one-file-projects/term.py

#!/usr/bin/env python

class Token:
    def __init__(self,data=None):
        self.data = data
    def __repr__(self):
        return "%s<%s>" % (self.__class__.__name__, repr(self.data))

class AddOpToken(Token):
    pass

class SubtractOpToken(Token):
    pass

class MultiplyOpToken(Token):
    pass

class DivideOpToken(Token):
    pass

class NumToken(Token):
    pass

class PLeftToken(Token):
    pass

class PRightToken(Token):
    pass

class EOLToken(Token):
    pass

def lex(text):
    END = object()
    it = iter(text)
    c = next(it,END)
    while True:
        if c == END:
            break
        elif c in "0123456789":
            s = ""
            while c != END and c in "0123456789":
                s+=c
                c = next(it,END)
            yield NumToken(int(s))
            continue
        elif c == "+":
            yield AddOpToken()
        elif c == "-":
            yield SubtractOpToken()
        elif c == "*":
            yield MultiplyOpToken()
        elif c == "/":
            yield DivideOpToken()
        elif c == "(":
            yield PLeftToken()
        elif c == ")":
            yield PRightToken()
        elif c == " ":
            pass
        else:
            raise Exception("Unexpected character %s" % c)
        c = next(it,END)

class OperatorNode:
    def __init__(self, left, right):
        self.left = left
        self.right = right

    def calculate(self):
        raise Exception("Not implemented")

    def __repr__(self):
        return "%s < %s, %s >" % (self.__class__.__name__, repr(self.left), repr(self.right))

class AdditionNode(OperatorNode):
    def calculate(self):
        return self.left.calculate() + self.right.calculate()

class SubtractionNode(OperatorNode):
    def calculate(self):
        return self.left.calculate() - self.right.calculate()

class MultiplicationNode(OperatorNode):
    def calculate(self):
        return self.left.calculate() * self.right.calculate()

class DivisionNode(OperatorNode):
    def calculate(self):
        right = self.right.calculate()
        if right == 0:
            raise Exception("Division by Zero Error")
        return self.left.calculate() // right

class NumNode:
    def __init__(self, value):
        self.value = value

    def calculate(self):
        return self.value

    def __repr__(self):
        return "NumNode < %d >" % self.value

# 1. S -> E
# 2. E -> E+T
# 3. E -> E-T
# 4. E -> T
# 5. T -> T*F
# 6. T -> T/F
# 7. T -> F
# 8. F -> ( E )
# 9. F -> num

def reduce_left_right(stack):
    stack.pop() #state
    right = stack.pop()
    stack.pop() #state
    stack.pop() #operator
    stack.pop() #state
    left = stack.pop()

    return left, right


def parse(text):
    it = lex(text)
    T_NUM = NumToken
    T_ADD = AddOpToken
    T_SUB = SubtractOpToken
    T_MUL = MultiplyOpToken
    T_DIV = DivideOpToken
    T_LPAR = PLeftToken
    T_RPAR = PRightToken
    END = EOLToken

    NTS_E = object()
    NTS_T = object()
    NTS_F = object()

    a = object()
    r = object()
    s = object()

