empty ::=
        => [ t ]
end ::= 
        ~<anything>
exactly :want ::=
        <anything>:got ?[ (equal want got) ] => [ want ]
ochar ::=
        <anything>:x ?[ (characterp x) ] => [ x ]
ospace ::= 
        <ochar>:x ?[ (<= (char-code x) 32) ] => [ x ]
spaces ::=
        <ospace>*
letter ::=
        <ochar>:x ?[ (alpha-char-p x) ] => [ x ]
digit ::=
        <ochar>:x ?[ (digit-char-p x) ] => [ x ]