sly/example/calc/calc.py

# -----------------------------------------------------------------------------
# calc.py
# -----------------------------------------------------------------------------

import sys
sys.path.insert(0, "../..")

from sly import Lexer, Parser

class CalcLexer(Lexer):
    # Set of token names.   This is always required
    tokens = { NUMBER, PLUS, MINUS, TIMES, DIVIDE, LPAREN, RPAREN }

    # String containing ignored characters between tokens
    ignore = ' \t'

    # Regular expression rules for tokens
    PLUS    = r'\+'
    MINUS   = r'-'
    TIMES   = r'\*'
    DIVIDE  = r'/'
    LPAREN  = r'\('
    RPAREN  = r'\)'

    @_(r'\d+')
    def NUMBER(self, t):
        t.value = int(t.value)
        return t

    @_(r'\n+')
    def newline(self, t):
        self.lineno += t.value.count('\n')

    def error(self, t):
        print("Illegal character '%s'" % t.value[0])
        self.index += 1

class CalcParser(Parser):
    # Get the token list from the lexer (required)
    tokens = CalcLexer.tokens

    # Grammar rules and actions
    @_('expr PLUS term')
    def expr(self, p):
        return p.expr + p.term

    @_('expr MINUS term')
    def expr(self, p):
        return p.expr - p.term

    @_('term')
    def expr(self, p):
        return p.term

    @_('term TIMES factor')
    def term(self, p):
        return p.term * p.factor

    @_('term DIVIDE factor')
    def term(self, p):
        return p.term / p.factor

    @_('factor')
    def term(self, p):
        return p.factor

    @_('NUMBER')
    def factor(self, p):
        return p.NUMBER

    @_('LPAREN expr RPAREN')
    def factor(self, p):
        return p.expr

if __name__ == '__main__':
    lexer = CalcLexer()
    parser = CalcParser()

    while True:
        try:
            text = input('calc > ')
            result = parser.parse(lexer.tokenize(text))
            print(result)
        except EOFError:
            break