Inform 6 Code

To generate I6 routines of imperative code.

§1.

void I6TargetCode::create_generator(code_generator *gtr) {
    METHOD_ADD(gtr, DECLARE_FUNCTION_MTID, I6TargetCode::declare_function);
    METHOD_ADD(gtr, PLACE_LABEL_MTID, I6TargetCode::place_label);
    METHOD_ADD(gtr, EVALUATE_LABEL_MTID, I6TargetCode::evaluate_label);
    METHOD_ADD(gtr, INVOKE_PRIMITIVE_MTID, I6TargetCode::invoke_primitive);
    METHOD_ADD(gtr, INVOKE_FUNCTION_MTID, I6TargetCode::invoke_function);
    METHOD_ADD(gtr, INVOKE_OPCODE_MTID, I6TargetCode::invoke_opcode);
    METHOD_ADD(gtr, ASSEMBLY_MARKER_MTID, I6TargetCode::assembly_marker);
}

§2. Functions. Inform 6 originated as an assembler briefly called "zass", and its assembly-language character can still be seen in the way functions are declared:

[ FunctionName local1 local2 local3 ... localn;
    ...
];

Here local1, local2, ..., localn are all of the local variables accessible from the function; the earliest will be used as call parameters, all subsequent ones being initially zero.

void I6TargetCode::declare_function(code_generator *gtr, code_generation *gen,
    vanilla_function *vf) {
    segmentation_pos saved = CodeGen::select(gen, functions_I7CGS);
    if (vf == NULL) internal_error("no vg");
    text_stream *fn_name = vf->identifier;
    text_stream *OUT = CodeGen::current(gen);
    Open the function2.1;

    if (Str::eq(fn_name, I"Main"))                 Inject code at the top of Main2.3;
    if (Str::eq(fn_name, I"DebugAction"))          Inject code at the top of DebugAction2.4;
    if (Str::eq(fn_name, I"DebugAttribute"))       Inject code at the top of DebugAttribute2.5;
    if (Str::eq(fn_name, I"DebugProperty"))        Inject code at the top of DebugProperty2.6;
    if (Str::eq(fn_name, I"FINAL_CODE_STARTUP_R")) Inject code at the top of FINAL_CODE_STARTUP_R2.7;

    Vanilla::node(gen, vf->function_body);  This compiles the body of the function

    Close the function2.2;
    CodeGen::deselect(gen, saved);
}

§2.1. Open the function2.1 =

    WRITE("[ %S", fn_name);
    text_stream *var_name;
    LOOP_OVER_LINKED_LIST(var_name, text_stream, vf->locals)
        WRITE(" %S", var_name);
    WRITE(";\n"); INDENT;

This code is used in §2.

§2.2. Close the function2.2 =

    OUTDENT; WRITE("];\n");

This code is used in §2.

§2.3. A few functions will be sneakily rewritten in passing. This is done to handle specific features of the Z or Glulx virtual machines which do not meaningfully exist in any wider cross-platform way. Although this could all be done by having a slightly more elaborate linker and then including the code below in kits (as was indeed done during 2020), it's really better that the Inter tree not have to refer to eldritch Z-only symbols like #largest_object or Glulx-only symbols like #g$self.

Inject code at the top of Main2.3 =

    WRITE("#ifdef TARGET_ZCODE; max_z_object = #largest_object - 255; #endif;\n");

This code is used in §2.

§2.4. Inject code at the top of DebugAction2.4 =

    WRITE("#ifdef TARGET_GLULX;\n");
    WRITE("if (a < 4096) {\n");
    WRITE("    if (a < 0 || a >= #identifiers_table-->7) print \"<invalid action \", a, \">\";\n");
    WRITE("    else {\n");
    WRITE("        str = #identifiers_table-->6;\n");
    WRITE("        str = str-->a;\n");
    WRITE("        if (str) print (string) str; else print \"<unnamed action \", a, \">\";\n");
    WRITE("        return;\n");
    WRITE("    }\n");
    WRITE("}\n");
    WRITE("#endif;\n");
    WRITE("#ifdef TARGET_ZCODE;\n");
    WRITE("if (a < 4096) {\n");
    WRITE("    anames = #identifiers_table;\n");
    WRITE("    anames = anames + 2*(anames-->0) + 2*48;\n");
    WRITE("    print (string) anames-->a;\n");
    WRITE("    return;\n");
    WRITE("}\n");
    WRITE("#endif;\n");

This code is used in §2.

