primitives.py

#primitives.py - classes used by one or more of the other files.

#a nonterminal is a symbol in a grammar that does expand into additional symbols. 
class NonTerminal:
    symbolType = "NonTerminal"
    def __init__(self, value):
        self.value = value
    def __eq__(self, other):
        if other == None:
            return False
        return self.symbolType == other.symbolType and self.value == other.value
    def __hash__(self):
        return hash((self.value, self.symbolType))
    def __repr__(self):
        return str(self.value)

#a terminal is a symbol used in a grammar that doesn't expand into additional symbols. Typically character literals.
class Terminal:
    symbolType = "Terminal"
    def __init__(self, value):
        self.value = value
    def __eq__(self, other):
        if other == None:
            return False
        return self.symbolType == other.symbolType and self.value == other.value
    def __hash__(self):
        return hash((self.value, self.symbolType))
    def __repr__(self):
        return str(self.value)

#a rule is a NonTerminal left hand side and a right hand side with one or more symbols (can be either terminals or nonterminals or both)
class Rule:
    def __init__(self, LHS, RHS):
        if LHS.symbolType != NonTerminal.symbolType:
            raise Error("Expected terminal symbol")
        self.LHS = LHS
        self.RHS = RHS
    def __eq__(self, other):
        return self.LHS == other.LHS and self.RHS == other.RHS
    def __hash__(self):
        return hash((self.LHS, tuple(self.RHS)))
    def __repr__(self):
        return "{0} -> {1}".format(self.LHS, " ".join(map(str, self.RHS)))

#an Item is a grammar rule with a "special dot" added somewhere on the right hand side.
#See http://en.wikipedia.org/wiki/LR_parser#Constructing_LR.280.29_parsing_tables
#primarily used in SLRtable.py and table.py
class Item:
    def __init__(self, rule, markPos = 0):
        self.rule = rule
        self.markPos = markPos
    def markedSymbol(self):
        if self.markPos >= len(self.rule.RHS):
            return None
        return self.rule.RHS[self.markPos]
    def advanceMarker(self):
        self.markPos += 1
    def copy(self):
        return Item(self.rule, self.markPos)
    def terminating(self):
        return self.markedSymbol() == None
    def matchesRule(self, rule):
        return self.rule == rule
    def __eq__(self, other):
        return self.rule == other.rule and self.markPos == other.markPos
    def __hash__(self):
        return hash((self.rule, self.markPos))
    def __repr__(self):
        ret = str(self.rule.LHS) + " -> "
        RHS = []
        for idx, symbol in enumerate(self.rule.RHS):
            if idx == self.markPos:
                RHS.append(".")
            RHS.append(str(symbol))
        if self.markPos == len(self.rule.RHS):
            RHS.append(".")
        ret = ret + " ".join(RHS)
        return ret

shift = 0
reduce = 1
accept = 2

class Action:
    def __init__(self, action, dest=None):
        self.action = action
        self.destination = dest
    def __repr__(self):
        if self.action == accept:
            return "acc"
        return "s r a".split()[self.action] + str(self.destination)