPtr
     * structures. Usage example:
     * @code
     * struct Foo {
     *   uint8_t a; // native representation of a built-in integer script variable
     *   int b; // native representation of another built-in integer script variable
     *   int c; // native representation of another built-in integer script variable
     *   uint8_t d; // native representation of another built-in integer script variable
     * };
     *
     * // initializing the built-in script variables to some values
     * Foo foo1 = (Foo) { 1, 2000, 3000, 4 };
     * Foo foo2 = (Foo) { 5, 6000, 7000, 8 };
     *
     * Foo* pFoo;
     *
     * VMInt8RelPtr varA = DECLARE_VMINT(pFoo, class Foo, a);
     * VMIntRelPtr  varB = DECLARE_VMINT(pFoo, class Foo, b);
     * VMIntRelPtr  varC = DECLARE_VMINT(pFoo, class Foo, c);
     * VMInt8RelPtr varD = DECLARE_VMINT(pFoo, class Foo, d);
     *
     * pFoo = &foo1;
     * printf("%d\n", varA->evalInt()); // will print 1
     * printf("%d\n", varB->evalInt()); // will print 2000
     * printf("%d\n", varC->evalInt()); // will print 3000
     * printf("%d\n", varD->evalInt()); // will print 4
     *
     * // same printf() code, just with pFoo pointer being changed ...
     *
     * pFoo = &foo2;
     * printf("%d\n", varA->evalInt()); // will print 5
     * printf("%d\n", varB->evalInt()); // will print 6000
     * printf("%d\n", varC->evalInt()); // will print 7000
     * printf("%d\n", varD->evalInt()); // will print 8
     * @endcode
     * As you can see above, by simply changing one single pointer, you can
     * remap a huge bunch of built-in integer script variables to completely
     * different native values/native variables. Which especially reduces code
     * complexity inside the sampler engines which provide the actual script
     * functionalities.
     */
    #define DECLARE_VMINT(basePtr, T_struct, T_member) ( \
        (VMRelPtr) {                                     \
            (void**) &basePtr,                           \
            offsetof(T_struct, T_member),                \
            false                                        \
        }                                                \
    )                                                    \

    /**
     * Same as DECLARE_VMINT(), but this one defines the VMIntRelPtr and
     * VMInt8RelPtr structures to be of read-only type. That means the script
     * parser will abort any script at parser time if the script is trying to
     * modify such a read-only built-in variable.
     *
     * @b NOTE: this is only intended for built-in read-only variables that
     * may change during runtime! If your built-in variable's data is rather
     * already available at parser time and won't change during runtime, then
     * you should rather register a built-in constant in your VM class instead!
     *
     * @see ScriptVM::builtInConstIntVariables()
     */
    #define DECLARE_VMINT_READONLY(basePtr, T_struct, T_member) ( \
        (VMRelPtr) {                                          \
            (void**) &basePtr,                                \
            offsetof(T_struct, T_member),                     \
            true                                              \
        }                                                     \
    )                                                         \

    /** @brief Built-in VM 8 bit integer array variable.
     *
     * Used for defining built-in integer array script variables (8 bit per
     * array element). Currently there is no support for any other kind of array
     * type. So all integer arrays of scripts use 8 bit data types.
     */
    struct VMInt8Array {
        int8_t* data;
        int size;

        VMInt8Array() : data(NULL), size(0) {}
    };

    /** @brief Virtual machine script variable.
     *
     * Common interface for all variables accessed in scripts.
     */
    class VMVariable : virtual public VMExpr {
    public:
        /**
         * Whether a script may modify the content of this variable by
         * assigning a new value to it.
         *
         * @see isConstExpr(), assign()
         */
        virtual bool isAssignable() const = 0;

        /**
         * In case this variable is assignable, this method will be called to
         * perform the value assignment to this variable with @a expr
         * reflecting the new value to be assigned.
         *
         * @param expr - new value to be assigned to this variable
         */
        virtual void assignExpr(VMExpr* expr) = 0;
    };
    
