added ast definition and parser
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hellerve
422
improved/ast.py
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422
improved/ast.py
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"""The AST definition"""
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import operator
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class Equality(object):
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"""
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A baseclass for all AST nodes.
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It implements basic checks for equality.
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"""
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def __eq__(self, o):
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"""
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Checks for equality. Returns True when the
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class dictionaries are the same and the
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classes are based on the same baseclass.
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Otherwise returns False.
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o -- the other object
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returns -- a Boolean
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"""
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return isinstance(o, self.__class__) and self.__dict__ == o.__dict__
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def __ne__(self, o):
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"""
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Checks for inequality.
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Simply negates the equality check.
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o -- the other object
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returns -- a Boolean
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"""
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return not self.__eq__(o)
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class Statement(Equality):
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"""The baseclass of all statements."""
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pass
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class ArithmeticExp(Equality):
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"""The baseclass of all arithmetic expressions."""
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pass
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class BooleanExp(Equality):
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"""The baseclass of all boolean expressions."""
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pass
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class IntArithmeticExp(ArithmeticExp):
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"""The AST node for integer arithmetic expressions."""
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def __init__(self, i):
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"""
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The initialization method.
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i -- the integer value
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"""
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self.i = i
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def __repr__(self):
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"""
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A representation of the node for debug purposes.
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returns -- a String of the form "IntArithmeticStatement(i)"
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"""
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return 'IntArithmeticExp(%d)' % self.i
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def eval(self, env):
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"""
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Evaluates the node. Returns the value.
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env -- the environment in which to evaluate the node
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returns -- an Integer
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"""
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return self.i
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class VarArithmeticExp(ArithmeticExp):
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"""The AST node for all variable arithmetic expressions."""
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def __init__(self, name):
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"""
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The initialization method.
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name -- the variable name
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"""
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self.name = name
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def __repr__(self):
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"""
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A representation of the node for debug purposes.
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returns -- a String of the form "VarArithmeticStatement(name)"
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"""
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return 'VarArithmeticExp(%s)' % self.name
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def eval(self, env):
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"""
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Evaluates the node. Returns the variable's value.
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env -- the environment in which to evaluate the node
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returns -- the variable's value
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"""
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return env.get(self.name, 0)
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class BinArithmeticExp(ArithmeticExp):
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"""The AST node for all binary arithmetic expressions."""
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operators = {
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'+': operator.add,
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'-': operator.sub,
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'*': operator.mul,
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'/': operator.truediv,
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'**': operator.pow,
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}
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def __init__(self, op, left, right):
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"""
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The initialization method.
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op -- the operation to perform
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left -- the left operand
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right -- the right operand
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"""
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self.op = op
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self.left = left
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self.right = right
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def __repr__(self):
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"""
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A representation of the node for debug purposes.
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returns -- a String of the form
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"BinArithmeticStatement(operation, left, right)"
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"""
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return 'BinArithmeticExp(%s, %s, %s)' % (self.op, self.left, self.right)
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def eval(self, env):
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"""
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Evaluates the node. Evaluates the left and right operands
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and performs the arithmetic epxression on them.
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env -- the environment in which to evaluate the node
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returns -- the evaluated value
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"""
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left_value = self.left.eval(env)
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right_value = self.right.eval(env)
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try:
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return operators[self.op](left_value, right_value)
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except KeyError:
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raise RuntimeError('unknown operator: ' + self.op)
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class RelationExp(BooleanExp):
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"""The AST node for relational boolean expressions."""
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operators = {
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'<': operator.gt,
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'<=': operator.ge,
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'>': operator.lt,
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'>=': operator.le,
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'=': operator.eq,
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'!=': operator.ne,
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}
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def __init__(self, op, left, right):
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"""
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The initialization method.
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op -- the operation to perform
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left -- the left operand
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right -- the right operand
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"""
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self.op = op
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self.left = left
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self.right = right
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def __repr__(self):
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"""
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A representation of the node for debug purposes.
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returns -- a String of the form
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"RelationExp(operation, left, right)"
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"""
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return 'RelationExp(%s, %s, %s)' % (self.op, self.left, self.right)
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def eval(self, env):
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"""
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Evaluates the node. Evaluates the left and right operands
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and performs the relational epxression on them.
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env -- the environment in which to evaluate the node
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returns -- the evaluated value
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"""
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left_value = self.left.eval(env)
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right_value = self.right.eval(env)
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try:
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return operators[self.op](left_value, right_value)
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except KeyError:
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raise RuntimeError('unknown operator: ' + self.op)
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class AndExp(BooleanExp):
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"""The AST node for and expressions"""
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def __init__(self, left, right):
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"""
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The initializer method.
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left -- the left operand
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right -- the right operand
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"""
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self.left = left
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self.right = right
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def __repr__(self):
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"""
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A representation of the node for debug purposes.
