An experiment to create the analog of Haskell's Parsec library not on
the basis of monads, but in ANSI CL, using the signal protocol,
special variables and macros.

Different test-cases are gathered in examples/.

A note on terminology: these parsers are generic and can (in theory)
work on other objects, than characters.  Those objects could be called
tokens, but this name is quite heavily used in parsers, so not to
create confusion a different term is used: `items'.

Example usage with the parser, defined in examples/better-veselov.lisp:

CL-USER> (with-input-from-string (in "1 + 2-10 ^ ac1(ac+f(),2)")
           (parse in 'expression))
((:ATOM "1") (:OP #\+) (:ATOM "2") (:OP #\-) (:ATOM "10") (:OP #\^)
 (:FUNC "ac1" ((:ATOM "ac") (:OP #\+) (:FUNC "f")) ((:ATOM "2"))))

CL-USER> (with-input-from-string (in "1 + 2-10 ^ ac1(")
           (parse in 'expression))
=> Parse error.  Error stack: ((EXPRESSION) (EOF))

Caution: not ready for production use.