/*
 *  matiec - a compiler for the programming languages defined in IEC 61131-3
 *  Copyright (C) 2003-2011  Mario de Sousa (msousa@fe.up.pt)
 *  Copyright (C) 2007-2011  Laurent Bessard and Edouard Tisserant
 *
 *  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 3 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, see <http://www.gnu.org/licenses/>.
 *
 *
 * This code is made available on the understanding that it will not be
 * used in safety-critical situations without a full and competent review.
 */

/*
 * An IEC 61131-3 compiler.
 *
 * Based on the
 * FINAL DRAFT - IEC 61131-3, 2nd Ed. (2001-12-10)
 *
 */


/*
 * Definition of the Abstract Syntax data structure components
 */


/*
 * ABSYNTAX.DEF
 *
 * This generates the parse tree structure used to bind the components
 * identified by Bison in the correct syntax order. At the end of the
 * Bison analysis the tree is walked in a sequential fashion generating
 * the relavent code.
 */






/*****************************************************************/
/*****************************************************************/
/*****************************************************************/
/*****************************************************************/
/*                                                               */
/*      safe<xxxxxx> Symbols are defined in:                     */
/*      PLCopen - Technical Committee 5                          */
/*      Safety Software Technical Specification,                 */
/*      Part 1: Concepts and Function Blocks,                    */
/*      Version 1.0 – Official Release - 2006-01-31              */
/*                                                               */
/*****************************************************************/
/*****************************************************************/
/*****************************************************************/
/*****************************************************************/






/*****************************************************************/
/*****************************************************************/
/*****************************************************************/
/*****************************************************************/
/*                                                               */
/*             Symbols defined in:                               */
/*      FINAL DRAFT - IEC 61131-3, 2nd Ed. (2001-12-10)          */
/*                                                               */
/*****************************************************************/
/*****************************************************************/
/*****************************************************************/
/*****************************************************************/

/* Based on the                                    */
/* FINAL DRAFT - IEC 61131-3, 2nd Ed. (2001-12-10) */


/* EN/ENO */
/* NOTE we store 'EN' and 'ENO' tokens in an identifier_c
 *      as they may be used as variables, and it is much easier 
 *      to handle them (fewer special cases) if we do it that way...
 */
/*
SYM_REF0(en_param_c)
SYM_REF0(eno_param_c)
*/

/* A class used to identify an entry (literal, variable, etc...) in the abstract syntax tree with an invalid data type */
/* This is only used from stage3 onwards. Stages 1 and 2 will never create any instances of invalid_type_name_c */
SYM_REF0(invalid_type_name_c)



/********************/
/* 2.1.6 - Pragmas  */
/********************/
SYM_REF0(disable_code_generation_pragma_c)
SYM_REF0(enable_code_generation_pragma_c)
SYM_TOKEN(pragma_c)


/***************************/
/* B 0 - Programming Model */
/***************************/
/* enumvalue_symtable is filled in by enum_declaration_check_c, during stage3 semantic verification, with a list of all enumerated constants declared inside this POU */
SYM_LIST(library_c, enumvalue_symtable_t enumvalue_symtable;)


/*************************/
/* B.1 - Common elements */
/*************************/
/*******************************************/
/* B 1.1 - Letters, digits and identifiers */
/*******************************************/
SYM_TOKEN(identifier_c)
/* A special identifier class, used for identifiers that have been previously declared as a derived datatype */
/*  This is currently needed because generate_c stage 4 needs to handle the array datatype identifiers differently to all other identifiers. */
SYM_TOKEN(derived_datatype_identifier_c) 
SYM_TOKEN(poutype_identifier_c) 


/*********************/
/* B 1.2 - Constants */
/*********************/
/*********************************/
/* B 1.2.XX - Reference Literals */
/*********************************/
/* defined in IEC 61131-3 v3 - Basically the 'NULL' keyword! */
SYM_REF0(ref_value_null_literal_c)

/******************************/
/* B 1.2.1 - Numeric Literals */
/******************************/
SYM_TOKEN(real_c)
SYM_TOKEN(integer_c)
SYM_TOKEN(binary_integer_c)
SYM_TOKEN(octal_integer_c)
SYM_TOKEN(hex_integer_c)

/* Note:
 * We do not have signed_integer_c and signed_real_c classes.
 * These are stored in the parse tree as a integer_c or real_c
 * preceded by a unary minus operator if they are inside an expression,
 * or a neg_integer_c and neg_real_c when used outside an ST expression.
 */
/* Not required:
SYM_TOKEN(signed_integer_c)
SYM_TOKEN(signed_real_c)
*/

/* NOTE: literal __values__ are stored directly in classes such as:
 *          - real_c
 *          - integer_c
 *          - binary_integer_c
 *          - etc...
 *
 *       However, for both the real_c and the integer_c, if they are preceded 
 *       by a '-' negation sign, they are further encapsulated inside 
 *       a neg_literal_c (i.e. the neg_literal_c will point to the 
 *       real_c or integer_c with the value being negated.
 *          neg_literal_c -> integer_literal_c
 *                OR
 *          neg_literal_c -> real_literal_c
 *
 *       However, this has since been changed to...
 *        - replace the neg_literal_c with two distinc classes
 *              (neg_integer_c and neg_real_c), one for each
 *              lietral type. 
 *
 *       This change was done in order to ease the writing of semantic verification (stage3) code.
 *       However, that version of the code has since been replaced by a newer and better algoritm.
 *       This means the above change can now be undone, but there is really no need to undo it,
 *       so we leave it as it is.
 */  
SYM_REF1(neg_real_c, exp)
SYM_REF1(neg_integer_c, exp)

/* Not required:
SYM_REF2(numeric_literal_c, type, value)
*/
SYM_REF2(integer_literal_c, type, value)
SYM_REF2(real_literal_c, type, value)
SYM_REF2(bit_string_literal_c, type, value)
/* A typed or untyped boolean literal... */
/* type may be NULL */
SYM_REF2(boolean_literal_c, type, value)

/* helper class for boolean_literal_c */
SYM_REF0(boolean_true_c)

/* helper class for boolean_literal_c */
SYM_REF0(boolean_false_c)


/*******************************/
/* B.1.2.2   Character Strings */
/*******************************/
SYM_TOKEN(double_byte_character_string_c)
SYM_TOKEN(single_byte_character_string_c)


/***************************/
/* B 1.2.3 - Time Literals */
/***************************/

/************************/
/* B 1.2.3.1 - Duration */
/************************/
SYM_REF0(neg_time_c)
SYM_REF3(duration_c, type_name, neg, interval)
SYM_REF5(interval_c, days, hours, minutes, seconds, milliseconds)
SYM_TOKEN(fixed_point_c)
/*
SYM_REF2(days_c, days, hours)
SYM_REF2(hours_c, hours, minutes)
SYM_REF2(minutes_c, minutes, seconds)
SYM_REF2(seconds_c, seconds, milliseconds)
SYM_REF1(milliseconds_c, milliseconds)
*/

