# dabeaz/ply

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 # ----------------------------------------------------------------------------- # calc.py # # A simple calculator with variables. This is from O'Reilly's # "Lex and Yacc", p. 63. # ----------------------------------------------------------------------------- import sys sys.path.insert(0,"../..") if sys.version_info[0] >= 3: raw_input = input tokens = ( 'NAME','NUMBER', ) literals = ['=','+','-','*','/', '(',')'] # Tokens t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*' def t_NUMBER(t): r'\d+' t.value = int(t.value) return t t_ignore = " \t" def t_newline(t): r'\n+' t.lexer.lineno += t.value.count("\n") def t_error(t): print("Illegal character '%s'" % t.value[0]) t.lexer.skip(1) # Build the lexer import ply.lex as lex lex.lex() # Parsing rules precedence = ( ('left','+','-'), ('left','*','/'), ('right','UMINUS'), ) # dictionary of names names = { } def p_statement_assign(p): 'statement : NAME "=" expression' names[p[1]] = p[3] def p_statement_expr(p): 'statement : expression' print(p[1]) def p_expression_binop(p): '''expression : expression '+' expression | expression '-' expression | expression '*' expression | expression '/' expression''' 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] def p_expression_uminus(p): "expression : '-' expression %prec UMINUS" p[0] = -p[2] def p_expression_group(p): "expression : '(' expression ')'" p[0] = p[2] def p_expression_number(p): "expression : NUMBER" p[0] = p[1] def p_expression_name(p): "expression : NAME" try: p[0] = names[p[1]] except LookupError: print("Undefined name '%s'" % p[1]) p[0] = 0 def p_error(p,parser): if p: print("Syntax error at '%s'" % p.value) else: print("Syntax error at EOF") import ply.yacc as yacc yacc.yacc() while 1: try: s = raw_input('calc > ') except EOFError: break if not s: continue yacc.parse(s)
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