import inspect

class Parser:
    def __init__(self, debug=False):
        self.code = ""
        self.debug = debug
        self.position = ""
        self.token = ""
        self.error = ""
    
    def show(self, msg=""):
        if self.debug:
            caller = inspect.stack()[1][3]
            print(self.code+"\n"+" "*self.position+"^")
            print("  "+msg+" from "+caller+"   token="+self.token+"    error="+self.error)
        
        
    def nextToken(self):
        self.token = ""
        # Leerschläge ignorieren
        while self.position<len(self.code) and self.code[self.position]==" ":
            self.position+=1
        # Am Ende angekommen?
        if self.position>=len(self.code):
            self.error = "done"
            return
        # Tokens mit einem Zeichen
        if self.code[self.position] in "()+-*/":
            self.token = self.code[self.position]
            self.position+=1
            return
        # Zahlen
        while self.position<len(self.code) and self.code[self.position] in ".0123456789":
            self.token += self.code[self.position]
            self.position+=1
        
        
                
    def atom(self):
        self.show()
        if self.token=="(":
            self.nextToken()
            a = self.ausdruck()
            if self.token!=")":
                self.error = "Fehlende schliessende Klammer:\n"+self.code+"\n"+" "*self.position+"^"
                self.show(self.error)
                return None
            self.nextToken()
            self.show("a=%d" % a)
            return a
        if self.token=="-":
            self.nextToken()
            a = -self.atom()
            self.show("a=%d" % a)
            return a
        a = float(self.token)
        self.nextToken()
        self.show("a=%d" % a)
        return a
        
        
    def produkt(self):
        self.show()
        a = self.atom()
        while self.error=="" and self.token in "*/":            
            op = self.token
            self.nextToken()
            b = self.atom()
            if op=="*":
                a*=b
            else:
                a/=b
        self.show("a=%d" % a)
        return a
        
    def summe(self):
        self.show()
        a = self.produkt()
        self.show()
        while self.error=="" and self.token in "+-":
            op = self.token
            self.nextToken()
            b = self.produkt()
            if op=="+":
                a+=b
            else:
                a-=b
        self.show("a=%d" % a)
        return a
        
    def ausdruck(self):
        return self.summe()

    def evaluate(self, code):
        self.code = code
        self.position = 0
        self.error = ""
        self.nextToken()
        return self.ausdruck()
        
        
    
p = Parser(False)  # True für detaillierte Ausgabe
for test in ["1+2", "6*7", "-8", "4*2.5+1", "1+-3.5*2", "(1+3)*2", "-(1+3)*-2", "--2", "((2+6/2)+1)*(3+16/4)"]:
    r = p.evaluate(test)
    rr = eval(test)   # Python soll den Ausdruck auswerten
    if (r==rr):
        print(test+" -> %f" % r)
    else:
        print("FAIL on "+test)