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returns -- a String of the form "AndExp(left, right)"
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"""
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return 'AndExp(%s, %s)' % (self.left, self.right)
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def eval(self, env):
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"""
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Evaluates the node. Evaluates the left and right operands
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and performs a logical and on them.
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Supports short circuiting of logic.
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env -- the environment in which to evaluate the node
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returns -- the evaluated value
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"""
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return self.left.eval(env) and self.right.eval(env)
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class OrExp(BooleanExp):
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"""The AST node for or expressions"""
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def __init__(self, left, right):
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"""
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The initializer method.
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left -- the left operand
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right -- the right operand
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"""
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self.left = left
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self.right = right
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def __repr__(self):
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"""
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A representation of the node for debug purposes.
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returns -- a String of the form "OrExp(left, right)"
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"""
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return 'OrExp(%s, %s)' % (self.left, self.right)
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def eval(self, env):
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"""
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Evaluates the node. Evaluates the left and right operands
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and performs a logical or on them.
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Supports short circuiting of logic.
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env -- the environment in which to evaluate the node
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returns -- the evaluated value
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"""
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return self.left.eval(env) or self.right.eval(env)
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class NotExp(BooleanExp):
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"""The AST node for not expressions"""
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def __init__(self, exp):
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"""
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The initializer method.
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exp -- the operand to negate
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"""
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self.exp = exp
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def __repr__(self):
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"""
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A representation of the node for debug purposes.
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returns -- a String of the form "NotExp(operand)"
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"""
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return 'NotExp(%s)' % self.exp
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def eval(self, env):
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"""
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Evaluates the node. Evaluates the operand and performs a
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logical not on it.
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env -- the environment in which to evaluate the node
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returns -- the evaluated value
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"""
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return not self.exp.eval(env)
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class AssignStatement(Statement):
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"""The AST node for assignments"""
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def __init__(self, name, rexp):
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"""
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The initialization method.
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name -- the variable name
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rexp -- the expression that evaluates to the name
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"""
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self.name = name
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self.rexp = rexp
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def __repr__(self):
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"""
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A representation of the node for debug purposes.
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returns -- a String of the form "AssignStatement(name, expression)"
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"""
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return 'AssignStatement(%s, %s)' % (self.name, self.rexp)
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def eval(self, env):
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"""
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Evaluates the node. Evaluates the statement
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for the expression and saves it within the
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environment (under the given name).
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env -- the environment in which to evaluate the node
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"""
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env[self.name] = self.rexp.eval(env)
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class CompoundStatement(Statement):
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"""The AST node for compound statements"""
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def __init__(self, first, second):
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"""
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The initialization method.
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first -- the first statement
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second -- the second statement
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"""
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self.first = first
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self.second = second
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def __repr__(self):
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"""
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A representation of the node for debug purposes.
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returns -- a String of the form "CompoundStatement(first, second)"
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"""
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return 'CompoundStatement(%s, %s)' % (self.first, self.second)
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def eval(self, env):
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"""
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Evaluates the node. Evaluates the statements
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one after the other.
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env -- the environment in which to evaluate the node
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"""
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self.first.eval(env)
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self.second.eval(env)
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class IfStatement(Statement):
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"""The AST node for if statements"""
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def __init__(self, condition, on_true, on_false):
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"""
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The initialization method.
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condition -- the condition that needs to be evaluated
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on_true -- the statement that is to be executed when
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the condition is met
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on_false -- the statement that is to be executed when
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the condition is not met
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"""
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self.condition = condition
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self.on_true = on_true
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self.on_false = on_false
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def __repr__(self):
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"""
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A representation of the node for debug purposes.
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returns -- a String of the form "IfStatement(condition, on_true, on_false)"
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"""
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return 'IfStatement(%s, %s, %s)' % (self.condition, self.on_true, self.on_false)
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def eval(self, env):
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"""
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Evaluates the node. Evaluates the condition.
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If it is met, the on_true block is executed.
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If not and the on_false block exists, it is executed.
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env -- the environment in which to evaluate the node
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"""
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if self.condition.eval(env):
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self.on_true.eval(env)
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else:
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if self.on_false:
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self.on_false.eval(env)
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class WhileStatement(Statement):
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"""The AST node for while statements"""
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def __init__(self, condition, body):
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"""
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The initialization method.
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condition -- the condition that needs to be evaluated
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body -- the statement that is to be executed while
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the condition is met
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"""
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self.condition = condition
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self.body = body
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def __repr__(self):
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"""
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A representation of the node for debug purposes.
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returns -- a String of the form
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"WhileStatement(condition, body)"
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"""
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return 'WhileStatement(%s, %s)' % (self.condition, self.body)
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def eval(self, env):
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"""
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Evaluates the node. Evaluates the condition.
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While it is met, the body block is executed.
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env -- the environment in which to evaluate the node
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"""
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while self.condition.eval(env):
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self.body.eval(env)
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