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diff --git a/ext/ply/README b/ext/ply/README new file mode 100644 index 000000000..35b458d4c --- /dev/null +++ b/ext/ply/README @@ -0,0 +1,249 @@ +PLY (Python Lex-Yacc) Version 1.2 (November 27, 2002) + +David M. Beazley +Department of Computer Science +University of Chicago +Chicago, IL 60637 +beazley@cs.uchicago.edu + +Copyright (C) 2001 David M. Beazley + +$Header: /home/stever/bk/newmem2/ext/ply/README 1.1 03/06/06 14:53:34-00:00 stever@ $ + +This library is free software; you can redistribute it and/or +modify it under the terms of the GNU Lesser General Public +License as published by the Free Software Foundation; either +version 2.1 of the License, or (at your option) any later version. + +This library is distributed in the hope that it will be useful, +but WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU +Lesser General Public License for more details. + +You should have received a copy of the GNU Lesser General Public +License along with this library; if not, write to the Free Software +Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + +See the file COPYING for a complete copy of the LGPL. + +Introduction +============ + +PLY is a 100% Python implementation of the common parsing tools lex +and yacc. Although several other parsing tools are available for +Python, there are several reasons why you might want to consider PLY: + + - The tools are very closely modeled after traditional lex/yacc. + If you know how to use these tools in C, you will find PLY + to be similar. + + - PLY provides *very* extensive error reporting and diagnostic + information to assist in parser construction. The original + implementation was developed for instructional purposes. As + a result, the system tries to identify the most common types + of errors made by novice users. + + - PLY provides full support for empty productions, error recovery, + precedence specifiers, and moderately ambiguous grammars. + + - Parsing is based on LR-parsing which is fast, memory efficient, + better suited to large grammars, and which has a number of nice + properties when dealing with syntax errors and other parsing problems. + Currently, PLY builds its parsing tables using the SLR algorithm which + is slightly weaker than LALR(1) used in traditional yacc. + + - Like John Aycock's excellent SPARK toolkit, PLY uses Python + reflection to build lexers and parsers. This greatly simplifies + the task of parser construction since it reduces the number of files + and eliminates the need to run a separate lex/yacc tool before + running your program. + + - PLY can be used to build parsers for "real" programming languages. + Although it is not ultra-fast due to its Python implementation, + PLY can be used to parse grammars consisting of several hundred + rules (as might be found for a language like C). The lexer and LR + parser are also reasonably efficient when parsing typically + sized programs. + +The original version of PLY was developed for an Introduction to +Compilers course where students used it to build a compiler for a +simple Pascal-like language. Their compiler had to include lexical +analysis, parsing, type checking, type inference, and generation of +assembly code for the SPARC processor. Because of this, the current +implementation has been extensively tested and debugged. In addition, +most of the API and error checking steps have been adapted to address +common usability problems. + +How to Use +========== + +PLY consists of two files : lex.py and yacc.py. To use the system, +simply copy these files to your project and import them like standard +Python modules. + +The file doc/ply.html contains complete documentation on how to use +the system. + +The example directory contains several different examples including a +PLY specification for ANSI C as given in K&R 2nd Ed. Note: To use +the examples, you will need to copy the lex.py and yacc.py files to +the example directory. + +A simple example is found at the end of this document + +Requirements +============ +PLY requires the use of Python 2.0 or greater. It should work on +just about any platform. + +Resources +========= + +More information about PLY can be obtained on the PLY webpage at: + + http://systems.cs.uchicago.edu/ply + +For a detailed overview of parsing theory, consult the excellent +book "Compilers : Principles, Techniques, and Tools" by Aho, Sethi, and +Ullman. The topics found in "Lex & Yacc" by Levine, Mason, and Brown +may also be useful. + +Given that this is the first release, I welcome your comments on how +to improve the current implementation. See the TODO file for things that +still need to be done. + +Acknowledgments +=============== + +A special thanks is in order for all of the students in CS326 who +suffered through about 25 different versions of these tools :-). + +Example +======= + +Here is a simple example showing a PLY implementation of a calculator with variables. + +# ----------------------------------------------------------------------------- +# calc.py +# +# A simple calculator with variables. +# ----------------------------------------------------------------------------- + +tokens = ( + 'NAME','NUMBER', + 'PLUS','MINUS','TIMES','DIVIDE','EQUALS', + 'LPAREN','RPAREN', + ) + +# Tokens + +t_PLUS = r'\+' +t_MINUS = r'-' +t_TIMES = r'\*' +t_DIVIDE = r'/' +t_EQUALS = r'=' +t_LPAREN = r'\(' +t_RPAREN = r'\)' +t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*' + +def t_NUMBER(t): + r'\d+' + try: + t.value = int(t.value) + except ValueError: + print "Integer value too large", t.value + t.value = 0 + return t + +# Ignored characters +t_ignore = " \t" + +def t_newline(t): + r'\n+' + t.lineno += t.value.count("\n") + +def t_error(t): + print "Illegal character '%s'" % t.value[0] + t.skip(1) + +# Build the lexer +import lex +lex.lex() + +# Precedence rules for the arithmetic operators +precedence = ( + ('left','PLUS','MINUS'), + ('left','TIMES','DIVIDE'), + ('right','UMINUS'), + ) + +# dictionary of names (for storing variables) +names = { } + +def p_statement_assign(t): + 'statement : NAME EQUALS expression' + names[t[1]] = t[3] + +def p_statement_expr(t): + 'statement : expression' + print t[1] + +def p_expression_binop(t): + '''expression : expression PLUS expression + | expression MINUS expression + | expression TIMES expression + | expression DIVIDE expression''' + if t[2] == '+' : t[0] = t[1] + t[3] + elif t[2] == '-': t[0] = t[1] - t[3] + elif t[2] == '*': t[0] = t[1] * t[3] + elif t[2] == '/': t[0] = t[1] / t[3] + +def p_expression_uminus(t): + 'expression : MINUS expression %prec UMINUS' + t[0] = -t[2] + +def p_expression_group(t): + 'expression : LPAREN expression RPAREN' + t[0] = t[2] + +def p_expression_number(t): + 'expression : NUMBER' + t[0] = t[1] + +def p_expression_name(t): + 'expression : NAME' + try: + t[0] = names[t[1]] + except LookupError: + print "Undefined name '%s'" % t[1] + t[0] = 0 + +def p_error(t): + print "Syntax error at '%s'" % t.value + +import yacc +yacc.yacc() + +while 1: + try: + s = raw_input('calc > ') + except EOFError: + break + yacc.parse(s) + + + + + + + + + + + + + + + + + |