Closures about seq HOT 2 CLOSED

OK I have an idea for this that hijacks partial function applications. Consider this case:

def f(a):
    def g(b):  # NOT a regular function, but a closure
        return a + b
    return g

We can transform it to:

def f(a):
    def _g(b, a):  # 'a' captured from enclosing scope; now it's just a plain function
        return a + b
    g = _g(..., a)  # partial function application
    return g

The reason we have to do something like this is because g is not a regular function here; it is really a combination of a function and the value of a that gets passed to f (i.e. the object returned by f needs to be different on each invocation, to account for the fact that a can be different). We solve this problem already for partial functions though, so maybe we can just use it.

from seq.

Implemented in #132

from seq.