GlassGhost / GFG-parser

GFG parser generator for context-free grammar.

Compiler-compiler

We implement this parser generator based on "Parsing with Picture" , Keshav Pingali and Gianfranco Bilardi [ ref ]

It's modify of the Earley's algorithm that easier to understand. we use Grammar Flow Graph (GFG) as a representation of Context Free Grammar (CFG) to parse code.

GFG is tool that can reformulated parsing problem to the problem of finding certain kinds of path in graph.

TODO

• debug mode
• not support epsilon production
• EBNF format
• testing
• cannot parser multiple tree
• documentation
• used label in GFG

Installation

• Clone our project

git clone https://[e-mail]/kramatk/earleyparser.git

• Link our lib to your $PYTHONPATH

sudo ln -s noom /usr/lib/python2.7/noom

• Set your $PATH

export PATH=$PATH:/your/absolute/path/

• Make our project execuable

cd noom chmod +x Noom.py

Usage

• create your Grammar

root -> exp
exp -> LPAREN exp PLUS exp RPAREN | LPAREN exp MINUS exp RPAREN
exp -> NUMBER

• create your Lexicon base on PLY tools

# List of token names.   This is always required
tokens = (
   'NUMBER',
   'PLUS',
   'MINUS',
   'TIMES',
   'DIVIDE',
   'LPAREN',
   'RPAREN',
)

# Regular expression rules for simple tokens
t_PLUS    = r'\+'
t_MINUS   = r'-'
t_TIMES   = r'\*'
t_DIVIDE  = r'/'
t_LPAREN  = r'\('
t_RPAREN  = r'\)'

# A regular expression rule with some action code
def t_NUMBER(t):
    r'\d+'
    t.value = int(t.value)    
    return t

# Define a rule so we can track line numbers
def t_newline(t):
    r'\n+'
    t.lexer.lineno += len(t.value)

# A string containing ignored characters (spaces and tabs)
t_ignore  = ' \t'

# Error handling rule
def t_error(t):
    "lexicon error"    
    raise Exception("Illegal character '%s'" % t.value[0])     
    t.lexer.skip(1)

• create your compiler

Noom.py [lexicon] [grammar] -o [compiler/name].py

• modify your compiler

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Learn More

• Documentation