nillang, only accepts nil
nillang with parser
parse booleans, initial type hierarchy
parse ints and floats
parse string
parse symbol
as you can see symbols aren't resolved
implement eval passing env, resolve symbols

introduce error hierarchy
add examples eval'ing symbols
parse empty list
parse pairs
support line comments
move types to ptypes, move eval to use cc
implement Applicative and one fn (display), eval pairs as fun calls
implement operatives
add lambda type and lambda operative
implement do operative, wrap input in implicit do
add def operative (and length caching for pairs)
implement call/cc
implement arithmetic and logic operatives