Lexical Analyzer:

Symbol Table - Holds the symbols accepted by the lexical analyzer or parser.

Each symbol may be a terminal or a non-terminal.  Terminal symbols are listed first in the table ahead of non-terminals.

Attributes:

• Count - Number of symbols in the table

Child items:

• Symbol

Symbol - Individual symbol accepted by the lexical analyzer or parser. 

Attributes:

• Index - Unique symbol identifier in the symbol table
• Name - Name assigned to symbol in the grammar
• Kind - Indicates the type of symbols.  (0- nonterminal, 1 - terminal, other types are self evident)

Char Sets - Groups of characters that can trigger one (or more) DFA state transitions. 

Attributes:

• Index - Unique identifier for a given character set
• Count - Number of characters in a given character set

Child items:

• Char

Char - Specifies the individual character (no array needed)

Attributes:

• UnicodeIndex - Character code in Unicode (ASCII)

DFA Table - Holds all the DFA states that make up the lexical analyzer. 

Attributes:

• Count - Number of DFA states
• Initial state

Child Items:

• DFA State

DFA State - Enumerates each DFA state and the edges that transition from that state.

Attributes:

• Index - Unique identifier (order in the DFA table)
• EdgeCount - Number of edges from the current state to other DFA states
• AcceptSymbol - Is this an accept state?
  • -1=false
  • Otherwise, it gives the number of the symbol index the state accepts

Child items:

• DFA Edge

DFA Edge - Transition from one DFA state to another

Attributes:

• Char Set Index - Points to the character set whose input causes the transition.  Thus, a single transition may be cause by multiple characters.
• Target - Points to the destination state for the transition

LALR Parser:

Rule Table - Contains definitions of production rules within the grammar.

Attributes:

• Count - Number of production rules in the table

Child items:

• Rule

Rule - Defines a given production rule in the grammar.  Each production rule has a Left Hand Side (LHS) which is a single non-terminal) and a Right Hand Side (RHS), which can be a mix of terminals and non-terminals.  This structure can be used to determine how many and which symbols to pop off the parser stack during a reduction.  The LHS symbol must be placed on the parser stack to complete the rule reduction.

Attributes:

• Index - Unique identifier of rule in the rule table
• NonTerminalIndex - Provides the index for the non-terminal symbol (LHS) in the symbol table.
• Symbol Count - number of symbols in the RHS of the production

Child items:

• Rule Symbol

Rule Symbol - Defines a terminal or non-terminal in the RHS of the rule.  Symbols are listed in order of appearance on the RHS (from leftmost to rightmost). 

Attributes:

• SymbolIndex - Provides the index into the symbol table for the particular symbol on the RHS of the production

LALR Table - This structure represents the LALR parse table.  Recall from class that the LALR table has symbols (terminals and non-terminals) on its X-Axis and LALR states on its Y-Axis (refer to class slides).  This table is defined in terms of states, which call out the appropriate symbols that are applicable to that state. 

Attributes:

• Count - Total number of LALR states in the table
• Initial State - Start state for the parser (nominally state 0)

Child items:

• LALR State

LALR State - This item defines a given state in the LALR parse table.  Each state is mapped to one or more symbols.  For each mapping, an action is specified (shift, reduce, goto, or accept).  If a state does not reference a symbol, then no action is specified when the parser is in that state and the symbol is at the front of the input queue-in short, this is a parser error.

Attributes:

• Index - State number within the table
• Action count - Number of actions associated with a given state (at least one)

Child items:

• LALR Action

LALR Action - This item defines the action for a given state-symbol pair.  Since the LALR Action is a child of LALR State, all listed actions are associated with the parent state.  Each pair will have a single mapping associated with it of type:  shift, reduce, goto, or accept. 

Attributes:

• SymbolIndex - The index of the symbol mapped to the LALR state for this action.
• Action - The type of action being accomplished.  Actions:  1- Shift, 2- Reduce, 3 - Goto, 4 - Accept.
• Value - The meaning of this value is dependent on the action type.  For a shift or goto action, the value refers to the next LALR state.  For a reduce action, the value refers to the rule index in the Rule Table.  For an accept action, the value is meaningless (nominally 0) as it ends the parsing process for a given statement.

Best Programming Strategy:

• Mimic the GPB XML structure
• Implement each structure that has items as an array of objects