/************************************/
/* B 1.2.3.2 - Time of day and Date */
/************************************/
SYM_REF2(time_of_day_c, type_name, daytime)
SYM_REF3(daytime_c, day_hour, day_minute, day_second)
SYM_REF2(date_c, type_name, date_literal)
SYM_REF3(date_literal_c, year, month, day)
SYM_REF3(date_and_time_c, type_name, date_literal, daytime)


/**********************/
/* B.1.3 - Data types */
/**********************/
/***********************************/
/* B 1.3.1 - Elementary Data Types */
/***********************************/
SYM_REF0(time_type_name_c)
SYM_REF0(bool_type_name_c)
SYM_REF0(sint_type_name_c)
SYM_REF0(int_type_name_c)
SYM_REF0(dint_type_name_c)
SYM_REF0(lint_type_name_c)
SYM_REF0(usint_type_name_c)
SYM_REF0(uint_type_name_c)
SYM_REF0(udint_type_name_c)
SYM_REF0(ulint_type_name_c)
SYM_REF0(real_type_name_c)
SYM_REF0(lreal_type_name_c)
SYM_REF0(date_type_name_c)
SYM_REF0(tod_type_name_c)
SYM_REF0(dt_type_name_c)
SYM_REF0(byte_type_name_c)
SYM_REF0(word_type_name_c)
SYM_REF0(dword_type_name_c)
SYM_REF0(lword_type_name_c)
SYM_REF0(string_type_name_c)
SYM_REF0(wstring_type_name_c)

  /*****************************************************************/
  /* Keywords defined in "Safety Software Technical Specification" */
  /*****************************************************************/

SYM_REF0(safetime_type_name_c)
SYM_REF0(safebool_type_name_c)
SYM_REF0(safesint_type_name_c)
SYM_REF0(safeint_type_name_c)
SYM_REF0(safedint_type_name_c)
SYM_REF0(safelint_type_name_c)
SYM_REF0(safeusint_type_name_c)
SYM_REF0(safeuint_type_name_c)
SYM_REF0(safeudint_type_name_c)
SYM_REF0(safeulint_type_name_c)
SYM_REF0(safereal_type_name_c)
SYM_REF0(safelreal_type_name_c)
SYM_REF0(safedate_type_name_c)
SYM_REF0(safetod_type_name_c)
SYM_REF0(safedt_type_name_c)
SYM_REF0(safebyte_type_name_c)
SYM_REF0(safeword_type_name_c)
SYM_REF0(safedword_type_name_c)
SYM_REF0(safelword_type_name_c)
SYM_REF0(safestring_type_name_c)
SYM_REF0(safewstring_type_name_c)


/********************************/
/* B.1.3.2 - Generic data types */
/********************************/

/* ANY is currently only allowed when defining REF_TO ANY datatypes
 * (equivalent to a (void *)). This is a non standard extension to the
 * standard.
 * Standard library function that use the generic datatypes (ANY_***) are
 * currently handed as overloaded functions, and do not therefore require
 * the use of the generic datatype keywords.
 */
SYM_REF0(generic_type_any_c)            // ANY
/*
SYM_REF0(generic_type_any_derived_c)    // ANY_DERIVED
SYM_REF0(generic_type_any_elementary_c) // ANY_ELEMENTARY
SYM_REF0(generic_type_any_magnitude_c)  // ANY_MAGNITUDE
SYM_REF0(generic_type_any_num_c)        // ANY_NUM
SYM_REF0(generic_type_any_real_c)       // ANY_REAL
SYM_REF0(generic_type_any_int_c)        // ANY_INT
SYM_REF0(generic_type_any_bit_c)        // ANY_BIT
SYM_REF0(generic_type_any_string_c)     // ANY_STRING
SYM_REF0(generic_type_any_date_c)       // ANY_DATE
*/

/********************************/
/* B 1.3.3 - Derived data types */
/********************************/
/*  TYPE type_declaration_list END_TYPE */
SYM_REF1(data_type_declaration_c, type_declaration_list)

/* helper symbol for data_type_declaration */
SYM_LIST(type_declaration_list_c)

/*  simple_type_name ':' simple_spec_init */
SYM_REF2(simple_type_declaration_c, simple_type_name, simple_spec_init)


/* simple_specification ASSIGN constant */
SYM_REF2(simple_spec_init_c, simple_specification, constant)

/*  subrange_type_name ':' subrange_spec_init */
SYM_REF2(subrange_type_declaration_c, subrange_type_name, subrange_spec_init)

/* subrange_specification ASSIGN signed_integer */
SYM_REF2(subrange_spec_init_c, subrange_specification, signed_integer)

/*  integer_type_name '(' subrange')' */
SYM_REF2(subrange_specification_c, integer_type_name, subrange)

/*  signed_integer DOTDOT signed_integer */
/* dimension will be filled in during stage 3 (array_range_check_c) with the number of elements in this subrange */
SYM_REF2(subrange_c, lower_limit, upper_limit, unsigned long long int dimension;)

/*  enumerated_type_name ':' enumerated_spec_init */
SYM_REF2(enumerated_type_declaration_c, enumerated_type_name, enumerated_spec_init)

/* enumerated_specification ASSIGN enumerated_value */
SYM_REF2(enumerated_spec_init_c, enumerated_specification, enumerated_value)

/* helper symbol for enumerated_specification->enumerated_spec_init */
/* enumerated_value_list ',' enumerated_value */
SYM_LIST(enumerated_value_list_c)

/* enumerated_type_name '#' identifier */
SYM_REF2(enumerated_value_c, type, value)

/*  identifier ':' array_spec_init */
SYM_REF2(array_type_declaration_c, identifier, array_spec_init)

/* array_specification [ASSIGN array_initialization] */
/* array_initialization may be NULL ! */
SYM_REF2(array_spec_init_c, array_specification, array_initialization)

/* ARRAY '[' array_subrange_list ']' OF non_generic_type_name */
SYM_REF2(array_specification_c, array_subrange_list, non_generic_type_name)

/* helper symbol for array_specification */
/* array_subrange_list ',' subrange */
SYM_LIST(array_subrange_list_c)

/* array_initialization:  '[' array_initial_elements_list ']' */
/* helper symbol for array_initialization */
/* array_initial_elements_list ',' array_initial_elements */
SYM_LIST(array_initial_elements_list_c)

/* integer '(' [array_initial_element] ')' */
/* array_initial_element may be NULL ! */
SYM_REF2(array_initial_elements_c, integer, array_initial_element)

/*  structure_type_name ':' structure_specification */
SYM_REF2(structure_type_declaration_c, structure_type_name, structure_specification)