    /** @brief Dynamically executed variable (abstract base class).
     *
     * Interface for the implementation of a dynamically generated content of
     * a built-in script variable. Most built-in variables are simply pointers
     * to some native location in memory. So when a script reads them, the
     * memory location is simply read to get the value of the variable. A
     * dynamic variable however is not simply a memory location. For each access
     * to a dynamic variable some native code is executed to actually generate
     * and provide the content (value) of this type of variable.
     */
    class VMDynVar : public VMVariable {
    public:
        /**
         * Returns true in case this dynamic variable can be considered to be a
         * constant expression. A constant expression will retain the same value
         * throughout the entire life time of a script and the expression's
         * constant value may be evaluated already at script parse time, which
         * may result in performance benefits during script runtime.
         *
         * However due to the "dynamic" behavior of dynamic variables, almost
         * all dynamic variables are probably not constant expressions. That's
         * why this method returns @c false by default. If you are really sure
         * that your dynamic variable implementation can be considered a
         * constant expression then you may override this method and return
         * @c true instead. Note that when you return @c true here, your
         * dynamic variable will really just be executed once; and exectly
         * already when the script is loaded!
         *
         * As an example you may implement a "constant" built-in dynamic
         * variable that checks for a certain operating system feature and
         * returns the result of that OS feature check as content (value) of
         * this dynamic variable. Since the respective OS feature might become
         * available/unavailable after OS updates, software migration, etc. the
         * OS feature check should at least be performed once each time the
         * application is launched. And since the OS feature check might take a
         * certain amount of execution time, it might make sense to only
         * perform the check if the respective variable name is actually
         * referenced at all in the script to be loaded. Note that the dynamic
         * variable will still be evaluated again though if the script is
         * loaded again. So it is up to you to probably cache the result in the
         * implementation of your dynamic variable.
         *
         * On doubt, please rather consider to use a constant built-in script
         * variable instead of implementing a "constant" dynamic variable, due
         * to the runtime overhead a dynamic variable may cause.
         *
         * @see isAssignable()
         */
        bool isConstExpr() const OVERRIDE { return false; }

        /**
         * In case this dynamic variable is assignable, the new value (content)
         * to be assigned to this dynamic variable.
         *
         * By default this method does nothing. Override and implement this
         * method in your subclass in case your dynamic variable allows to
         * assign a new value by script.
         *
         * @param expr - new value to be assigned to this variable
         */
        void assignExpr(VMExpr* expr) OVERRIDE {}
    };

    /** @brief Dynamically executed variable (of integer data type).
     *
     * This is the base class for all built-in integer script variables whose
     * variable content needs to be provided dynamically by executable native
     * code on each script variable access.
     */
    class VMDynIntVar : virtual public VMDynVar, virtual public VMIntExpr {
    public:
    };

    /** @brief Dynamically executed variable (of string data type).
     *
     * This is the base class for all built-in string script variables whose
     * variable content needs to be provided dynamically by executable native
     * code on each script variable access.
     */
    class VMDynStringVar : virtual public VMDynVar, virtual public VMStringExpr {
    public:
    };

    /** @brief Provider for built-in script functions and variables.
     *
     * Abstract base class defining the high-level interface for all classes
     * which add and implement built-in script functions and built-in script
     * variables.
     */
    class VMFunctionProvider {
    public:
        /**
         * Returns pointer to the built-in function with the given function
         * @a name, or NULL if there is no built-in function with that function
         * name.
         *
         * @param name - function name (i.e. "wait" or "message" or "exit", etc.)
         */
        virtual VMFunction* functionByName(const String& name) = 0;

        /**
         * Returns a variable name indexed map of all built-in script variables
         * which point to native "int" scalar (usually 32 bit) variables.
         */
        virtual std::map<String,VMIntRelPtr*> builtInIntVariables() = 0;

        /**
         * Returns a variable name indexed map of all built-in script integer
         * array variables with array element type "int8_t" (8 bit).
         */
        virtual std::map<String,VMInt8Array*> builtInIntArrayVariables() = 0;

        /**
         * Returns a variable name indexed map of all built-in constant script
         * variables, which never change their value at runtime.
         */
        virtual std::map<String,int> builtInConstIntVariables() = 0;

