To decide if an excerpt of text is a value referred to notationally rather than by name.

§1. The nonterminal <s-literal> matches any literal, and on success produces an rvalue specification for the given value. Note that not every constant is a literal: names of objects, or of rules, for example, are not literals but they are certainly constants.

Note also that ordinal numbers are not valid as literals: "2nd" is not a noun. 

<s-literal> ::=
    <cardinal-number> |                    ==> { -, Rvalues::from_int(R[1], W) }
    minus <cardinal-number> |              ==> { -, Rvalues::from_int(-R[1], W) }
    hexadecimal <hexadecimal-number> |     ==> { -, Rvalues::from_int(R[1], W) }
    binary <binary-number> |               ==> { -, Rvalues::from_int(R[1], W) }
    octal <octal-number> |                 ==> { -, Rvalues::from_int(R[1], W) }
    <quoted-text> ( <response-letter> ) |  ==> { -, Rvalues::from_wording(W) }
    <quoted-text> |                        ==> { -, Rvalues::from_wording(W) }
    <s-literal-real-number> |              ==> { pass 1 }
    <s-literal-truth-state> |              ==> { pass 1 }
    <s-literal-list> |                     ==> { pass 1 }
    unicode <s-unicode-character> |        ==> { pass 1 }
    <s-literal-time> |                     ==> { pass 1 }
    <s-literal-unit-notation>              ==> { pass 1 }

§2. Response letters A to Z mark certain texts as being responses. These are only meaningful (and allowed) in the body of rules, but are syntactically valid as literals anywhere. 

<response-letter> internal 1 {
    inchar32_t *p = Lexer::word_raw_text(Wordings::first_wn(W));
    if ((p) && (p[0] >= 'A') && (p[0] <= 'Z') && (p[1] == 0)) {
        ==> { (int) (p[0]-'A'), - };
        return TRUE;
    }
    ==> { fail nonterminal };
}

§3. It might seem odd that the truth states count as literals, whereas names of instances of other kinds (people, say) do not. The argument for this is that there are always necessarily exactly two truth states, whereas there could in principle be any number of people, colours, vehicles, and such. 

<s-literal-truth-state> ::=
    false |  ==> { -, Rvalues::from_boolean(FALSE, W) }
    true     ==> { -, Rvalues::from_boolean(TRUE, W) }

§4. And these are the number-base literals: 

<hexadecimal-number> internal 1 {
    inchar32_t *p = Lexer::word_raw_text(Wordings::first_wn(W));
    inter_ti base = 16;
    Parse a literal in this number base4.1;
}

<octal-number> internal 1 {
    inchar32_t *p = Lexer::word_raw_text(Wordings::first_wn(W));
    inter_ti base = 8;
    Parse a literal in this number base4.1;
}

<binary-number> internal 1 {
    inchar32_t *p = Lexer::word_raw_text(Wordings::first_wn(W));
    inter_ti base = 2;
    Parse a literal in this number base4.1;
}

§4.1. Parse a literal in this number base4.1 = 

    int i = 0;
    inter_ti t = 0;
    while (p[i]) {
        inchar32_t c = p[i], d = 0;
        if ((c >= '0') && (c <= '9')) d = c - '0';
        else if ((c >= 'a') && (c <= 'f')) d = c - 'a' + 10;
        else if ((c >= 'A') && (c <= 'F')) d = c - 'A' + 10;
        else {
            ==> { fail nonterminal };
        }
        if (d >= base) {
            ==> { fail nonterminal };
        }
        t = t*base + (inter_ti) d;
        i++;
    }
    ==> { (int) t, - };
    return TRUE;