Descriptions such as "open door" or "number which is greater than 8" which may or may not be true of any given rvalue at run-time.

• §1. Descriptions vs propositions
• §3. Descriptions vs kinds
• §5. Descriptions vs instances
• §6. Descriptions vs constants
• §7. Testing
• §8. Adjectives
• §9. Quantification
• §10. Callings
• §11. Pretty-printing
• §12. Comparing

§1. Descriptions vs propositions. A description of \(K\)-values is stored as a TEST_VALUE_NT node with a constant node beneath it of kind "description of \(K\)". This in turn will hold a logical proposition \(\phi(x)\) with one free variable \(x\) expected to range over \(K\).

parse_node *Descriptions::from_proposition?Usage of Descriptions::from_proposition:
§3, §5
Constants and Descriptions - §8, §10, §18.1.1
Verbal and Relative Clauses - §6.1, §11.4(pcalc_prop *prop, wording W) {
    parse_node *spec = Node::new_with_words(TEST_VALUE_NT, W);
    spec->down = Rvalues::constant_description(prop, W);
    return spec;
}

pcalc_prop *Descriptions::to_proposition?Usage of Descriptions::to_proposition:
§3, §4, §5, §6, §7, §8, §9, §10, §12.1
Specifications - §4
Dash - §24(parse_node *spec) {
    if ((Specifications::is_description(spec)) || (Node::is(spec, TEST_VALUE_NT))) {
        spec = spec->down;
    } else {
        LOG("Spec: $T\n", spec);
        internal_error("tried to extract proposition from non-description");
    }
    if (Rvalues::is_CONSTANT_construction(spec, CON_description))
        return Specifications::to_proposition(spec);
    return NULL;
}

pcalc_prop *Descriptions::to_unbound_proposition(parse_node *spec) {
    pcalc_prop *prop = Descriptions::to_proposition(spec);
    if (prop) prop = Binding::unbind(prop);
    return prop;
}

§2. We are going to need to edit the proposition, using the following:

void Descriptions::set_proposition?Usage of Descriptions::set_proposition:
§3, §8, §9, §10(parse_node *spec, pcalc_prop *prop) {
    if (Specifications::is_description(spec)) spec = spec->down;
    else internal_error("tried to set proposition for non-description");
    if (Rvalues::is_CONSTANT_construction(spec, CON_description))
        Rvalues::set_constant_description_proposition(spec, prop);
    else internal_error("set domain proposition wrongly");
}

§3. Descriptions vs kinds. A kind is "composited" if it's derived from a word such as "something", which implies a quantifier as well as a kind.

parse_node *Descriptions::from_kind?Usage of Descriptions::from_kind:
Specifications - §1
Constants and Descriptions - §21(kind *K, int composited) {
    parse_node *spec = Descriptions::from_proposition(NULL, EMPTY_WORDING);
    if (K) {  a test made only for error recovery
        pcalc_prop *prop;
        if (composited)
            prop = KindPredicates::new_composited_atom(K, Terms::new_variable(0));
        else
            prop = KindPredicates::new_atom(K, Terms::new_variable(0));
        TypecheckPropositions::type_check(prop,
            TypecheckPropositions::tc_no_problem_reporting());
        Descriptions::set_proposition(spec, prop);
    }
    return spec;
}

kind *Descriptions::to_kind?Usage of Descriptions::to_kind:
Specifications - §1(parse_node *spec) {
    return Binding::infer_kind_of_variable_0(
        Descriptions::to_proposition(spec));
}

§4. Some descriptions explicitly name a kind ("even numbers"), others imply a kind but do so only implicitly ("scenery").

int Descriptions::makes_kind_explicit(parse_node *spec) {
    if ((Specifications::is_description(spec)) &&
        (Descriptions::explicit_kind(spec))) return TRUE;
    return FALSE;
}

kind *Descriptions::explicit_kind?Usage of Descriptions::explicit_kind:
§7, §10, §12.4(parse_node *spec) {
    return Propositions::describes_kind(Descriptions::to_proposition(spec));
}

§5. Descriptions vs instances. One is not allowed to form a description such as "the even 22", where adjectives are applied to a literal. But one is allowed to do so with a named object or similar, so:

parse_node *Descriptions::from_instance?Usage of Descriptions::from_instance:
Constants and Descriptions - §12(instance *I, wording W) {
    if (I == NULL) internal_error("description of null instance");
    parse_node *val = Rvalues::from_instance(I);
    pcalc_prop *prop = Atoms::prop_x_is_constant(val);
    TypecheckPropositions::type_check(prop,
        TypecheckPropositions::tc_no_problem_reporting());
    return Descriptions::from_proposition(prop, W);
}

instance *Descriptions::to_instance?Usage of Descriptions::to_instance:
Specifications - §5
Dash - §26(parse_node *spec) {
    if (Specifications::is_description(spec)) {
        pcalc_prop *prop = Descriptions::to_proposition(spec);
        parse_node *val = Propositions::describes_value(prop);
        if (val == NULL) return NULL;
        return Rvalues::to_instance(val);
    }
    return NULL;
}

