TODO

- Maybe separate special forms into a parsing and an evaluating section and store them in modules with a dictionary
- Clean up hacky imperative code ("let mutable x = ...")
- Clean up list building (use cons with List.rev instead of xs <- xs @ [...])
- Fix expr.ToString()
- Add basic typechecking to builtins
- Structs? (just scheme-like; defstruct foo is x y end define bar new foo foo-set-x bar 5 print foo-x bar)
- s?printf (how to implement this with fixed arity? lists or special form that parses the format string?)
- For loop iterators (for expr in expr do ... end - e.g. for i in list-range 1 5 do print i end could eventually end up with list comprehension syntax like for x is * i 2 in ... end)
- While loops
- Maybe + on strings and lists for concatenation?
- Dictionaries
- set-car and set-cdr
- Unit testing? Maybe?
- Functions: include, assert, lambda
- Fix stream-read-all for sockets
- Rename define to something more concise (def, let, var, val, etc)
- Tail call optimization
- Builtins should use "match args with | [a; b; c]" syntax instead of addressing by index
- Builtins should have a type signature as a comment (e.g. // stream-close stream -> nil)
- High order functions should be supported (maybe an apply function)

Modules that should be in stdlib:
- text
  done:
    regex-match
    string-split
    substring
  todo:
    regex-search
    regex-replace
    string-replace
    string-reverse
    string-repeat
    lines
    unlines
    string-find

- stream
  done:
    socket-open
    file-open
    stream-close
    stream-{read,write}
    stream-read-all
    stream-read-line
  todo:
    stream-{read,write}-u?int{8,16,32,64}
    stream-status
    socket-listen
    socket-accept

- http
  todo:
    http-get
    http-post

- list
  done:
    list-reverse
    list-append
  todo:
    ca+dr
    cd+r
    caadr
    list-repeat
    list-length
    list-splice
    list-range
    list-concat
    map
    zip
    filter
    reduce