/* structure_type_name ASSIGN structure_initialization */
/* structure_initialization may be NULL ! */
SYM_REF2(initialized_structure_c, structure_type_name, structure_initialization)

/* helper symbol for structure_declaration */
/* structure_declaration:  STRUCT structure_element_declaration_list END_STRUCT */
/* structure_element_declaration_list structure_element_declaration ';' */
SYM_LIST(structure_element_declaration_list_c)

/*  structure_element_name ':' *_spec_init */
SYM_REF2(structure_element_declaration_c, structure_element_name, spec_init)

/* helper symbol for structure_initialization */
/* structure_initialization: '(' structure_element_initialization_list ')' */
/* structure_element_initialization_list ',' structure_element_initialization */
SYM_LIST(structure_element_initialization_list_c)

/*  structure_element_name ASSIGN value */
SYM_REF2(structure_element_initialization_c, structure_element_name, value)

/*  string_type_name ':' elementary_string_type_name string_type_declaration_size string_type_declaration_init */
/*
 * NOTE:
 * (Summary: Contrary to what is expected, the
 *           string_type_declaration_c is not used to store
 *           simple string type declarations that do not include
 *           size limits.
 *           For e.g.:
 *             str1_type: STRING := "hello!"
 *           will be stored in a simple_type_declaration_c
 *           instead of a string_type_declaration_c.
 *           The following:
 *             str2_type: STRING [64] := "hello!"
 *           will be stored in a sring_type_declaration_c
 *
 *           Read on for why this is done...
 * End Summary)
 *
 * According to the spec, the valid construct
 * TYPE new_str_type : STRING := "hello!"; END_TYPE
 * has two possible routes to type_declaration...
 *
 * Route 1:
 * type_declaration: single_element_type_declaration
 * single_element_type_declaration: simple_type_declaration
 * simple_type_declaration: identifier ':' simple_spec_init
 * simple_spec_init: simple_specification ASSIGN constant
 * (shift:  identifier <- 'new_str_type')
 * simple_specification: elementary_type_name
 * elementary_type_name: STRING
 * (shift: elementary_type_name <- STRING)
 * (reduce: simple_specification <- elementary_type_name)
 * (shift: constant <- "hello!")
 * (reduce: simple_spec_init: simple_specification ASSIGN constant)
 * (reduce: ...)
 *
 *
 * Route 2:
 * type_declaration: string_type_declaration
 * string_type_declaration: identifier ':' elementary_string_type_name string_type_declaration_size string_type_declaration_init
 * (shift:  identifier <- 'new_str_type')
 * elementary_string_type_name: STRING
 * (shift: elementary_string_type_name <- STRING)
 * (shift: string_type_declaration_size <-  empty )
 * string_type_declaration_init: ASSIGN character_string
 * (shift: character_string <- "hello!")
 * (reduce: string_type_declaration_init <- ASSIGN character_string)
 * (reduce: string_type_declaration <- identifier ':' elementary_string_type_name string_type_declaration_size string_type_declaration_init )
 * (reduce: type_declaration <- string_type_declaration)
 *
 *
 * At first glance it seems that removing route 1 would make
 * the most sense. Unfortunately the construct 'simple_spec_init'
 * shows up multiple times in other rules, so changing this construct
 * would also mean changing all the rules in which it appears.
 * I (Mario) therefore chose to remove route 2 instead. This means
 * that the above declaration gets stored in a
 * simple_type_declaration_c, and not in a string_type_declaration_c
 * as would be expected!
 */
/*  string_type_name ':' elementary_string_type_name string_type_declaration_size string_type_declaration_init */
SYM_REF4(string_type_declaration_c,	string_type_name,
					elementary_string_type_name,
					string_type_declaration_size,
					string_type_declaration_init) /* may be == NULL! */


/* helper symbol for fb_name_decl_c */
/* This symbol/leaf does not exist in the IEC standard syntax as an isolated symbol,
 * as, for some reason, the standard syntax defines FB variable declarations in a slightly 
 * different style as all other spec_init declarations. I.e., fr FBs variable declarations, 
 * the standard defines a single leaf/node (fb_name_decl) that references:
 *   a) the variable name list
 *   b) the FB datatype
 *   c) the FB intial value
 *
 * All other variable declarations break this out into two nodes:
 *   1) references b) and c) above (usually named ***_spec_init)
 *   2) references a), and node 1)
 *
 * In order to allow the datatype analyses to proceed without special cases, we will handle
 * FB variable declarations in the same style. For this reason, we have added the
 * following node to the Abstract Syntax Tree, even though it does not have a direct equivalent in 
 * the standard syntax.
 */
/*  function_block_type_name ASSIGN structure_initialization */
/* structure_initialization -> may be NULL ! */
SYM_REF2(fb_spec_init_c, function_block_type_name, structure_initialization)


/* Taken fron IEC 61131-3 v3
 * // Table 14 - Reference operations
 * Ref_Type_Decl  : Ref_Type_Name ':' Ref_Spec_Init ;
 * Ref_Spec_Init  : Ref_Spec ( ':=' Ref_Value )? ;
 * Ref_Spec       : 'REF_TO' Non_Gen_Type_Name ;
 * Ref_Type_Name  : Identifier ;
 * Ref_Name       : Identifier ;
 * Ref_Value      : Ref_Addr | 'NULL' ;
 * Ref_Addr       : 'REF' '(' (Symbolic_Variable | FB_Name | Class_Instance_Name ) ')' ;
 * Ref_Assign     : Ref_Name ':=' (Ref_Name | Ref_Deref | Ref_Value ) ;
 * Ref_Deref      : 'DREF' '(' Ref_Name ')' ;
 */

/* REF_TO (non_generic_type_name | function_block_type_name) */
SYM_REF1(ref_spec_c, type_name)

/* ref_spec [ ASSIGN ref_initialization ]; */
/* NOTE: ref_initialization may be NULL!!  */
SYM_REF2(ref_spec_init_c, ref_spec, ref_initialization)

/* identifier ':' ref_spec_init */
SYM_REF2(ref_type_decl_c, ref_type_name, ref_spec_init)


/*********************/
/* B 1.4 - Variables */
/*********************/
SYM_REF1(symbolic_variable_c, var_name)

/* symbolic_constant_c is used only when a variable is used inside the subrange of an array declaration
 *    e.g.: ARRAY [1 .. maxval] OF INT
 *  where maxval is a CONSTANT variable. 
 *  When maxval shows up in the POU body,          it will be stored as a standard symbolic_variable_c in the AST.
 *  When maxval shows up in the ARRAY declaration, it will be stored as a          symbolic_constant_c in the AST.
 *  This will allow us to more easily handle this special case, without affecting the remaining working code.
 */ 
SYM_REF1(symbolic_constant_c, var_name)  // a non-standard extension!!

