Package java_cup

Class production

java.lang.Object
java_cup.production
Direct Known Subclasses:
action_production

public class production extends Object
This class represents a production in the grammar. It contains a LHS non terminal, and an array of RHS symbols. As various transformations are done on the RHS of the production, it may shrink. As a result a separate length is always maintained to indicate how much of the RHS array is still valid.

I addition to construction and manipulation operations, productions provide methods for factoring out actions (see remove_embedded_actions()), for computing the nullability of the production (i.e., can it derive the empty string, see check_nullable()), and operations for computing its first set (i.e., the set of terminals that could appear at the beginning of some string derived from the production, see check_first_set()).

Version:
last updated: 7/3/96
Author:
Frank Flannery
See Also:
  • Field Details

    • _all

      protected static Hashtable _all
      Table of all productions. Elements are stored using their index as the key.
    • next_index

      protected static int next_index
      Static counter for assigning unique index numbers.
    • _lhs

      protected symbol_part _lhs
      The left hand side non-terminal.
    • _rhs_prec

      protected int _rhs_prec
      The precedence of the rule
    • _rhs_assoc

      protected int _rhs_assoc
    • _rhs

      protected production_part[] _rhs
      A collection of parts for the right hand side.
    • _rhs_length

      protected int _rhs_length
      How much of the right hand side array we are presently using.
    • _action

      protected action_part _action
      An action_part containing code for the action to be performed when we reduce with this production.
    • _index

      protected int _index
      Index number of the production.
    • _num_reductions

      protected int _num_reductions
      Count of number of reductions using this production.
    • _nullable_known

      protected boolean _nullable_known
      Is the nullability of the production known or unknown?
    • _nullable

      protected boolean _nullable
      Nullability of the production (can it derive the empty string).
    • _first_set

      protected terminal_set _first_set
      First set of the production. This is the set of terminals that could appear at the front of some string derived from this production.
  • Constructor Details

    • production

      public production(non_terminal lhs_sym, production_part[] rhs_parts, int rhs_l, String action_str) throws internal_error
      Full constructor. This constructor accepts a LHS non terminal, an array of RHS parts (including terminals, non terminals, and actions), and a string for a final reduce action. It does several manipulations in the process of creating a production object. After some validity checking it translates labels that appear in actions into code for accessing objects on the runtime parse stack. It them merges adjacent actions if they appear and moves any trailing action into the final reduce actions string. Next it removes any embedded actions by factoring them out with new action productions. Finally it assigns a unique index to the production.

      Factoring out of actions is accomplished by creating new "hidden" non terminals. For example if the production was originally:

          A ::= B {action} C D
        
      then it is factored into two productions:
          A ::= B X C D
          X ::= {action}
        
      (where X is a unique new non terminal). This has the effect of placing all actions at the end where they can be handled as part of a reduce by the parser.
      Throws:
      internal_error
    • production

      public production(non_terminal lhs_sym, production_part[] rhs_parts, int rhs_l) throws internal_error
      Constructor with no action string.
      Throws:
      internal_error
    • production

      public production(non_terminal lhs_sym, production_part[] rhs_parts, int rhs_l, String action_str, int prec_num, int prec_side) throws internal_error
      Throws:
      internal_error
    • production

      public production(non_terminal lhs_sym, production_part[] rhs_parts, int rhs_l, int prec_num, int prec_side) throws internal_error
      Throws:
      internal_error
  • Method Details

    • all

      public static Enumeration all()
      Access to all productions.
    • find

      public static production find(int indx)
      Lookup a production by index.
    • clear

      public static void clear()
    • number

      public static int number()
      Total number of productions.
    • lhs

      public symbol_part lhs()
      The left hand side non-terminal.
    • precedence_num

      public int precedence_num()
      Access to the precedence of the rule
    • precedence_side

      public int precedence_side()
    • set_precedence_num

      public void set_precedence_num(int prec_num)
      Setting the precedence of a rule
    • set_precedence_side

      public void set_precedence_side(int prec_side)
    • rhs

      public production_part rhs(int indx) throws internal_error
      Access to the collection of parts for the right hand side.
      Throws:
      internal_error
    • rhs_length

      public int rhs_length()
      How much of the right hand side array we are presently using.
    • action

      public action_part action()
      An action_part containing code for the action to be performed when we reduce with this production.
    • index

      public int index()
      Index number of the production.
    • num_reductions

      public int num_reductions()
      Count of number of reductions using this production.
    • note_reduction_use

      public void note_reduction_use()
      Increment the count of reductions with this non-terminal
    • nullable_known

      public boolean nullable_known()
      Is the nullability of the production known or unknown?
    • nullable

      public boolean nullable()
      Nullability of the production (can it derive the empty string).
    • first_set

      public terminal_set first_set()
      First set of the production. This is the set of terminals that could appear at the front of some string derived from this production.
    • is_id_start

      protected static boolean is_id_start(char c)
      Determine if a given character can be a label id starter.
      Parameters:
      c - the character in question.
    • is_id_char

      protected static boolean is_id_char(char c)
      Determine if a character can be in a label id.
      Parameters:
      c - the character in question.
    • make_declaration

      protected String make_declaration(String labelname, String stack_type, int offset)
      Return label declaration code
      Parameters:
      labelname - the label name
      stack_type - the stack type of label?
    • declare_labels

      protected String declare_labels(production_part[] rhs, int rhs_len, String final_action)
      Declare label names as valid variables within the action string
      Parameters:
      rhs - array of RHS parts.
      rhs_len - how much of rhs to consider valid.
      final_action - the final action string of the production.
      lhs_type - the object type associated with the LHS symbol.
    • merge_adjacent_actions

      protected int merge_adjacent_actions(production_part[] rhs_parts, int len)
      Helper routine to merge adjacent actions in a set of RHS parts
      Parameters:
      rhs_parts - array of RHS parts.
      len - amount of that array that is valid.
      Returns:
      remaining valid length.
    • strip_trailing_action

      protected action_part strip_trailing_action(production_part[] rhs_parts, int len)
      Helper routine to strip a trailing action off rhs and return it
      Parameters:
      rhs_parts - array of RHS parts.
      len - how many of those are valid.
      Returns:
      the removed action part.
    • remove_embedded_actions

      protected void remove_embedded_actions() throws internal_error
      Remove all embedded actions from a production by factoring them out into individual action production using new non terminals. if the original production was:
          A ::= B {action1} C {action2} D 
        
      then it will be factored into:
          A ::= B NT$1 C NT$2 D
          NT$1 ::= {action1}
          NT$2 ::= {action2}
        
      where NT$1 and NT$2 are new system created non terminals.
      Throws:
      internal_error
    • check_nullable

      public boolean check_nullable() throws internal_error
      Check to see if the production (now) appears to be nullable. A production is nullable if its RHS could derive the empty string. This results when the RHS is empty or contains only non terminals which themselves are nullable.
      Throws:
      internal_error
    • check_first_set

      public terminal_set check_first_set() throws internal_error
      Update (and return) the first set based on current NT firsts. This assumes that nullability has already been computed for all non terminals and productions.
      Throws:
      internal_error
    • equals

      public boolean equals(production other)
      Equality comparison.
    • equals

      public boolean equals(Object other)
      Generic equality comparison.
      Overrides:
      equals in class Object
    • hashCode

      public int hashCode()
      Produce a hash code.
      Overrides:
      hashCode in class Object
    • toString

      public String toString()
      Convert to a string.
      Overrides:
      toString in class Object
    • to_simple_string

      public String to_simple_string() throws internal_error
      Convert to a simpler string.
      Throws:
      internal_error