## Creature Project
## CSC323
## 4/17/10
## IterParser.py: Defines a parser that implements an iterator that can
## be used to parse a file containing more than one S-expression


class IterParser():
    def __init__(self, handle):
        '''create a new IterParser by giving it a file handler'''
        with handle as handle:
            self.parse_many(handle.read())

    def parse(self, stuff):
        """Parse a string and return the resulting s-expression.  Only
           works on correctly formatted strings."""
        #print("data is %s" % self.data)
        val = self.parse_kernel(stuff)[0]
        return val

    def parse_many(self, stuff):
        """Parse a string and return a list of the s expressions we've found.
           Only works on properly formatted strings."""
        #print(stuff)
        self.expressions = []
        while (stuff != ""):
            value,stuff = self.parse_kernel(stuff)
            stuff = stuff.lstrip()
            self.expressions.append(value)
        #print(self.expressions)
        return self.expressions

    def parse_kernel(self, stuff):
        """Parse a string and return a pair of what we've parsed and
           the remainder of the string.  Only works correctly on 
           correctly formatted strings."""

        # Skip over whitespace.  Needs improvement
        stuff = stuff.lstrip()

        # Special case: Nothing left
        if (len(stuff) == 0):
            return ("EMPTY","")

        # Handle nested/parenthesized stuff
        elif (stuff[0] == '('):
            contents = []
            # drop the open paren
            stuff = stuff[1:].lstrip()
            while (len(stuff) > 0) and (stuff[0] != ')'):
                (value, rest) = self.parse_kernel(stuff)
                contents.append(value)
                stuff = rest.lstrip()
            # Drop the close paren
            stuff = stuff[1:]
            return (contents,stuff)

        # Unlikely special case
        elif (stuff[0] == ')'):
            return ("RIGHT",stuff)
        # Handle simple symbols/strings
        elif stuff[0].isalnum():
            i = 1
            while i < len(stuff) and stuff[i].isalnum():
                i = i + 1
            return (stuff[0:i], stuff[i:])

        # Something's wrong
        else:
            raise Exception("Syntax Error!")
            
    def __iter__(self):
        '''return self as an iterator'''
        return self
        
    def __next__(self):
       if self.expressions == []:
       
            raise StopIteration
       return self.expressions.pop(0)
 
if __name__=='__main__':
    i = IterParser(open('itertest'))
    for p in i:
        print(p)