/********************************************/
/* B.1.4.1   Directly Represented Variables */
/********************************************/
SYM_TOKEN(direct_variable_c)

/*************************************/
/* B.1.4.2   Multi-element Variables */
/*************************************/
/*  subscripted_variable '[' subscript_list ']' */
SYM_REF2(array_variable_c, subscripted_variable, subscript_list)

/* subscript_list ',' subscript */
SYM_LIST(subscript_list_c)

/*  record_variable '.' field_selector */
/*  WARNING: input and/or output variables of function blocks
 *           may be accessed as fields of a structured variable!
 *           Code handling a structured_variable_c must take this into account!
 *           (i.e. that a FB instance may be accessed as a structured variable)!
 *
 *  WARNING: Status bit (.X) and activation time (.T) of STEPS in SFC diagrams
 *           may be accessed as fields of a structured variable!
 *           Code handling a structured_variable_c must take this into account 
 *           (i.e. that an SFC STEP may be accessed as a structured variable)!
 */
SYM_REF2(structured_variable_c, record_variable, field_selector)

/******************************************/
/* B 1.4.3 - Declaration & Initialisation */
/******************************************/
SYM_REF0(constant_option_c)
SYM_REF0(retain_option_c)
SYM_REF0(non_retain_option_c)

/* VAR_INPUT [option] input_declaration_list END_VAR */
/* option -> the RETAIN/NON_RETAIN/<NULL> directive... */
/* NOTE: We need to implicitly define the EN and ENO function and FB parameters when the user
 *       does not do it explicitly in the IEC 61131-3 source code. 
 *       To be able to distinguish later on between implictly and explicitly defined
 *       variables, we use the 'method' flag that allows us to remember
 *       whether this declaration was in the original source code (method -> implicit_definition_c) 
 *       or not (method -> explicit_definition_c).
 */
SYM_REF3(input_declarations_c, option, input_declaration_list, method)

/* helper symbol for input_declarations */
SYM_LIST(input_declaration_list_c)

/* NOTE: The formal definition of the standard is erroneous, as it simply does not
 *       consider the EN and ENO keywords!
 *       The semantic description of the languages clearly states that these may be
 *       used in several ways. One of them is to declare an EN input parameter, or
 *       an ENO output parameter.
 *       We have added the 'en_param_declaration_c' and 'eno_param_declaration_c' 
 *       to cover for this.
 *
 *       We could have re-used the standard class used for all other input variables (with
 *       an identifier set to 'EN' or 'ENO') however we may sometimes need to add this
 *       declaration implicitly (if the user does not include it in the source
 *       code himself), and it is good to know whether it was added implicitly or not.
 *       So we create a new class that has a 'method' flag that allows us to remember
 *       whether this declaration was in the original source code (method -> implicit_definition_c) 
 *       or not (method -> explicit_definition_c).
 */
SYM_REF0(implicit_definition_c)
SYM_REF0(explicit_definition_c)
/* type_decl is a simple_spec_init_c */
SYM_REF3(en_param_declaration_c, name, type_decl, method)
SYM_REF3(eno_param_declaration_c, name, type, method)

/* edge -> The F_EDGE or R_EDGE directive */
SYM_REF2(edge_declaration_c, edge, var1_list)

SYM_REF0(raising_edge_option_c)
SYM_REF0(falling_edge_option_c)

/* spec_init is one of the following...
 *    simple_spec_init_c *
 *    subrange_spec_init_c *
 *    enumerated_spec_init_c *
 */
SYM_REF2(var1_init_decl_c, var1_list, spec_init)

/* | var1_list ',' variable_name */
SYM_LIST(var1_list_c)

/* | [var1_list ','] variable_name integer '..' */
/* NOTE: This is an extension to the standard!!! */
/* In order to be able to handle extensible standard functions
 * (i.e. standard functions that may have a variable number of
 * input parameters, such as AND(word#33, word#44, word#55, word#66),
 * we have extended the acceptable syntax to allow var_name '..'
 * in an input variable declaration.
 *
 * This allows us to parse the declaration of standard
 * extensible functions and load their interface definition
 * into the abstract syntax tree just like we do to other 
 * user defined functions.
 * This has the advantage that we can later do semantic
 * checking of calls to functions (be it a standard or user defined
 * function) in (almost) exactly the same way.
 *
 * The integer tells the compiler the number of the first parameter.
 * for example, for ADD(IN1 := 11, IN2:=22), the index for IN starts off at 1.
 * Some other standard library functions, such as MUX, has the extensible
 * variable starting off from 0 (IN0, IN1, IN2, ...).
 *
 * Of course, we have a flag that disables this syntax when parsing user
 * written code, so we only allow this extra syntax while parsing the 
 * 'header' file that declares all the standard IEC 61131-3 functions.
 */
SYM_REF2(extensible_input_parameter_c, var_name, first_index)

/* var1_list ':' array_spec_init */
SYM_REF2(array_var_init_decl_c, var1_list, array_spec_init)

/*  var1_list ':' initialized_structure */
SYM_REF2(structured_var_init_decl_c, var1_list, initialized_structure)

/* fb_name_list ':' function_block_type_name ASSIGN structure_initialization */
/* NOTE: in order to allow datatype handling to proceed using the normal algorithm with no special cases,
 * we will be storing the 
 *    function_block_type_name ASSIGN structure_initialization
 * componentes inside a new node, namely fb_spec_init_c
 */
/* structure_initialization -> may be NULL ! */
SYM_REF2(fb_name_decl_c, fb_name_list, fb_spec_init)

/* fb_name_list ',' fb_name */
SYM_LIST(fb_name_list_c)

/* VAR_OUTPUT [RETAIN | NON_RETAIN] var_init_decl_list END_VAR */
/* option -> may be NULL ! */
/* NOTE: We need to implicitly define the EN and ENO function and FB parameters when the user
 *       does not do it explicitly in the IEC 61131-3 source code. 
 *       To be able to distinguish later on between implictly and explicitly defined
 *       variables, we use the 'method' flag that allows us to remember
 *       whether this declaration was in the original source code (method -> implicit_definition_c) 
 *       or not (method -> explicit_definition_c).
 */
SYM_REF3(output_declarations_c, option, var_init_decl_list, method)

/*  VAR_IN_OUT var_declaration_list END_VAR */
SYM_REF1(input_output_declarations_c, var_declaration_list)

/* helper symbol for input_output_declarations */
/* var_declaration_list var_declaration ';' */
SYM_LIST(var_declaration_list_c)

/*  var1_list ':' array_specification */
SYM_REF2(array_var_declaration_c, var1_list, array_specification)

/*  var1_list ':' structure_type_name */
SYM_REF2(structured_var_declaration_c, var1_list, structure_type_name)

/* VAR [CONSTANT] var_init_decl_list END_VAR */
/* option -> may be NULL ! */
SYM_REF2(var_declarations_c, option, var_init_decl_list)

