Optimize and/or

[gilch]

Depends on #824.
Related #842.

Even in the case that and/or contains a statement, it may have several expressions in a row that don't need to be converted to if branches. Hy could avoid redundant assignments by keeping those runs as expressions and only assigning the result to an anonymous variable.

For example:

=> (print (and 1 2 3 (setv x 1) 4 5 6))
_hy_anon_var_1 = 1 and 2 and 3
if _hy_anon_var_1:
    x = 1
    _hy_anon_var_1 = x and 4 and 5 and 6
print(_hy_anon_var_1)
6

[gilch]

For comparison, this is what Hy is doing currently to the above example. (#824 has been merged)

=> (print (and 1 2 3 (setv x 1) 4 5 6))
_hy_anon_var_1 = 1
if _hy_anon_var_1:
    _hy_anon_var_1 = 2
    if _hy_anon_var_1:
        _hy_anon_var_1 = 3
        if _hy_anon_var_1:
            x = 1
            _hy_anon_var_1 = x
            if _hy_anon_var_1:
                _hy_anon_var_1 = 4
                if _hy_anon_var_1:
                    _hy_anon_var_1 = 5
                    if _hy_anon_var_1:
                        _hy_anon_var_1 = 6
print(_hy_anon_var_1)
6

Notice there are eight assignments, but the optimized version only needs three.