Python parser.parse函数代码示例

def test_calling_atom_raises_exception():
    """A function call to a non-function should result in an error."""

    with assert_raises_regexp(LispError, "not a function"):
        evaluate(parse("(#t 'foo 'bar)"), Environment())
    with assert_raises_regexp(LispError, "not a function"):
        evaluate(parse("(42)"), Environment())

def test_calling_with_wrong_number_of_arguments():
    """Functions should raise exceptions when called with wrong number of arguments."""

    env = Environment()
    evaluate(parse("(define fn (lambda (p1 p2) 'whatever))"), env)
    error_msg = "wrong number of arguments, expected 2 got 3"
    with assert_raises_regexp(LispError, error_msg):
        evaluate(parse("(fn 1 2 3)"), env)

def test_parse_exception_extra_paren():
    """Another exception is raised if the expression is too large.

    The parse function expects to receive only one single expression. Anything
    more than this, should result in the proper exception."""

    with assert_raises_regexp(LispError, 'Expected EOF'):
        parse('(foo (bar x y)))')

def test_parse_boolean():
    """Parsing single booleans.

    Booleans are the special symbols #t and #f. In the ASTs they are represented
    by Pythons True and False, respectively. """

    assert_equals(True, parse('#t'))
    assert_equals(False, parse('#f'))

def test_lambda_arguments_are_lists():
    """The parameters of a `lambda` should be a list."""

    closure = evaluate(parse("(lambda (x y) (+ x y))"), Environment())
    assert_true(is_list(closure.params))

    with assert_raises(LispError):
        evaluate(parse("(lambda not-a-list (body of fn))"), Environment())

def test_checking_whether_list_is_empty():
    """The `empty` form checks whether or not a list is empty."""

    assert_equals(False, evaluate(parse("(empty '(1 2 3))"), Environment()))
    assert_equals(False, evaluate(parse("(empty '(1))"), Environment()))

    assert_equals(True, evaluate(parse("(empty '())"), Environment()))
    assert_equals(True, evaluate(parse("(empty (tail '(1)))"), Environment()))

def test_creating_longer_lists_with_only_cons():
    """`cons` needs to evaluate it's arguments.

    Like all the other special forms and functions in our language, `cons` is
    call-by-value. This means that the arguments must be evaluated before we
    create the list with their values."""

    result = evaluate(parse("(cons 3 (cons (- 4 2) (cons 1 '())))"), Environment())
    assert_equals(parse("(3 2 1)"), result)

def test_parse_integer():
    """Parsing single integer.

    Integers are represented in the ASTs as Python ints.

    Tip: String objects have a handy .isdigit() method.
    """

    assert_equals(42, parse('42'))
    assert_equals(1337, parse('1337'))

def test_call_to_function_should_evaluate_arguments():
    """Call to function should evaluate all arguments.

    When a function is applied, the arguments should be evaluated before being bound
    to the parameter names."""

    env = Environment()
    closure = evaluate(parse("(lambda (a) (+ a 5))"), env)
    ast = [closure, parse("(if #f 0 (+ 10 10))")]

    assert_equals(25, evaluate(ast, env))

def test_math_operators_only_work_on_numbers():
    """The math functions should only allow numbers as arguments."""

    with assert_raises(LispError):
        evaluate(parse("(+ 1 'foo)"), Environment())
    with assert_raises(LispError):
        evaluate(parse("(- 1 'foo)"), Environment())
    with assert_raises(LispError):
        evaluate(parse("(/ 1 'foo)"), Environment())
    with assert_raises(LispError):
        evaluate(parse("(mod 1 'foo)"), Environment())

def test_creating_lists_by_quoting():
    """One way to create lists is by quoting.

    We have already implemented `quote` so this test should already be
    passing.

    The reason we need to use `quote` here is that otherwise the expression would
    be seen as a call to the first element -- `1` in this case, which obviously isn't
    even a function."""

    assert_equals(parse("(1 2 3 #t)"),
                  evaluate(parse("'(1 2 3 #t)"), Environment()))

def test_parse_list_of_symbols():
    """Parsing list of only symbols.

    A list is represented by a number of elements surrounded by parens. Python lists
    are used to represent lists as ASTs.

    Tip: The useful helper function `find_matching_paren` is already provided in
    `parse.py`.
    """

    assert_equals(['foo', 'bar', 'baz'], parse('(foo bar baz)'))
    assert_equals([], parse('()'))

def test_calling_very_simple_function_in_environment():
    """A call to a symbol corresponds to a call to its value in the environment.

    When a symbol is the first element of the AST list, it is resolved to its value in
    the environment (which should be a function closure). An AST with the variables
    replaced with its value should then be evaluated instead."""

    env = Environment()
    evaluate(parse("(define add (lambda (x y) (+ x y)))"), env)
    assert_is_instance(env.lookup("add"), Closure)

    result = evaluate(parse("(add 1 2)"), env)
    assert_equals(3, result)

def test_basic_if_statement():
    """If statements are the basic control structures.

    The `if` should first evaluate its first argument. If this evaluates to true, then
    the second argument is evaluated and returned. Otherwise the third and last argument
    is evaluated and returned instead."""

    if_expression = parse("(if #t 42 1000)")
    assert_equals(42, evaluate(if_expression, Environment()))
    if_expression = parse("(if #f 42 1000)")
    assert_equals(1000, evaluate(if_expression, Environment()))
    if_expression = parse("(if #t #t #f)")
    assert_equals(True, evaluate(if_expression, Environment()))

def test_evaluating_eq_function():
    """The `eq` form is used to check whether two expressions are the same atom."""

    assert_equals(True, evaluate(["eq", 1, 1], Environment()))
    assert_equals(False, evaluate(["eq", 1, 2], Environment()))

    # From this point, the ASTs might sometimes be too long or cummbersome to
    # write down explicitly, and we'll use `parse` to make them for us.
    # Remember, if you need to have a look at exactly what is passed to `evaluate`,
    # just add a print statement in the test (or in `evaluate`).

    assert_equals(True, evaluate(parse("(eq 'foo 'foo)"), Environment()))
    assert_equals(False, evaluate(parse("(eq 'foo 'bar)"), Environment()))

    # Lists are never equal, because lists are not atoms
    assert_equals(False, evaluate(parse("(eq '(1 2 3) '(1 2 3))"), Environment()))