131 lines
3 KiB
Python
131 lines
3 KiB
Python
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# -----------------------------------------------------------------------------
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# calc.py
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#
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# A calculator parser that makes use of closures. The function make_calculator()
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# returns a function that accepts an input string and returns a result. All
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# lexing rules, parsing rules, and internal state are held inside the function.
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# -----------------------------------------------------------------------------
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import sys
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sys.path.insert(0,"../..")
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if sys.version_info[0] >= 3:
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raw_input = input
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# Make a calculator function
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def make_calculator():
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import ply.lex as lex
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import ply.yacc as yacc
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# ------- Internal calculator state
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variables = { } # Dictionary of stored variables
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# ------- Calculator tokenizing rules
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tokens = (
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'NAME','NUMBER',
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)
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literals = ['=','+','-','*','/', '(',')']
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t_ignore = " \t"
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t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
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def t_NUMBER(t):
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r'\d+'
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t.value = int(t.value)
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return t
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def t_newline(t):
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r'\n+'
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t.lexer.lineno += t.value.count("\n")
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def t_error(t):
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print("Illegal character '%s'" % t.value[0])
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t.lexer.skip(1)
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# Build the lexer
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lexer = lex.lex()
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# ------- Calculator parsing rules
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precedence = (
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('left','+','-'),
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('left','*','/'),
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('right','UMINUS'),
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)
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def p_statement_assign(p):
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'statement : NAME "=" expression'
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variables[p[1]] = p[3]
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p[0] = None
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def p_statement_expr(p):
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'statement : expression'
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p[0] = p[1]
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def p_expression_binop(p):
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'''expression : expression '+' expression
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| expression '-' expression
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| expression '*' expression
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| expression '/' expression'''
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if p[2] == '+' : p[0] = p[1] + p[3]
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elif p[2] == '-': p[0] = p[1] - p[3]
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elif p[2] == '*': p[0] = p[1] * p[3]
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elif p[2] == '/': p[0] = p[1] / p[3]
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def p_expression_uminus(p):
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"expression : '-' expression %prec UMINUS"
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p[0] = -p[2]
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def p_expression_group(p):
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"expression : '(' expression ')'"
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p[0] = p[2]
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def p_expression_number(p):
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"expression : NUMBER"
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p[0] = p[1]
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def p_expression_name(p):
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"expression : NAME"
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try:
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p[0] = variables[p[1]]
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except LookupError:
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print("Undefined name '%s'" % p[1])
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p[0] = 0
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def p_error(p):
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if p:
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print("Syntax error at '%s'" % p.value)
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else:
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print("Syntax error at EOF")
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# Build the parser
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parser = yacc.yacc()
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# ------- Input function
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def input(text):
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result = parser.parse(text,lexer=lexer)
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return result
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return input
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# Make a calculator object and use it
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calc = make_calculator()
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while True:
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try:
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s = raw_input("calc > ")
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except EOFError:
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break
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r = calc(s)
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if r:
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print(r)
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