§6. Descriptions vs constants. A description such as "even numbers" is normally represented as a description node, but sometimes we need to think of this as a noun and not a predicate. If so, we convert to a constant using the following. Note that we remove a universal quantifier: this is so that "even numbers", if read as "all even numbers", becomes rather "is an even number".

parse_node *Descriptions::to_rvalue?Usage of Descriptions::to_rvalue:
Dash - §18.3.1, §18.5.3(parse_node *spec) {
    if (Rvalues::is_CONSTANT_construction(spec, CON_description)) return spec;
    if (Specifications::is_description(spec) == FALSE) {
        LOG("$T\n", spec); internal_error("not a description");
    }
    pcalc_prop *prop = Propositions::copy(
        Descriptions::to_proposition(spec));
    if (prop) {
        prop = Propositions::trim_universal_quantifier(prop);
        if (Binding::number_free(prop) != 1)
            return NULL;  Specifications::new_UNKNOWN(Node::get_text(spec));
    }

    parse_node *con = Node::new(CONSTANT_NT);
    Node::set_kind_of_value(con,
        Kinds::unary_con(CON_description,
            Binding::infer_kind_of_variable_0(prop)));
    Node::set_proposition(con, prop);
    Node::set_text(con, Node::get_text(spec));
    return con;
}

§7. Testing. Descriptions are "qualified" when adjectives, or relative clauses, make them dependent on context. For instance, "a vehicle" is unqualified, but "an even number" or "a vehicle in Trafalgar Square" are qualified — the same value might satisfy the description at some times but not others during play.

int Descriptions::is_qualified?Usage of Descriptions::is_qualified:
Dash - §26(parse_node *spec) {
    if ((Specifications::is_description(spec)) &&
        ((Descriptions::is_complex(spec)) ||
            (Descriptions::number_of_adjectives_applied_to(spec) > 0)))
        return TRUE;
    return FALSE;
}

int Descriptions::is_kind_like?Usage of Descriptions::is_kind_like:
Specifications - §2(parse_node *spec) {
    if ((Specifications::is_description(spec)) &&
        (Propositions::length(Descriptions::to_proposition(spec)) == 1) &&
        (Descriptions::explicit_kind(spec)))
        return TRUE;
    return FALSE;
}

int Descriptions::is_complex?Usage of Descriptions::is_complex:
§12.1
Dash - §18.4, §18.6.2.1(parse_node *spec) {
    if (Specifications::is_description(spec))
        return Propositions::is_complex(
            Descriptions::to_proposition(spec));
    return FALSE;
}

int Descriptions::is_adjectives_plus_kind(parse_node *spec) {
    if (Specifications::is_description(spec)) {
        if (Descriptions::number_of_adjectives_applied_to(spec) == 0)
            return FALSE;
        kind *K = Descriptions::explicit_kind(spec);
        if (K) return TRUE;
    }
    return FALSE;
}

§8. Adjectives. Adjectives occurring in the proposition can be thought of as forming a list. It's sometimes convenient to loop through this list:

define LOOP_THROUGH_ADJECTIVE_LIST(au, au_prop, spec)
    for (au = Propositions::first_unary_predicate(
        Descriptions::to_proposition(spec), &au_prop);
        au;
        au = Propositions::next_unary_predicate(&au_prop))

int Descriptions::number_of_adjectives_applied_to?Usage of Descriptions::number_of_adjectives_applied_to:
§7, §12.3
Dash - §10.9.1.1.5.1.2(parse_node *spec) {
    return Propositions::count_adjectives(
        Descriptions::to_proposition(spec));
}

unary_predicate *Descriptions::first_unary_predicate?Usage of Descriptions::first_unary_predicate:
Dash - §10.9.1.1.5.1.2(parse_node *spec) {
    return Propositions::first_unary_predicate(
        Descriptions::to_proposition(spec), NULL);
}

void Descriptions::add_to_adjective_list?Usage of Descriptions::add_to_adjective_list:
Constants and Descriptions - §10, §11
Verbal and Relative Clauses - §6.1(unary_predicate *au, parse_node *spec) {
    pcalc_prop *prop = Descriptions::to_proposition(spec);
    adjective *aph = AdjectivalPredicates::to_adjective(au);
    int negated = FALSE;
    if (AdjectivalPredicates::parity(au) == FALSE) negated = TRUE;
    prop = Propositions::concatenate(prop,
        AdjectivalPredicates::new_atom_on_x(aph, negated));
    TypecheckPropositions::type_check(prop,
        TypecheckPropositions::tc_no_problem_reporting());
    Descriptions::set_proposition(spec, prop);
}