        /**
         * Returns a variable name indexed map of all built-in dynamic variables,
         * which are not simply data stores, rather each one of them executes
         * natively to provide or alter the respective script variable data.
         */
        virtual std::map<String,VMDynVar*> builtInDynamicVariables() = 0;
    };

    /** @brief Execution state of a virtual machine.
     *
     * An instance of this abstract base class represents exactly one execution
     * state of a virtual machine. This encompasses most notably the VM
     * execution stack, and VM polyphonic variables. It does not contain global
     * variables. Global variables are contained in the VMParserContext object.
     * You might see a VMExecContext object as one virtual thread of the virtual
     * machine.
     *
     * In contrast to a VMParserContext, a VMExecContext is not tied to a
     * ScriptVM instance. Thus you can use a VMExecContext with different
     * ScriptVM instances, however not concurrently at the same time.
     *
     * @see VMParserContext
     */
    class VMExecContext {
    public:
        virtual ~VMExecContext() {}

        /**
         * In case the script was suspended for some reason, this method returns
         * the amount of microseconds before the script shall continue its
         * execution. Note that the virtual machine itself does never put its
         * own execution thread(s) to sleep. So the respective class (i.e. sampler
         * engine) which is using the virtual machine classes here, must take
         * care by itself about taking time stamps, determining the script
         * handlers that shall be put aside for the requested amount of
         * microseconds, indicated by this method by comparing the time stamps in
         * real-time, and to continue passing the respective handler to
         * ScriptVM::exec() as soon as its suspension exceeded, etc. Or in other
         * words: all classes in this directory never have an idea what time it
         * is.
         *
         * You should check the return value of ScriptVM::exec() to determine
         * whether the script was actually suspended before calling this method
         * here.
         *
         * @see ScriptVM::exec()
         */
        virtual int suspensionTimeMicroseconds() const = 0;
    };

    /** @brief Script callback for a certain event.
     *
     * Represents a script callback for a certain event, i.e.
     * "on note ... end on" code block.
     */
    class VMEventHandler {
    public:
        /**
         * Type of this event handler, which identifies its purpose. For example
         * for a "on note ... end on" script callback block,
         * @c VM_EVENT_HANDLER_NOTE would be returned here.
         */
        virtual VMEventHandlerType_t eventHandlerType() const = 0;

        /**
         * Name of the event handler which identifies its purpose. For example
         * for a "on note ... end on" script callback block, the name "note"
         * would be returned here.
         */
        virtual String eventHandlerName() const = 0;

        /**
         * Whether or not the event handler makes any use of so called
         * "polyphonic" variables.
         */
        virtual bool isPolyphonic() const = 0;
    };

    /**
     * Encapsulates a noteworty parser issue. This encompasses the type of the
     * issue (either a parser error or parser warning), a human readable
     * explanation text of the error or warning and the location of the
     * encountered parser issue within the script.
     */
    struct ParserIssue {
        String txt; ///< Human readable explanation text of the parser issue.
        int firstLine; ///< The first line number within the script where this issue was encountered (indexed with 1 being the very first line).
        int lastLine; ///< The last line number within the script where this issue was encountered.
        int firstColumn; ///< The first column within the script where this issue was encountered (indexed with 1 being the very first column).
        int lastColumn; ///< The last column within the script where this issue was encountered.
        ParserIssueType_t type; ///< Whether this issue is either a parser error or just a parser warning.

        /**
         * Print this issue out to the console (stdio).
         */
        inline void dump() {
            switch (type) {
                case PARSER_ERROR:
                    printf("[ERROR] line %d, column %d: %s\n", firstLine, firstColumn, txt.c_str());
                    break;
                case PARSER_WARNING:
                    printf("[Warning] line %d, column %d: %s\n", firstLine, firstColumn, txt.c_str());
                    break;
            }
        }

        /**
         * Returns true if this issue is a parser error. In this case the parsed
         * script may not be executed!
         */
        inline bool isErr() const { return type == PARSER_ERROR;   }

