java_cup
Class lexer
public class lexer
extends java.lang.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 Symbol. Once end of input is reached the EOF Symbol is
returned on every subsequent call.
Symbols 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 "precedence" PRECEDENCE
"left" LEFT "right" RIGHT
"nonassoc" NONASSOC "%prec PRECENT_PREC
[ LBRACK ] RBRACK
; SEMI
, COMMA * STAR
. DOT : COLON
::= COLON_COLON_EQUALS | BAR
identifier ID {:...:} CODE_STRING
"nonterminal" NONTERMINAL
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 Symbol) 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).
Version:
- Frank Flannery
protected static int | EOF_CHAR - EOF constant.
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protected static int | absolute_position - Character position in current line.
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protected static Hashtable | char_symbols - Table of single character symbols.
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protected static int | current_line - Current line number for use in error messages.
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protected static int | current_position - Character position in current line.
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static int | error_count - Count of total errors detected so far.
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protected static Hashtable | keywords - Table of keywords.
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protected static int | next_char - First character of lookahead.
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protected static int | next_char2 - Second character of lookahead.
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protected static int | next_char3 - Second character of lookahead.
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protected static int | next_char4 - Second character of lookahead.
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static int | warning_count - Count of warnings issued so far
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protected static void | advance() - Advance the scanner one character in the input stream.
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static Symbol | debug_next_token() - Debugging version of next_token().
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protected static Symbol | do_code_string() - Swallow up a code string.
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protected static Symbol | do_id() - Process an identifier.
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static void | emit_error(String message) - Emit an error message.
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static void | emit_warn(String message) - Emit a warning message.
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protected static int | find_single_char(int ch) - Try to look up a single character symbol, returns -1 for not found.
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protected static boolean | id_char(int ch) - Determine if a character is ok for the middle of an id.
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protected static boolean | id_start_char(int ch) - Determine if a character is ok to start an id.
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static void | init() - Initialize the scanner.
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static Symbol | next_token() - Return one Symbol.
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protected static Symbol | real_next_token() - The actual routine to return one Symbol.
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protected static void | swallow_comment() - Handle swallowing up a comment.
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EOF_CHAR
protected static final int EOF_CHAR
EOF constant.
- -1
absolute_position
protected static int absolute_position
Character position in current line.
char_symbols
protected static Hashtable char_symbols
Table of single character symbols. For ease of implementation, we
store all unambiguous single character Symbols 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.
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.
next_char
protected static int next_char
First character of lookahead.
next_char2
protected static int next_char2
Second character of lookahead.
next_char3
protected static int next_char3
Second character of lookahead.
next_char4
protected static int next_char4
Second character of lookahead.
warning_count
public static int warning_count
Count of warnings issued so far
advance
protected static void advance()
throws java.io.IOException
Advance the scanner one character in the input stream. This moves
next_char2 to next_char and then reads a new next_char2.
debug_next_token
public static Symbol debug_next_token()
throws java.io.IOException
Debugging version of next_token(). This routine calls the real scanning
routine, prints a message on System.out indicating what the Symbol is,
then returns it.
do_code_string
protected static Symbol do_code_string()
throws java.io.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 a String
object suitable for return by the scanner.
do_id
protected static Symbol do_id()
throws java.io.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 a String suitable
for return by the scanner.
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).
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).
message
- the message to print.
find_single_char
protected static int find_single_char(int ch)
Try to look up a single character symbol, returns -1 for not found.
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.
ch
- the character in question.
id_start_char
protected static boolean id_start_char(int ch)
Determine if a character is ok to start an id.
ch
- the character in question.
init
public static void init()
throws java.io.IOException
Initialize the scanner. This sets up the keywords and char_symbols
tables and reads the first two characters of lookahead.
next_token
public static Symbol next_token()
throws java.io.IOException
Return one Symbol. This is the main external interface to the scanner.
It consumes sufficient characters to determine the next input Symbol
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 Symbol.
real_next_token
protected static Symbol real_next_token()
throws java.io.IOException
The actual routine to return one Symbol. This is normally called from
next_token(), but for debugging purposes can be called indirectly from
debug_next_token().
swallow_comment
protected static void swallow_comment()
throws java.io.IOException
Handle swallowing up a comment. Both old style C and new style C++
comments are handled.