/*  VAR RETAIN var_init_decl_list END_VAR */
SYM_REF1(retentive_var_declarations_c, var_init_decl_list)

/*  VAR [CONSTANT|RETAIN|NON_RETAIN] located_var_decl_list END_VAR */
/* option -> may be NULL ! */
SYM_REF2(located_var_declarations_c, option, located_var_decl_list)

/* helper symbol for located_var_declarations */
/* located_var_decl_list located_var_decl ';' */
SYM_LIST(located_var_decl_list_c)

/*  [variable_name] location ':' located_var_spec_init */
/* variable_name -> may be NULL ! */
SYM_REF3(located_var_decl_c, variable_name, location, located_var_spec_init)

/*| VAR_EXTERNAL [CONSTANT] external_declaration_list END_VAR */
/* option -> may be NULL ! */
SYM_REF2(external_var_declarations_c, option, external_declaration_list)

/* helper symbol for external_var_declarations */
/*| external_declaration_list external_declaration';' */
SYM_LIST(external_declaration_list_c)

/*  global_var_name ':' (simple_specification|subrange_specification|enumerated_specification|array_specification|prev_declared_structure_type_name|function_block_type_name */
SYM_REF2(external_declaration_c, global_var_name, specification)

/*| VAR_GLOBAL [CONSTANT|RETAIN] global_var_decl_list END_VAR */
/* option -> may be NULL ! */
SYM_REF2(global_var_declarations_c, option, global_var_decl_list)

/* helper symbol for global_var_declarations */
/*| global_var_decl_list global_var_decl ';' */
SYM_LIST(global_var_decl_list_c)

/*| global_var_spec ':' [located_var_spec_init|function_block_type_name] */
/* type_specification ->may be NULL ! */
SYM_REF2(global_var_decl_c, global_var_spec, type_specification)

/*| global_var_name location */
SYM_REF2(global_var_spec_c, global_var_name, location)

/*  AT direct_variable */
SYM_REF1(location_c, direct_variable)

/*| global_var_list ',' global_var_name */
SYM_LIST(global_var_list_c)

/*  var1_list ':' single_byte_string_spec */
SYM_REF2(single_byte_string_var_declaration_c, var1_list, single_byte_string_spec)

/*  STRING ['[' integer ']'] [ASSIGN single_byte_character_string] */
/* integer ->may be NULL ! */
/* single_byte_character_string ->may be NULL ! */
SYM_REF2(single_byte_string_spec_c, string_spec, single_byte_character_string)

/*   STRING ['[' integer ']'] */
/* integer ->may be NULL ! */
SYM_REF2(single_byte_limited_len_string_spec_c, string_type_name, character_string_len)

/*  WSTRING ['[' integer ']'] */
/* integer ->may be NULL ! */
SYM_REF2(double_byte_limited_len_string_spec_c, string_type_name, character_string_len)

/*  var1_list ':' double_byte_string_spec */
SYM_REF2(double_byte_string_var_declaration_c, var1_list, double_byte_string_spec)

/*  WSTRING ['[' integer ']'] [ASSIGN double_byte_character_string] */
/* integer ->may be NULL ! */
/* double_byte_character_string ->may be NULL ! */
SYM_REF2(double_byte_string_spec_c, string_spec, double_byte_character_string)

/*| VAR [RETAIN|NON_RETAIN] incompl_located_var_decl_list END_VAR */
/* option ->may be NULL ! */
SYM_REF2(incompl_located_var_declarations_c, option, incompl_located_var_decl_list)

/* helper symbol for incompl_located_var_declarations */
/*| incompl_located_var_decl_list incompl_located_var_decl ';' */
SYM_LIST(incompl_located_var_decl_list_c)

/*  variable_name incompl_location ':' var_spec */
SYM_REF3(incompl_located_var_decl_c, variable_name, incompl_location, var_spec)

/*  AT incompl_location_token */
SYM_TOKEN(incompl_location_c)

/* intermediate helper symbol for:
 *  - non_retentive_var_decls
 *  - output_declarations
 */
SYM_LIST(var_init_decl_list_c)




/**************************************/
/* B.1.5 - Program organization units */
/**************************************/
/***********************/
/* B 1.5.1 - Functions */
/***********************/
/* enumvalue_symtable is filled in by enum_declaration_check_c, during stage3 semantic verification, with a list of all enumerated constants declared inside this POU */
SYM_REF4(function_declaration_c, derived_function_name, type_name, var_declarations_list, function_body, enumvalue_symtable_t enumvalue_symtable;)

/* intermediate helper symbol for
 * - function_declaration
 * - function_block_declaration
 * - program_declaration
 */
SYM_LIST(var_declarations_list_c)

/* option -> storage method, CONSTANT or <null> */
SYM_REF2(function_var_decls_c, option, decl_list)

/* intermediate helper symbol for function_var_decls */
SYM_LIST(var2_init_decl_list_c)


/*****************************/
/* B 1.5.2 - Function Blocks */
/*****************************/
/*  FUNCTION_BLOCK derived_function_block_name io_OR_other_var_declarations function_block_body END_FUNCTION_BLOCK */
/* enumvalue_symtable is filled in by enum_declaration_check_c, during stage3 semantic verification, with a list of all enumerated constants declared inside this POU */
SYM_REF3(function_block_declaration_c, fblock_name, var_declarations, fblock_body, enumvalue_symtable_t enumvalue_symtable;)

/* intermediate helper symbol for function_declaration */
/*  { io_var_declarations | other_var_declarations }   */
/*
 * NOTE: we re-use the var_declarations_list_c
 */

/*  VAR_TEMP temp_var_decl_list END_VAR */
SYM_REF1(temp_var_decls_c, var_decl_list)

/* intermediate helper symbol for temp_var_decls */
SYM_LIST(temp_var_decls_list_c)

/*  VAR NON_RETAIN var_init_decl_list END_VAR */
SYM_REF1(non_retentive_var_decls_c, var_decl_list)


/**********************/
/* B 1.5.3 - Programs */
/**********************/
/*  PROGRAM program_type_name program_var_declarations_list function_block_body END_PROGRAM */
/* enumvalue_symtable is filled in by enum_declaration_check_c, during stage3 semantic verification, with a list of all enumerated constants declared inside this POU */
SYM_REF3(program_declaration_c, program_type_name, var_declarations, function_block_body, enumvalue_symtable_t enumvalue_symtable;)

/* intermediate helper symbol for program_declaration_c */
/*  { io_var_declarations | other_var_declarations }   */
/*
 * NOTE: we re-use the var_declarations_list_c
 */



/*********************************************/
/* B.1.6  Sequential function chart elements */
/*********************************************/

/* | sequential_function_chart sfc_network */
SYM_LIST(sequential_function_chart_c)