        /**
         * Returns true if this issue is just a parser warning. A parsed script
         * that only raises warnings may be executed if desired, however the
         * script may not behave exactly as intended by the script author.
         */
        inline bool isWrn() const { return type == PARSER_WARNING; }
    };

    /**
     * Convenience function used for converting an ExprType_t constant to a
     * string, i.e. for generating error message by the parser.
     */
    inline String typeStr(const ExprType_t& type) {
        switch (type) {
            case EMPTY_EXPR: return "empty";
            case INT_EXPR: return "integer";
            case INT_ARR_EXPR: return "integer array";
            case STRING_EXPR: return "string";
            case STRING_ARR_EXPR: return "string array";
        }
        return "invalid";
    }

    /** @brief Virtual machine representation of a script.
     *
     * An instance of this abstract base class represents a parsed script,
     * translated into a virtual machine tree. You should first check if there
     * were any parser errors. If there were any parser errors, you should
     * refrain from executing the virtual machine. Otherwise if there were no
     * parser errors (i.e. only warnings), then you might access one of the
     * script's event handlers by i.e. calling eventHandlerByName() and pass the
     * respective event handler to the ScriptVM class (or to one of the ScriptVM
     * descendants) for execution.
     *
     * @see VMExecContext, ScriptVM
     */
    class VMParserContext {
    public:
        virtual ~VMParserContext() {}

        /**
         * Returns all noteworthy issues encountered when the script was parsed.
         * These are parser errors and parser warnings.
         */
        virtual std::vector<ParserIssue> issues() const = 0;

        /**
         * Same as issues(), but this method only returns parser errors.
         */
        virtual std::vector<ParserIssue> errors() const = 0;

        /**
         * Same as issues(), but this method only returns parser warnings.
         */
        virtual std::vector<ParserIssue> warnings() const = 0;

        /**
         * Returns the translated virtual machine representation of an event
         * handler block (i.e. "on note ... end on" code block) within the
         * parsed script. This translated representation of the event handler
         * can be executed by the virtual machine.
         *
         * @param index - index of the event handler within the script
         */
        virtual VMEventHandler* eventHandler(uint index) = 0;

        /**
         * Same as eventHandler(), but this method returns the event handler by
         * its name. So for a "on note ... end on" code block of the parsed
         * script you would pass "note" for argument @a name here.
         *
         * @param name - name of the event handler (i.e. "init", "note",
         *               "controller", "release")
         */
        virtual VMEventHandler* eventHandlerByName(const String& name) = 0;
    };

    class SourceToken;

    /** @brief Recognized token of a script's source code.
     *
     * Represents one recognized token of a script's source code, for example
     * a keyword, variable name, etc. and it provides further informations about
     * that particular token, i.e. the precise location (line and column) of the
     * token within the original script's source code.
     *
     * This class is not actually used by the sampler itself. It is rather
     * provided for external script editor applications. Primary purpose of
     * this class is syntax highlighting for external script editors.
     */
    class VMSourceToken {
    public:
        VMSourceToken();
        VMSourceToken(SourceToken* ct);
        VMSourceToken(const VMSourceToken& other);
        virtual ~VMSourceToken();

        // original text of this token as it is in the script's source code
        String text() const;

        // position of token in script
        int firstLine() const; ///< First line this source token is located at in script source code (indexed with 0 being the very first line).
        int firstColumn() const; ///< Last line this source token is located at in script source code.

        // base types
        bool isEOF() const;
        bool isNewLine() const;
        bool isKeyword() const;
        bool isVariableName() const;
        bool isIdentifier() const;
        bool isNumberLiteral() const;
        bool isStringLiteral() const;
        bool isComment() const;
        bool isPreprocessor() const;
        bool isOther() const;

        // extended types
        bool isIntegerVariable() const;
        bool isStringVariable() const;
        bool isArrayVariable() const;
        bool isEventHandlerName() const;

        VMSourceToken& operator=(const VMSourceToken& other);

    private:
        SourceToken* m_token;
    };

} // namespace LinuxSampler

#endif // LS_INSTR_SCRIPT_PARSER_COMMON_H