sly/example/calc/calc.py

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

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

from sly import Lexer, Parser

class CalcLexer(Lexer):
    tokens = (
        'NAME', 'NUMBER',
        )
    ignore = ' \t'
    literals = ['=', '+', '-', '*', '/', '(', ')']

    # Tokens
    NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'

    @_(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, value):
        print("Illegal character '%s'" % value[0])
        self.index += 1

class CalcParser(Parser):
    tokens = CalcLexer.tokens
    
    precedence = (
        ('left', '+', '-'),
        ('left', '*', '/'),
        ('right', 'UMINUS'),
    )

    def __init__(self):
        self.names = { }

    @_('NAME "=" expression')
    def statement(self, p):
        self.names[p[1]] = p[3]

    @_('expression')
    def statement(self, p):
        print(p[1])

    @_('expression "+" expression',
       'expression "-" expression',
       'expression "*" expression',
       'expression "/" expression')
    def expression(self, p):
        if p[2] == '+':
            p[0] = p[1] + p[3]
        elif p[2] == '-':
            p[0] = p[1] - p[3]
        elif p[2] == '*':
            p[0] = p[1] * p[3]
        elif p[2] == '/':
            p[0] = p[1] / p[3]

    @_('"-" expression %prec UMINUS')
    def expression(self, p):
        p[0] = -p[2]

    @_('"(" expression ")"')
    def expression(self, p):
        p[0] = p[2]

    @_('NUMBER')
    def expression(self, p):
        p[0] = p[1]

    @_('NAME')
    def expression(self, p):
        try:
            p[0] = self.names[p[1]]
        except LookupError:
            print("Undefined name '%s'" % p[1])
            p[0] = 0


if __name__ == '__main__':
    lexer = CalcLexer()
    parser = CalcParser()
    while True:
        try:
            text = input('calc > ')
        except EOFError:
            break
        if text:
            parser.parse(lexer.tokenize(text))