main = set T = 'foobar' &
       print T &
       expect_chars(T).

# Given a single-character string, return call(prodref('$', 'expect'), S)
# Given a string, return and(call(prodref('$', 'expect'), head(S)),
#                            expect_chars(tail(S))).

expect_chars(S) = print S & expect_chars_r @ S.
expect_chars_r = any → C &
  set E = call(prodref('$', 'expect'), list(atom(C), nil)) &
  ((eof & return E) | (expect_chars_r → R & return and(E, R))).