    table = [
        { T_NUM: (s,4), T_LPAR: (s,3) },
        { T_ADD: (s,8), T_SUB: (s,9), END: (a,0) },
        { T_ADD: (r,4), T_SUB: (r,4), T_MUL: (s,12), T_DIV: (s,13), T_RPAR: (r,4), END: (r,4) },
        { T_NUM: (s,4), T_LPAR: (s,3) },
        { T_ADD: (r,9), T_SUB: (r,9), T_MUL: (r,9), T_DIV: (r,9), T_RPAR: (r,9), END: (r,9) },
        { T_ADD: (r,7), T_SUB: (r,7), T_MUL: (r,7), T_DIV: (r,7), T_RPAR: (r,7), END: (r,7) },
        { T_ADD: (s,8), T_SUB: (s,9), T_RPAR: (s,7) },
        { T_ADD: (r,8), T_SUB: (r,8), T_MUL: (r,8), T_DIV: (r,8), T_RPAR: (r,8), END: (r,8) },
        { T_NUM: (s,4), T_LPAR: (s,3) },
        { T_NUM: (s,4), T_LPAR: (s,3) },
        { T_ADD: (r,2), T_SUB: (r,2), T_MUL: (s,12), T_DIV: (s,13), T_RPAR: (r,2), END: (r,2) },
        { T_ADD: (r,3), T_SUB: (r,3), T_MUL: (s,12), T_DIV: (s,13), T_RPAR: (r,3), END: (r,3) },
        { T_NUM: (s,4), T_LPAR: (s,3) },
        { T_NUM: (s,4), T_LPAR: (s,3) },
        { T_ADD: (r,5), T_SUB: (r,5), T_MUL: (r,5), T_DIV: (r,5), T_RPAR: (r,5), END: (r,5) },
        { T_ADD: (r,6), T_SUB: (r,6), T_MUL: (r,6), T_DIV: (r,6), T_RPAR: (r,6), END: (r,6) }
    ]

    goto = [
        { NTS_E: 1, NTS_T:2, NTS_F: 5 },
        {},
        {},
        { NTS_E: 6, NTS_T:2, NTS_F: 5 },
        {},
        {},
        {},
        {},
        { NTS_T:10, NTS_F: 5 },
        { NTS_T:11, NTS_F: 5 },
        {},
        {},
        { NTS_F: 14 },
        { NTS_F: 15 },
        {},
        {}
    ]

    stack = []
    stack.append(0)
    lookahead = next(it,END())

    while True:
        try:
            op, dat = table[stack[-1]][lookahead.__class__]
        except KeyError:
            raise Exception("Unexpected token: %s" % repr(lookahead))

        if op == s:
            stack.append( lookahead )
            stack.append( dat )
            lookahead = next(it,END())
        elif op == r:
            # 1. S -> E
            # 2. E -> E+T
            # 3. E -> E-T
            # 4. E -> T
            # 5. T -> T*F
            # 6. T -> T/F
            # 7. T -> F
            # 8. F -> ( E )
            # 9. F -> num
            if dat == 2:
                left, right = reduce_left_right(stack)
                pstate = stack[-1]
                nts = NTS_E
                stack.append( AdditionNode( left, right ) )
            elif dat == 3:
                left, right = reduce_left_right(stack)
                pstate = stack[-1]
                nts = NTS_E
                stack.append( SubtractionNode( left, right ) )
            elif dat == 4:
                stack.pop() #state
                v = stack.pop()
                pstate = stack[-1]
                nts = NTS_E
                stack.append( v )
            elif dat == 5:
                left, right = reduce_left_right(stack)
                pstate = stack[-1]
                nts = NTS_T
                stack.append( MultiplicationNode( left, right ) )
            elif dat == 6:
                left, right = reduce_left_right(stack)
                pstate = stack[-1]
                nts = NTS_T
                stack.append( DivisionNode( left, right ) )
            elif dat == 7:
                stack.pop() #state
                v = stack.pop()
                pstate = stack[-1]
                nts = NTS_T
                stack.append( v )
            elif dat == 8:
                stack.pop() #state
                stack.pop() #rpar
                stack.pop() #state
                v = stack.pop() # inner
                stack.pop() #state
                stack.pop() #lpar
                pstate = stack[-1]
                nts = NTS_F
                stack.append( v )
            elif dat == 9:
                stack.pop() #state
                tok = stack.pop()
                pstate = stack[-1]
                nts = NTS_F
                stack.append( NumNode( tok.data ) )
            else:
                raise Exception("Rule %d not found" % dat)

            try:
                stack.append( goto[pstate][nts] )
            except:
                raise Exception("WTF")
        elif op == a:
            break

    stack.pop()
    return stack.pop()

if __name__ == '__main__':
    l = input("> ")
    print('"%s"' % l)
    print(list(lex(l)))
    ast = parse(l)
    print(repr(ast))
    print(l," = ",ast.calculate())