void Descriptions::add_to_adjective_list_w?Usage of Descriptions::add_to_adjective_list_w:
Constants and Descriptions - §11(unary_predicate *au, parse_node *spec) {
    quantifier *Q = Descriptions::get_quantifier(spec);
    int N = Descriptions::get_quantification_parameter(spec);
    pcalc_prop *prop = Descriptions::get_inner_prop(spec);
    adjective *aph = AdjectivalPredicates::to_adjective(au);
    int negated = FALSE;
    if (AdjectivalPredicates::parity(au) == FALSE) negated = TRUE;
    prop = Propositions::concatenate(prop,
        AdjectivalPredicates::new_atom_on_x(aph, negated));
    TypecheckPropositions::type_check(prop,
        TypecheckPropositions::tc_no_problem_reporting());
    Descriptions::set_proposition(spec, prop);
    if (Q) Descriptions::quantify(spec, Q, N);
}

§9. Quantification. For example, the "all" in "all of the open doors".

void Descriptions::quantify?Usage of Descriptions::quantify:
§8
Constants and Descriptions - §18.5, §21(parse_node *spec, quantifier *q, int par) {
    pcalc_prop *prop = Descriptions::to_proposition(spec);
    if (q != exists_quantifier)
        prop = Propositions::concatenate(Atoms::new(DOMAIN_OPEN_ATOM), prop);
    prop = Propositions::concatenate(Atoms::QUANTIFIER_new(q, 0, par), prop);
    if (q != exists_quantifier)
        prop = Propositions::concatenate(prop, Atoms::new(DOMAIN_CLOSE_ATOM));
    Descriptions::set_proposition(spec, prop);
    TypecheckPropositions::type_check(prop, TypecheckPropositions::tc_no_problem_reporting());
}

pcalc_prop *Descriptions::get_inner_prop?Usage of Descriptions::get_inner_prop:
§8(parse_node *spec) {
    pcalc_prop *prop = Descriptions::to_proposition(spec);
    if ((prop) && (Atoms::get_quantifier(prop))) {
        prop = Propositions::copy(prop);
        prop = Propositions::ungroup_after(prop, prop, NULL);
        return prop->next;
    }
    return SentencePropositions::from_spec(spec);
}

pcalc_prop *Descriptions::get_quantified_prop(parse_node *spec) {
    pcalc_prop *prop = Descriptions::to_proposition(spec);
    if ((prop) && (Atoms::get_quantifier(prop)) &&
        (Atoms::get_quantification_parameter(prop) > 0)) {
        prop = Propositions::copy(prop);
        prop = Propositions::ungroup_after(prop, prop, NULL);
        return prop->next;
    }
    return SentencePropositions::from_spec(spec);
}

quantifier *Descriptions::get_quantifier?Usage of Descriptions::get_quantifier:
§8
Dash - §10.9.1.2.3.3, §18.5.3(parse_node *spec) {
    if (Specifications::is_description(spec))
        return Atoms::get_quantifier(Descriptions::to_proposition(spec));
    return NULL;
}

int Descriptions::get_quantification_parameter?Usage of Descriptions::get_quantification_parameter:
§8(parse_node *spec) {
    if (Specifications::is_description(spec))
        return Atoms::get_quantification_parameter(Descriptions::to_proposition(spec));
    return 0;
}

§10. Callings. For example, "the neighbour" in "a room which is adjacent to a lighted room (called the neighbour)".

void Descriptions::attach_calling?Usage of Descriptions::attach_calling:
Constants and Descriptions - §18.4(parse_node *spec, wording C) {
    kind *K = Descriptions::explicit_kind(spec);
    pcalc_prop *prop = Descriptions::to_proposition(spec);
    prop = Propositions::concatenate(
        prop,
        CreationPredicates::calling_up(C, Terms::new_variable(0), K));
    TypecheckPropositions::type_check(prop, TypecheckPropositions::tc_no_problem_reporting());
    Descriptions::set_proposition(spec, prop);
}

wording Descriptions::get_calling(parse_node *spec) {
    if (Specifications::is_description(spec))
        for (pcalc_prop *pp = Descriptions::to_proposition(spec); pp; pp = pp->next)
            if (CreationPredicates::is_calling_up_atom(pp))
                return CreationPredicates::get_calling_name(pp);
    return EMPTY_WORDING;
}

