text-based Snap!

having some fun with the new metaprogramming features

write a snap block at the prompt:
group sub-expressions (including variables, and boolean/number parameters) with parentheses;
rings go in curly braces;
quote strings with single quotes;
booleans are just called true and false;
lists look like [1, 2, 3]

use up and down keys for history, press insert to paste, compose or otherwise insert text

this is probably still really buggy

TODO:
- support multiple statements per expression/ring with semicolon
- serialise rings back to text properly