/* initial_step {step | transition | action} */
SYM_LIST(sfc_network_c)

/* INITIAL_STEP step_name ':' action_association_list END_STEP */
SYM_REF2(initial_step_c, step_name, action_association_list)

/* | action_association_list action_association ';' */
SYM_LIST(action_association_list_c)

/* STEP step_name ':' action_association_list END_STEP */
SYM_REF2(step_c, step_name, action_association_list)

/* action_name '(' action_qualifier indicator_name_list ')' */
/* action_qualifier -> may be NULL ! */
SYM_REF3(action_association_c, action_name, action_qualifier, indicator_name_list)

/* N | R | S | P */
SYM_TOKEN(qualifier_c)

/* L | D | SD | DS | SL */
SYM_TOKEN(timed_qualifier_c)

/* | indicator_name_list ',' indicator_name */
SYM_LIST(indicator_name_list_c)

/* qualifier | timed_qualifier ',' action_time */
/* action_time -> may be NULL ! */
SYM_REF2(action_qualifier_c, action_qualifier, action_time)

/* TRANSITION [transition_name] ['(' PRIORITY ASSIGN integer ')'] 
 *   FROM steps TO steps 
 *   transition_condition 
 * END_TRANSITION
*/
/* transition_name -> may be NULL ! */
/* integer -> may be NULL ! */
SYM_REF5(transition_c, transition_name, integer, from_steps, to_steps, transition_condition)

/* ':' eol_list simple_instr_list | ASSIGN expression ';' */
/* transition_condition_il -> may be NULL ! */
/* transition_condition_st -> may be NULL ! */
SYM_REF2(transition_condition_c, transition_condition_il, transition_condition_st)

/* step_name | '(' step_name_list ')' */
/* step_name      -> may be NULL ! */
/* step_name_list -> may be NULL ! */
SYM_REF2(steps_c, step_name, step_name_list)

/* | step_name_list ',' step_name */
SYM_LIST(step_name_list_c)

/* ACTION action_name ':' function_block_body END_ACTION */
SYM_REF2(action_c, action_name, function_block_body)

/********************************/
/* B 1.7 Configuration elements */
/********************************/

/*
CONFIGURATION configuration_name
   optional_global_var_declarations
   (resource_declaration_list | single_resource_declaration)
   optional_access_declarations
   optional_instance_specific_initializations
END_CONFIGURATION
*/
/* enumvalue_symtable is filled in by enum_declaration_check_c, during stage3 semantic verification, with a list of all enumerated constants declared inside this POU */
SYM_REF5(configuration_declaration_c, configuration_name, global_var_declarations, resource_declarations, access_declarations, instance_specific_initializations, enumvalue_symtable_t enumvalue_symtable;)

/* intermediate helper symbol for configuration_declaration  */
/*  { global_var_declarations_list }   */
SYM_LIST(global_var_declarations_list_c)

/* helper symbol for configuration_declaration */
SYM_LIST(resource_declaration_list_c)

/*
RESOURCE resource_name ON resource_type_name
   optional_global_var_declarations
   single_resource_declaration
END_RESOURCE
*/
/* enumvalue_symtable is filled in by enum_declaration_check_c, during stage3 semantic verification, with a list of all enumerated constants declared inside this POU */
SYM_REF4(resource_declaration_c, resource_name, resource_type_name, global_var_declarations, resource_declaration, enumvalue_symtable_t enumvalue_symtable;)

/* task_configuration_list program_configuration_list */
SYM_REF2(single_resource_declaration_c, task_configuration_list, program_configuration_list)

/* helper symbol for single_resource_declaration */
SYM_LIST(task_configuration_list_c)

/* helper symbol for single_resource_declaration */
SYM_LIST(program_configuration_list_c)

/* helper symbol for
 *  - access_path
 *  - instance_specific_init
 */
SYM_LIST(any_fb_name_list_c)

/*  [resource_name '.'] global_var_name ['.' structure_element_name] */
SYM_REF3(global_var_reference_c, resource_name, global_var_name, structure_element_name)

/*  prev_declared_program_name '.' symbolic_variable */
SYM_REF2(program_output_reference_c, program_name, symbolic_variable)

/*  TASK task_name task_initialization */
SYM_REF2(task_configuration_c, task_name, task_initialization)

/*  '(' [SINGLE ASSIGN data_source ','] [INTERVAL ASSIGN data_source ','] PRIORITY ASSIGN integer ')' */
SYM_REF3(task_initialization_c, single_data_source, interval_data_source, priority_data_source)

/*  PROGRAM [RETAIN | NON_RETAIN] program_name [WITH task_name] ':' program_type_name ['(' prog_conf_elements ')'] */
SYM_REF5(program_configuration_c, retain_option, program_name, task_name, program_type_name, prog_conf_elements)

/* prog_conf_elements ',' prog_conf_element */
SYM_LIST(prog_conf_elements_c)

/*  fb_name WITH task_name */
SYM_REF2(fb_task_c, fb_name, task_name)

/*  any_symbolic_variable ASSIGN prog_data_source */
SYM_REF2(prog_cnxn_assign_c, symbolic_variable, prog_data_source)

/* any_symbolic_variable SENDTO data_sink */
SYM_REF2(prog_cnxn_sendto_c, symbolic_variable, data_sink)

/* VAR_CONFIG instance_specific_init_list END_VAR */
SYM_REF1(instance_specific_initializations_c, instance_specific_init_list)

/* helper symbol for instance_specific_initializations */
SYM_LIST(instance_specific_init_list_c)

/* resource_name '.' program_name '.' {fb_name '.'}
    ((variable_name [location] ':' located_var_spec_init) | (fb_name ':' fb_initialization))
*/
SYM_REF6(instance_specific_init_c, resource_name, program_name, any_fb_name_list, variable_name, location, initialization)

/* helper symbol for instance_specific_init */
/* function_block_type_name ':=' structure_initialization */
SYM_REF2(fb_initialization_c, function_block_type_name, structure_initialization)



/****************************************/
/* B.2 - Language IL (Instruction List) */
/****************************************/
/***********************************/
/* B 2.1 Instructions and Operands */
/***********************************/
/*| instruction_list il_instruction */
SYM_LIST(instruction_list_c)

/* | label ':' [il_incomplete_instruction] eol_list */
/* NOTE: The parameters 'prev_il_instruction'/'next_il_instruction' are used to point to all previous/next il instructions that may be executed imedaitely before/after this instruction.
 *       In case of an il instruction preceded by a label, the previous_il_instruction will include all IL instructions that jump to this label!
 *       It is filled in by the flow_control_analysis_c during stage 3.
 *       This will essentially be a doubly linked list of il_instruction_c and il_simple_instruction_c objects!!
 */
SYM_REF2(il_instruction_c, label, il_instruction, std::vector <symbol_c *> prev_il_instruction, next_il_instruction;)