void Descriptions::clear_calling(parse_node *spec) {
    if (spec == NULL) return;
    pcalc_prop *pp, *prev_pp = NULL;
    for (pp = Descriptions::to_proposition(spec); pp; prev_pp = pp, pp = pp->next)
        if (CreationPredicates::is_calling_up_atom(pp)) {
            Descriptions::set_proposition(spec,
                Propositions::delete_atom(
                    Descriptions::to_proposition(spec), prev_pp));
            return;
        }
}

int Descriptions::makes_callings(parse_node *spec) {
    if (spec == NULL) return FALSE;
    if (Specifications::is_description(spec)) {
        if (CreationPredicates::contains_callings(Descriptions::to_proposition(spec)))
            return TRUE;
        wording C = Descriptions::get_calling(spec);
        if (Wordings::nonempty(C)) return TRUE;
    }
    return FALSE;
}

§11. Pretty-printing.

void Descriptions::write_out_in_English?Usage of Descriptions::write_out_in_English:
Conditions - §11(OUTPUT_STREAM, parse_node *spec) {
    kind *K = Specifications::to_kind(spec);
    WRITE("a description");
    if (K) {
        wording KW = Kinds::Behaviour::get_name(K, TRUE);
        if (Wordings::nonempty(KW)) WRITE(" of %+W", KW);
    }
}

§12. Comparing. Descriptions are used to set out the domain of rules, and rules have to be sorted in order of narrowness, which means we need a way to tell which is narrower of two descriptions.

int Descriptions::compare_specificity?Usage of Descriptions::compare_specificity:
Specifications - §9(parse_node *spec1, parse_node *spec2) {
    If either of these two descriptions has a complex proposition, then propositional size decides it12.1;
    If the typechecker recognises one as properly within the other, then that's the more specific12.2;
    If either of these two descriptions have adjectives, adjective count decides it12.3;
    If both descriptions specify a kind, kind inheritance decides it12.4;
    return 0;
}

§12.1. Which of two propositions is more specific? To perform that test perfectly, we would need a way to determine, given two propositions A and B, whether one implied the other or not. Since predicate calculus is complete, and our domains are mostly finite, there do in fact exist (slow and difficult) algorithms which could determine this. But there would be real problems with larger domains not amenable to model-checking, such as "number", and anyway — why not cheat?

Proposition length is admittedly a crude measure, but because of the fact that both propositions have come from the same generative algorithm, it does indeed turn out that \(A\Rightarrow B\) means \(\ell(A) \geq \ell(B)\), where \(\ell\) is the number of atoms in the proposition. So we simply use it as a sorting key.

If either of these two descriptions has a complex proposition, then propositional size decides it12.1 =

    int comp1 = Descriptions::is_complex(spec1);
    int comp2 = Descriptions::is_complex(spec2);
    if ((comp1) || (comp2)) {
        if (comp2 == FALSE) return 1;
        if (comp1 == FALSE) return -1;
        int len1 = Propositions::length(Descriptions::to_proposition(spec1));
        int len2 = Propositions::length(Descriptions::to_proposition(spec2));
        if ((len1 > 0) || (len2 > 0)) {
            LOGIF(SPECIFICITIES,
                "Test %d: Comparing specificity of props:\n(%d) $D\n(%d) $D\n",
                cco, len1, Descriptions::to_proposition(spec1), len2, Descriptions::to_proposition(spec2));
        }
        if (len1 > len2) return 1;
        if (len1 < len2) return -1;
    }

• This code is used in §12.

§12.2. If the typechecker recognises one as properly within the other, then that's the more specific12.2 =

    if (Dash::compatible_with_description(spec1, spec2) == ALWAYS_MATCH) {
        if (Dash::compatible_with_description(spec2, spec1) != ALWAYS_MATCH) return 1;
    } else {
        if (Dash::compatible_with_description(spec2, spec1) == ALWAYS_MATCH) return -1;
    }

• This code is used in §12.

§12.3. If either of these two descriptions have adjectives, adjective count decides it12.3 =

    int count1 = Descriptions::number_of_adjectives_applied_to(spec1);
    int count2 = Descriptions::number_of_adjectives_applied_to(spec2);
    if (count1 > count2) return 1;
    if (count1 < count2) return -1;

• This code is used in §12.

§12.4. If both descriptions specify a kind, kind inheritance decides it12.4 =

    kind *k1 = Descriptions::explicit_kind(spec1);
    kind *k2 = Descriptions::explicit_kind(spec2);
    if ((k1) && (k2)) {
        if (Kinds::ne(k1, k2)) {
            if (Kinds::conforms_to(k1, k2)) return 1;
            if (Kinds::conforms_to(k2, k1)) return -1;
        }
    }

• This code is used in §12.