§2.5. Inject code at the top of DebugAttribute2.5 =

    I6_GEN_DATA(DebugAttribute_seen) = TRUE;
    WRITE("#ifdef TARGET_GLULX;\n");
    WRITE("if (a < 0 || a >= NUM_ATTR_BYTES*8) print \"<invalid attribute \", a, \">\";\n");
    WRITE("else {\n");
    WRITE("    str = #identifiers_table-->4;\n");
    WRITE("    str = str-->a;\n");
    WRITE("    if (str) print (string) str; else print \"<unnamed attribute \", a, \">\";\n");
    WRITE("}\n");
    WRITE("return;\n");
    WRITE("#endif;\n");
    WRITE("#ifdef TARGET_ZCODE;\n");
    WRITE("if (a < 0 || a >= 48) print \"<invalid attribute \", a, \">\";\n");
    WRITE("else {\n");
    WRITE("    anames = #identifiers_table; anames = anames + 2*(anames-->0);\n");
    WRITE("    print (string) anames-->a;\n");
    WRITE("}\n");
    WRITE("return;\n");
    WRITE("#endif;\n");

This code is used in §2.

§2.6. Inject code at the top of DebugProperty2.6 =

    WRITE("print (property) p;\n");
    WRITE("return;\n");

This code is used in §2.

§2.7. This enables a speed optimisation in the Glulx virtual machine which reimplements some of the veneer functions in "hardware". If it weren't here, or if the Gestalt said that the VM didn't support this after all, no harm would be done except for a slight slowdown.

Inject code at the top of FINAL_CODE_STARTUP_R2.7 =

    WRITE("#ifdef TARGET_GLULX;\n");
    WRITE("@gestalt 9 0 res;\n");
    WRITE("if (res == 0) rfalse;\n");
    WRITE("addr = #classes_table;\n");
    WRITE("@accelparam 0 addr;\n");
    WRITE("@accelparam 1 INDIV_PROP_START;\n");
    WRITE("@accelparam 2 Class;\n");
    WRITE("@accelparam 3 Object;\n");
    WRITE("@accelparam 4 Routine;\n");
    WRITE("@accelparam 5 String;\n");
    WRITE("addr = #globals_array + WORDSIZE * #g$self;\n");
    WRITE("@accelparam 6 addr;\n");
    WRITE("@accelparam 7 NUM_ATTR_BYTES;\n");
    WRITE("addr = #cpv__start;\n");
    WRITE("@accelparam 8 addr;\n");
    WRITE("@accelfunc 1 Z__Region;\n");
    WRITE("@accelfunc 2 CP__Tab;\n");
    WRITE("@accelfunc 3 RA__Pr;\n");
    WRITE("@accelfunc 4 RL__Pr;\n");
    WRITE("@accelfunc 5 OC__Cl;\n");
    WRITE("@accelfunc 6 RV__Pr;\n");
    WRITE("@accelfunc 7 OP__Pr;\n");
    WRITE("#endif;\n");
    WRITE("rfalse;\n");

This code is used in §2.

§3. Labels. Labels in Inform 6 are jump destinations, much as in C they are goto destinations. A full stop indicates where they are positioned:

    if (whatever) jump Catastrophe;
        ...
    .Catastrophe;
        ...

Inter identifiers for labels also start with full stops. So:

void I6TargetCode::place_label(code_generator *gtr, code_generation *gen,
    text_stream *label_name) {
    text_stream *OUT = CodeGen::current(gen);
    WRITE("%S;\n", label_name);
}
void I6TargetCode::evaluate_label(code_generator *gtr, code_generation *gen,
    text_stream *label_name) {
    text_stream *OUT = CodeGen::current(gen);
    LOOP_THROUGH_TEXT(pos, label_name)
        if (Str::get(pos) != '.')
            PUT(Str::get(pos));
}

§4. Function invocations. Or in other words, function calls. These are easy: the syntax is exactly what it would be for C.

void I6TargetCode::invoke_function(code_generator *gtr, code_generation *gen,
    inter_tree_node *P, vanilla_function *vf, int void_context) {
    text_stream *OUT = CodeGen::current(gen);
    WRITE("%S(", vf->identifier);
    int c = 0;
    LOOP_THROUGH_INTER_CHILDREN(F, P) {
        if (c++ > 0) WRITE(", ");
        Vanilla::node(gen, F);
    }
    WRITE(")");
    if (void_context) WRITE(";\n");
}

§5. Assembly language. In general, we make no attempt to police the supposedly valid assembly language given to us here. Glulx has one set, Z another. Any assembly language in the Inter tree results from kit material; and if the author of such a kit tries to use an invalid opcode, then the result won't compile under I6, but none of that is our business here.