/* | il_simple_operator [il_operand] */
SYM_REF2(il_simple_operation_c, il_simple_operator, il_operand)

/* | function_name [il_operand_list] */
/* NOTE: The parameter 'called_function_declaration', 'extensible_param_count' and 'candidate_functions' are used to pass data between the stage 3 and stage 4.
 *       data between the stage 3 and stage 4.
 *       See the comment above function_invocation_c for more details 
 */
SYM_REF2(il_function_call_c, function_name, il_operand_list, symbol_c *called_function_declaration; int extensible_param_count; std::vector <symbol_c *> candidate_functions;)


/* | il_expr_operator '(' [il_operand] eol_list [simple_instr_list] ')' */
/* WARNING
 *   The semantics of the il_expression_c.il_operand member is NOT what you may expect!
 *   In order to simplify processing of the IL code, stage2 will prepend an artifical (and equivalent) 'LD <il_operand>' IL instruction into the simple_instr_list
 *   The il_expression_c.il_operand is maintained, in case we really need to handle it as a special case!
 *   See the comments in iec_bison.yy for details and an example.
 */
SYM_REF3(il_expression_c, il_expr_operator, il_operand, simple_instr_list)

/*  il_jump_operator label */
SYM_REF2(il_jump_operation_c, il_jump_operator, label)

/*   il_call_operator prev_declared_fb_name
 * | il_call_operator prev_declared_fb_name '(' ')'
 * | il_call_operator prev_declared_fb_name '(' eol_list ')'
 * | il_call_operator prev_declared_fb_name '(' il_operand_list ')'
 * | il_call_operator prev_declared_fb_name '(' eol_list il_param_list ')'
 */
/* NOTE: The parameter 'called_fb_declaration'is used to pass data between stage 3 and stage4 (although currently it is not used in stage 4 */
SYM_REF4(il_fb_call_c, il_call_operator, fb_name, il_operand_list, il_param_list, symbol_c *called_fb_declaration;)


/* | function_name '(' eol_list [il_param_list] ')' */
/* NOTE: The parameter 'called_function_declaration', 'extensible_param_count' and 'candidate_functions' are used to pass data between the stage 3 and stage 4.
 *       See the comment above function_invocation_c for more details. 
 */
SYM_REF2(il_formal_funct_call_c, function_name, il_param_list, symbol_c *called_function_declaration; int extensible_param_count; std::vector <symbol_c *> candidate_functions;)

/* | il_operand_list ',' il_operand */
SYM_LIST(il_operand_list_c)

/* | simple_instr_list il_simple_instruction */
SYM_LIST(simple_instr_list_c)


/* il_simple_instruction:
 *   il_simple_operation eol_list
 * | il_expression eol_list
 * | il_formal_funct_call eol_list
 */
/* NOTE: The parameters 'prev_il_instruction'/'next_il_instruction' are used to point to all previous/next il instructions that may be executed imedaitely before/after this instruction.
 *       In case of an il instruction preceded by a label, the previous_il_instruction will include all IL instructions that jump to this label!
 *       It is filled in by the flow_control_analysis_c during stage 3.
 *       This will essentially be a doubly linked list of il_instruction_c and il_simple_instruction_c objects!!
 */
SYM_REF1(il_simple_instruction_c, il_simple_instruction, std::vector <symbol_c *> prev_il_instruction, next_il_instruction;)

/* | il_initial_param_list il_param_instruction */
SYM_LIST(il_param_list_c)

/*  il_assign_operator il_operand
 * | il_assign_operator '(' eol_list simple_instr_list ')'
 */
SYM_REF3(il_param_assignment_c, il_assign_operator, il_operand, simple_instr_list)

/*  il_assign_out_operator variable */
SYM_REF2(il_param_out_assignment_c, il_assign_out_operator, variable)



/*******************/
/* B 2.2 Operators */
/*******************/
/* NOTE: The parameter 'called_fb_declaration' is used to pass data between stage 3 and stage4 (although currently it is not used in stage 4 */
/* NOTE: The parameter 'deprecated_operation' indicates that the operation, with the specific data types being used, is currently defined
 *       in the standard as being deprecated. This variable is filled in with the correct value in stage 3 (narrow_candidate_datatypes_c) 
 *       and currently only used in stage 3 (print_datatypes_error_c).
 */ 
SYM_REF0(LD_operator_c)
SYM_REF0(LDN_operator_c)
SYM_REF0(ST_operator_c)
SYM_REF0(STN_operator_c)
SYM_REF0(NOT_operator_c)
SYM_REF0(S_operator_c, symbol_c *called_fb_declaration;)
SYM_REF0(R_operator_c, symbol_c *called_fb_declaration;)
SYM_REF0(S1_operator_c, symbol_c *called_fb_declaration;)
SYM_REF0(R1_operator_c, symbol_c *called_fb_declaration;)
SYM_REF0(CLK_operator_c, symbol_c *called_fb_declaration;)
SYM_REF0(CU_operator_c, symbol_c *called_fb_declaration;)
SYM_REF0(CD_operator_c, symbol_c *called_fb_declaration;)
SYM_REF0(PV_operator_c, symbol_c *called_fb_declaration;)
SYM_REF0(IN_operator_c, symbol_c *called_fb_declaration;)
SYM_REF0(PT_operator_c, symbol_c *called_fb_declaration;)
SYM_REF0(AND_operator_c)
SYM_REF0(OR_operator_c)
SYM_REF0(XOR_operator_c)
SYM_REF0(ANDN_operator_c)
SYM_REF0(ORN_operator_c)
SYM_REF0(XORN_operator_c)
SYM_REF0(ADD_operator_c, bool deprecated_operation;)
SYM_REF0(SUB_operator_c, bool deprecated_operation;)
SYM_REF0(MUL_operator_c, bool deprecated_operation;)
SYM_REF0(DIV_operator_c, bool deprecated_operation;)
SYM_REF0(MOD_operator_c)
SYM_REF0(GT_operator_c)
SYM_REF0(GE_operator_c)
SYM_REF0(EQ_operator_c)
SYM_REF0(LT_operator_c)
SYM_REF0(LE_operator_c)
SYM_REF0(NE_operator_c)
SYM_REF0(CAL_operator_c)
SYM_REF0(CALC_operator_c)
SYM_REF0(CALCN_operator_c)
SYM_REF0(RET_operator_c)
SYM_REF0(RETC_operator_c)
SYM_REF0(RETCN_operator_c)
SYM_REF0(JMP_operator_c)
SYM_REF0(JMPC_operator_c)
SYM_REF0(JMPCN_operator_c)

/*  any_identifier ASSIGN */
SYM_REF1(il_assign_operator_c, variable_name)

