Implement replacements for Python statements.

[gilch]

I've already done most of the work in Drython. I think I'll just copy the relevant bits over, but this may become a separate package later.

These will be special cased in the Hebigo reader because they're Python reserved words, e.g. the symbol def would munge as hebi.basic.._macro_.def_.

def is an especially important one. I'm thinking roughly Scheme semantics:

So in Hebigo,

def: key value

assigns a simple global.

But

def: name: arg1 arg2 : kw1 default1
    "docstring"
    body...

defines a function. It should compile to Hissp like:

('hebi.basic.._macro_.def_', ('name', 'arg1', 'arg2', ':', 'kw1', 'default1'),
    ('quote', 'docstring', {'str': True}),
    body...

[gilch]

Try statements are also important. Control statements less (we have higher-order functions), but still high priority if we don't want to scare of Pythonistas. Drython pretty much has these down. It's just a matter of adding macros to make them easy.

I'm not sure how classes should work yet.

async and yield look difficult. Drython doesn't have good replacements. Fortunately, they're not used as much.

[gilch]

I started an experimental branch for this. I think the munging is working. I've also got an implementation for def, but I'll need #5 to test it properly. I ended up writing the macro in readerless mode. It's certainly doable without using Lissp, although that was also an option.

[gilch]

def: appears to be working now. For proper tests we also want from:/import: and class: macros. Python has a lot of import variations. This doesn't look simple.

[gilch]

from: and import: macros are now available. They probably need more thorough tests, but this might happen naturally as they are used. Syntax resembles Python's as closely as Hebigo's grammar can manage.

import: foo bar.baz
from: spam.ham :import eggs sausage :as saus

[gilch]

The critical macros are all implemented and working well enough to write native unit tests cases. They still need some work on certain edge cases (need more tests!) and don't quite get the metadata right.

[gilch]

I just added del and this is pretty much done now. We're still missing while. I'm on the fence on that one. !loop seems better. yield/async/await look difficult #11. return is probably not happening, Clojure and Scheme seem to get along fine without it. (Although it could be done with exceptions, like break is. See Drython.)