exception.py

class SchemeError(Exception):
    pass

# Unbound variable
class UnboundVariableError(SchemeError):
    def __init__(self, var):
        self.msg = "Unbound variable {0}".format(var)

# IllegalArgumentErrors
class IllegalArgumentError(SchemeError):
    pass

# Bad number of arguments
class ArgumentCountError(IllegalArgumentError):
    def __init__(self, function, expected, given):
        self.msg = "Bad number of arguments: {0} takes {1} arguments ({2} given)".format(function, expected, given)

# Wrong type of argument
class WrongArgumentTypeError(IllegalArgumentError):
    def __init__(self, function, expected, given):
        self.msg = "Wrong type of argument for {0}: Expected {1} ({2} given)".format(function, expected, given)

# Index out of bounds
class IndexOutOfBoundsError(SchemeError):
    def __init__(self, vector, index, length):
        self.msg = "Index out of bounds: Tried to access index {1} of {0} (with length {2})".format(vector, index, length)

# Mismatched Parens
class MismatchedParensError(SchemeError):
    def __init__(self, expression):
        self.msg = "Mismatched parenthesis: {0}".format(expression)

# Parse Error
class ParseError(SchemeError):
    def __init__(self, token):
        self.msg = "Error: Unidentified token {0}".format(token)

# Trace Error
class TraceError(SchemeError):
    def __init__(self, expression, reason):
        self.msg = "Error: Cannot trace {0}: {1}".format(expression, reason)

# Untrace Error
class UntraceError(SchemeError):
    def __init__(self, expression, reason):
        self.msg = "Error: Cannot untrace {0}: {1}".format(expression. reason)