polymorphic input - aka lexing

[ylixir]

we should allow more than just strings as input.

this will allow stratifying our parsing. so we could make one parser that lexes a string, and then a second parser that parses the tokens from the lexer into an ast

maybe even go farther and implement micropass compilers etc.

[ylixir]

perhaps we could add "streaminterface" iterators that implement pop and lit. then the parser combinators could be bootstrapped with the stream primitives.