/*| [NOT] any_identifier SENDTO */
SYM_REF2(il_assign_out_operator_c, option, variable_name)



/***************************************/
/* B.3 - Language ST (Structured Text) */
/***************************************/
/***********************/
/* B 3.1 - Expressions */
/***********************/
SYM_REF1(  ref_expression_c, exp)  /* an extension to the IEC 61131-3 standard - based on the IEC 61131-3 v3 standard.  REF() -> returns address of the varible! */
SYM_REF1(deref_expression_c, exp)  /* an extension to the IEC 61131-3 standard - based on the IEC 61131-3 v3 standard. DREF() -> dereferences an address!        */
SYM_REF1(deref_operator_c,   exp)  /* an extension to the IEC 61131-3 standard - based on the IEC 61131-3 v3 standard.    ^   -> dereferences an address!        */
SYM_REF2( or_expression_c, l_exp, r_exp)
SYM_REF2(xor_expression_c, l_exp, r_exp)
SYM_REF2(and_expression_c, l_exp, r_exp)
SYM_REF2(equ_expression_c, l_exp, r_exp)
SYM_REF2(notequ_expression_c, l_exp, r_exp)
SYM_REF2( lt_expression_c, l_exp, r_exp)
SYM_REF2( gt_expression_c, l_exp, r_exp)
SYM_REF2( le_expression_c, l_exp, r_exp)
SYM_REF2( ge_expression_c, l_exp, r_exp)
SYM_REF2(add_expression_c, l_exp, r_exp, bool deprecated_operation;)
SYM_REF2(sub_expression_c, l_exp, r_exp, bool deprecated_operation;)
SYM_REF2(mul_expression_c, l_exp, r_exp, bool deprecated_operation;)
SYM_REF2(div_expression_c, l_exp, r_exp, bool deprecated_operation;)
SYM_REF2(mod_expression_c, l_exp, r_exp)
SYM_REF2(power_expression_c, l_exp, r_exp)
SYM_REF1(neg_expression_c, exp)
SYM_REF1(not_expression_c, exp)

/*    formal_param_list -> may be NULL ! */
/* nonformal_param_list -> may be NULL ! */
/* NOTES:
 *    The parameter 'called_function_declaration'... 
 *       ...is used to pass data between the stage 3 and stage 4.
 *       The IEC 61131-3 standard allows for overloaded standard functions. This means that some
 *       function calls are not completely defined by the name of the function being called,
 *       and need to be disambiguated with using the data types of the parameters being passed.
 *       Stage 3 does this to verify semantic correctness.
 *       Stage 4 also needs to do this in order to determine which function to call.
 *       It does not make sense to determine the exact function being called twice (once in stage 3,
 *       and again in stage 4), so stage 3 will store this info in the parameter called_function_declaration
 *       for stage 4 to use it later on.
 *    The parameter 'candidate_functions'... 
 *       ...is used to pass data between two passes within stage 3
 *       (actually between fill_candidate_datatypes_c and narrow_candidate_datatypes_c).
 *       It is used to store all the functions that may be legally called with the current parameters
 *       being used in this function invocation. Note that the standard includes some standard functions
 *       that have the exact same input parameter types, but return different data types.
 *       In order to determine which of these functions should be called, we first create a list
 *       of all possible functions, and then narrow down the list (hopefully down to 1 function)
 *       once we know the data type that the function invocation must return (this will take into 
 *       account the expression in which the function invocation is inserted/occurs).
 *       The 'called_function_declaration' will eventually be set (in stage 3) to one of
 *       the functions in the 'candidate_functions' list!
 *    The parameter 'extensible_param_count'... 
 *       ...is used to pass data between the stage 3 and stage 4.
 *       The IEC 61131-3 standard allows for extensible standard functions. This means that some
 *       standard functions may be called with a variable number of paramters. Stage 3 will store
 *       in extensible_param_count the number of parameters being passed to the extensible parameter.
 */
SYM_REF3(function_invocation_c, function_name, formal_param_list, nonformal_param_list, symbol_c *called_function_declaration; int extensible_param_count; std::vector <symbol_c *> candidate_functions;)


/********************/
/* B 3.2 Statements */
/********************/
SYM_LIST(statement_list_c)


/*********************************/
/* B 3.2.1 Assignment Statements */
/*********************************/
SYM_REF2(assignment_statement_c, l_exp, r_exp)


/*****************************************/
/* B 3.2.2 Subprogram Control Statements */
/*****************************************/

/*  RETURN */
SYM_REF0(return_statement_c)

/* fb_name '(' [param_assignment_list] ')' */
/*    formal_param_list -> may be NULL ! */
/* nonformal_param_list -> may be NULL ! */
/* NOTE: The parameter 'called_fb_declaration'is used to pass data between stage 3 and stage4 (although currently it is not used in stage 4 */
SYM_REF3(fb_invocation_c, fb_name, formal_param_list, nonformal_param_list, symbol_c *called_fb_declaration;)

/* helper symbol for fb_invocation */
/* param_assignment_list ',' param_assignment */
SYM_LIST(param_assignment_list_c)

/*  variable_name ASSIGN expression */
SYM_REF2(input_variable_param_assignment_c, variable_name, expression)

/* [NOT] variable_name '=>' variable */
SYM_REF3(output_variable_param_assignment_c, not_param, variable_name, variable)

/* helper CLASS for output_variable_param_assignment */
SYM_REF0(not_paramassign_c)


/********************************/
/* B 3.2.3 Selection Statements */
/********************************/
/* IF expression THEN statement_list elseif_statement_list ELSE statement_list END_IF */
SYM_REF4(if_statement_c, expression, statement_list, elseif_statement_list, else_statement_list)

/* helper symbol for if_statement */
SYM_LIST(elseif_statement_list_c)

/* helper symbol for elseif_statement_list */
/* ELSIF expression THEN statement_list    */
SYM_REF2(elseif_statement_c, expression, statement_list)

/* CASE expression OF case_element_list ELSE statement_list END_CASE */
SYM_REF3(case_statement_c, expression, case_element_list, statement_list)

/* helper symbol for case_statement */
SYM_LIST(case_element_list_c)

/*  case_list ':' statement_list */
SYM_REF2(case_element_c, case_list, statement_list)

SYM_LIST(case_list_c)


/********************************/
/* B 3.2.4 Iteration Statements */
/********************************/
/*  FOR control_variable ASSIGN expression TO expression [BY expression] DO statement_list END_FOR */
SYM_REF5(for_statement_c, control_variable, beg_expression, end_expression, by_expression, statement_list)

/*  WHILE expression DO statement_list END_WHILE */
SYM_REF2(while_statement_c, expression, statement_list)

/*  REPEAT statement_list UNTIL expression END_REPEAT */
SYM_REF2(repeat_statement_c, statement_list, expression)

/*  EXIT */
SYM_REF0(exit_statement_c)


