Package org.antlr.v4.runtime.atn

Class LexerActionExecutor

  • public class LexerActionExecutor
extends Object
    Represents an executor for a sequence of lexer actions which traversed during the matching operation of a lexer rule (token).

    The executor tracks position information for position-dependent lexer actions efficiently, ensuring that actions appearing only at the end of the rule do not cause bloating of the DFA created for the lexer.

    Since:
    4.2
    Author:
    Sam Harwell

    • Constructor Detail

      • LexerActionExecutor

        public LexerActionExecutor​(LexerAction[] lexerActions)
        Constructs an executor for a sequence of LexerAction actions.
        Parameters:
        lexerActions - The lexer actions to execute.

    • Method Detail

      • append

        public static LexerActionExecutor append​(LexerActionExecutor lexerActionExecutor,
                                         LexerAction lexerAction)
        Creates a LexerActionExecutor which executes the actions for the input lexerActionExecutor followed by a specified lexerAction.
        Parameters:
        lexerActionExecutor - The executor for actions already traversed by the lexer while matching a token within a particular LexerATNConfig. If this is null, the method behaves as though it were an empty executor.
        lexerAction - The lexer action to execute after the actions specified in lexerActionExecutor.
        Returns:
        A LexerActionExecutor for executing the combine actions of lexerActionExecutor and lexerAction.

      • fixOffsetBeforeMatch

        public LexerActionExecutor fixOffsetBeforeMatch​(int offset)
        Creates a LexerActionExecutor which encodes the current offset for position-dependent lexer actions.

        Normally, when the executor encounters lexer actions where LexerAction.isPositionDependent() returns true, it calls IntStream.seek(int) on the input CharStream to set the input position to the end of the current token. This behavior provides for efficient DFA representation of lexer actions which appear at the end of a lexer rule, even when the lexer rule matches a variable number of characters.

        Prior to traversing a match transition in the ATN, the current offset from the token start index is assigned to all position-dependent lexer actions which have not already been assigned a fixed offset. By storing the offsets relative to the token start index, the DFA representation of lexer actions which appear in the middle of tokens remains efficient due to sharing among tokens of the same length, regardless of their absolute position in the input stream.

        If the current executor already has offsets assigned to all position-dependent lexer actions, the method returns this.

        Parameters:
        offset - The current offset to assign to all position-dependent lexer actions which do not already have offsets assigned.
        Returns:
        A LexerActionExecutor which stores input stream offsets for all position-dependent lexer actions.

      • getLexerActions

        public LexerAction[] getLexerActions()
        Gets the lexer actions to be executed by this executor.
        Returns:
        The lexer actions to be executed by this executor.

      • execute

        public void execute​(Lexer lexer,
                    CharStream input,
                    int startIndex)
        Execute the actions encapsulated by this executor within the context of a particular Lexer.

        This method calls IntStream.seek(int) to set the position of the input CharStream prior to calling LexerAction.execute(org.antlr.v4.runtime.Lexer) on a position-dependent action. Before the method returns, the input position will be restored to the same position it was in when the method was invoked.

        Parameters:
        lexer - The lexer instance.
        input - The input stream which is the source for the current token. When this method is called, the current IntStream.index() for input should be the start of the following token, i.e. 1 character past the end of the current token.
        startIndex - The token start index. This value may be passed to IntStream.seek(int) to set the input position to the beginning of the token.

      • hashCode

        public int hashCode()
        Overrides:
        hashCode in class Object