1 

     2 assert(der('a', ZERO | ONE) == (ZERO | ZERO))

     3 assert(der('a', (CHAR('a') | ONE) ~ CHAR('a')) == ALT((ONE | ZERO) ~ CHAR('a'), ONE))

     4 assert(der('a', (CHAR('a') | CHAR('a')) ~ CHAR('a')) == (ONE | ONE) ~ CHAR('a'))

     5 assert(der('a', STAR(CHAR('a'))) == (ONE ~ STAR(CHAR('a'))))

     6 assert(der('b', STAR(CHAR('a'))) == (ZERO ~ STAR(CHAR('a'))))

     7 

     8 

     9 val r0_urban = "a" ~ "b" ~ "c"

    10 assert(der('a', r0_urban) == (ONE ~ "b") ~ "c")

    11 assert(der('b', r0_urban) == (ZERO ~ "b") ~ "c")

    12 assert(der('c', r0_urban) == (ZERO ~ "b") ~ "c")

    13 

    14 val r1_urban = (ONE ~ "b") ~ "c"

    15 

    16 assert(der('a', r1_urban) == ((ZERO ~ "b") | ZERO) ~ "c")

    17 assert(der('b', r1_urban) == ((ZERO ~ "b") | ONE) ~ "c")

    18 assert(der('c', r1_urban) == ((ZERO ~ "b") | ZERO) ~ "c")

    19 

    20 val r2_urban = ((ZERO ~ "b") | ONE) ~ "c"

    21 

    22 assert(der('a', r2_urban) == ((((ZERO ~ "b") | ZERO) ~ "c") | ZERO))

    23 assert(der('b', r2_urban) == ((((ZERO ~ "b") | ZERO) ~ "c") | ZERO))

    24 assert(der('c', r2_urban) == ((((ZERO ~ "b") | ZERO) ~ "c") | ONE))