Package java_cup

Class lexer

java.lang.Object
java_cup.lexer

public class lexer extends Object
This class implements a small scanner (aka lexical analyzer or lexer) for the JavaCup specification. This scanner reads characters from standard input (System.in) and returns integers corresponding to the terminal number of the next token. Once end of input is reached the EOF token is returned on every subsequent call.

Tokens currently returned include:

    Symbol        Constant Returned     Symbol        Constant Returned
    ------        -----------------     ------        -----------------
    "package"     PACKAGE               "import"      IMPORT 
    "code"        CODE                  "action"      ACTION 
    "parser"      PARSER                "terminal"    TERMINAL
    "non"         NON                   "init"        INIT 
    "scan"        SCAN                  "with"        WITH
    "start"       START                   ;           SEMI 
      ,           COMMA                   *           STAR 
      .           DOT                     :           COLON
      ::=         COLON_COLON_EQUALS      |           BAR
    identifier    ID                    {:...:}       CODE_STRING
  
All symbol constants are defined in sym.java which is generated by JavaCup from parser.cup.

In addition to the scanner proper (called first via init() then with next_token() to get each token) this class provides simple error and warning routines and keeps a count of errors and warnings that is publicly accessible.

This class is "static" (i.e., it has only static members and methods).

  • Field Details

    • next_char

      protected static int next_char
      First character of lookahead.
    • next_char2

      protected static int next_char2
      Second character of lookahead.
    • EOF_CHAR

      protected static final int EOF_CHAR
      EOF constant.
      See Also:
    • keywords

      protected static Hashtable keywords
      Table of keywords. Keywords are initially treated as identifiers. Just before they are returned we look them up in this table to see if they match one of the keywords. The string of the name is the key here, which indexes Integer objects holding the symbol number.
    • char_symbols

      protected static Hashtable char_symbols
      Table of single character symbols. For ease of implementation, we store all unambiguous single character tokens in this table of Integer objects keyed by Integer objects with the numerical value of the appropriate char (currently Character objects have a bug which precludes their use in tables).
    • current_line

      protected static int current_line
      Current line number for use in error messages.
    • current_position

      protected static int current_position
      Character position in current line.
    • error_count

      public static int error_count
      Count of total errors detected so far.
    • warning_count

      public static int warning_count
      Count of warnings issued so far
  • Method Details

    • init

      public static void init() throws IOException
      Initialize the scanner. This sets up the keywords and char_symbols tables and reads the first two characters of lookahead.
      Throws:
      IOException
    • advance

      protected static void advance() throws IOException
      Advance the scanner one character in the input stream. This moves next_char2 to next_char and then reads a new next_char2.
      Throws:
      IOException
    • emit_error

      public static void emit_error(String message)
      Emit an error message. The message will be marked with both the current line number and the position in the line. Error messages are printed on standard error (System.err).
      Parameters:
      message - the message to print.
    • emit_warn

      public static void emit_warn(String message)
      Emit a warning message. The message will be marked with both the current line number and the position in the line. Messages are printed on standard error (System.err).
      Parameters:
      message - the message to print.
    • id_start_char

      protected static boolean id_start_char(int ch)
      Determine if a character is ok to start an id.
      Parameters:
      ch - the character in question.
    • id_char

      protected static boolean id_char(int ch)
      Determine if a character is ok for the middle of an id.
      Parameters:
      ch - the character in question.
    • find_single_char

      protected static int find_single_char(int ch)
      Try to look up a single character symbol, returns -1 for not found.
      Parameters:
      ch - the character in question.
    • swallow_comment

      protected static void swallow_comment() throws IOException
      Handle swallowing up a comment. Both old style C and new style C++ comments are handled.
      Throws:
      IOException
    • do_code_string

      protected static token do_code_string() throws IOException
      Swallow up a code string. Code strings begin with "{:" and include all characters up to the first occurrence of ":}" (there is no way to include ":}" inside a code string). The routine returns an str_token object suitable for return by the scanner.
      Throws:
      IOException
    • do_id

      protected static token do_id() throws IOException
      Process an identifier. Identifiers begin with a letter, underscore, or dollar sign, which is followed by zero or more letters, numbers, underscores or dollar signs. This routine returns an str_token suitable for return by the scanner.
      Throws:
      IOException
    • next_token

      public static token next_token() throws IOException
      Return one token. This is the main external interface to the scanner. It consumes sufficient characters to determine the next input token and returns it. To help with debugging, this routine actually calls real_next_token() which does the work. If you need to debug the parser, this can be changed to call debug_next_token() which prints a debugging message before returning the token.
      Throws:
      IOException
    • debug_next_token

      public static token debug_next_token() throws IOException
      Debugging version of next_token(). This routine calls the real scanning routine, prints a message on System.out indicating what the token is, then returns it.
      Throws:
      IOException
    • real_next_token

      protected static token real_next_token() throws IOException
      The actual routine to return one token. This is normally called from next_token(), but for debugging purposes can be called indirectly from debug_next_token().
      Throws:
      IOException