Add tilde expansion as a string before symbols are parsed

[mnewt]

Work in progress

The idea is to parse the string straight from readline and make modifications before the reader touches it. A basic assumption is that we want to expand all tildes outside of parens but leave everything inside parens untouched. This seems to me to be what a user would expect.

Examples:

$ echo ~
/Users/user
$ echo ~ (str "hi ~") "~"
/Users/user hi ~ /Users/user
$ echo "\~"
~

@dundalek I have some questions for you:

• [ ] I like the elegance of closh's symbol parsing, but there are some features (like tilde, and probably more advanced variable and command substitution) where it's not really suited. Do you think this string-based approach is the best way forward or do you have a different idea? To me, this is definitely a compromise, but it seems like the right compromise between letting clojure do all the parsing and writing a whole parser just for closh.
• [ ] Is handle-line the right place from which to do this? Is that going to be in the code path in all scenarios where we want tildes expanded?
• [ ] Will the original expand-tilde ever be successfully called? Should it be factored out?

TODO:

• [ ] Add tests
• [ ] Add docs

[mnewt]

Addresses #8

[dundalek]

I think a proper parser is a way to go. I haven't looked too deeply into this yet. If we could extend the clojure reader that would the best. Otherwise some hybrid approach to have parser for the command mode and hand the the clojure parts to the reader.

I think the string based approaches might not be viable. It is not hard to come up with counter examples which blow up like: echo (str "(") ~.

I've been collecting forms that are broken and would be fixed by improved reader, I created an issue so where we can track it https://github.com/dundalek/closh/issues/39

[mnewt]

Withdrawing this in favor of a more considered approach