The @aread opcode is a valid Z-machine opcode, but owing to the way I6 handles the irreconcilable change in syntax for the same opcode in V3 and V4-5 of the Z-machine specification, there is no good way to assemble it using @ notation unless we want to save the result. (See the Z-Machine Standards Document.) As a dodge, we use the Inform 6 statement read X Y instead.

void I6TargetCode::invoke_opcode(code_generator *gtr, code_generation *gen,
    text_stream *opcode, int operand_count, inter_tree_node **operands,
    inter_tree_node *label, int label_sense) {
    text_stream *OUT = CodeGen::current(gen);
    if (Str::eq(opcode, I"@aread")) WRITE("read");
    else WRITE("%S", opcode);
    for (int opc = 0; opc < operand_count; opc++) {
        WRITE(" ");
        Vanilla::node(gen, operands[opc]);
    }
    if (label) {
        WRITE(" ?");
        if (label_sense == FALSE) WRITE("~");
        Vanilla::node(gen, label);
    }
    WRITE(";\n");
}

void I6TargetCode::assembly_marker(code_generator *gtr, code_generation *gen, inter_ti marker) {
    text_stream *OUT = CodeGen::current(gen);
    switch (marker) {
        case ASM_ARROW_ASMMARKER: WRITE("->"); break;
        case ASM_SP_ASMMARKER: WRITE("sp"); break;
        case ASM_RTRUE_ASMMARKER: WRITE("?rtrue"); break;
        case ASM_RFALSE_ASMMARKER: WRITE("?rfalse"); break;
        case ASM_NEG_ASMMARKER: WRITE("~"); break;
        case ASM_NEG_RTRUE_ASMMARKER: WRITE("?~rtrue"); break;
        case ASM_NEG_RFALSE_ASMMARKER: WRITE("?~rfalse"); break;
        default:
            WRITE_TO(STDERR, "Unimplemented assembly marker is '%d'\n", marker);
            internal_error("unimplemented assembly marker");
    }
}

§6. Primitives.

void I6TargetCode::invoke_primitive(code_generator *gtr, code_generation *gen,
    inter_symbol *prim_name, inter_tree_node *P, int void_context) {
    inter_tree *I = gen->from;
    text_stream *OUT = CodeGen::current(gen);
    inter_ti bip = Primitives::to_BIP(I, prim_name);

    int suppress_terminal_semicolon = (void_context)?FALSE:TRUE;
    switch (bip) {
        Basic arithmetic and logical operations6.1;
        Storing or otherwise changing values6.2;
        VM stack access6.5;
        Control structures6.6;
        Indirect function calls6.7;
        Method calls6.8;
        Property value access6.3;
        Textual output6.9;
        The VM object tree6.10;
        default:
            WRITE_TO(STDERR, "Unimplemented primitive is '%S'\n",
                InterSymbol::identifier(prim_name));
            internal_error("unimplemented prim");
    }
    if (suppress_terminal_semicolon == FALSE) WRITE(";\n");
}

§6.1. Mostly easy, because the Inter primitives here were so closely modelled on their Inform 6 analogues in the first place.

For example, although !alternative is a very unusual linguistic feature — it allows alternatives in several conditions, e.g., if (x == 1 or 2 or 3) ... — it corresponds directly to the or keyword of Inform 6, so generating it is trivial.

Basic arithmetic and logical operations6.1 =

    case PLUS_BIP:          WRITE("("); VNODE_1C; WRITE(" + "); VNODE_2C; WRITE(")"); break;
    case MINUS_BIP:         WRITE("("); VNODE_1C; WRITE(" - "); VNODE_2C; WRITE(")"); break;
    case UNARYMINUS_BIP:    WRITE("(-("); VNODE_1C; WRITE("))"); break;
    case TIMES_BIP:         WRITE("("); VNODE_1C; WRITE("*"); VNODE_2C; WRITE(")"); break;
    case DIVIDE_BIP:        WRITE("("); VNODE_1C; WRITE("/"); VNODE_2C; WRITE(")"); break;
    case MODULO_BIP:        WRITE("("); VNODE_1C; WRITE("%%"); VNODE_2C; WRITE(")"); break;
    case BITWISEAND_BIP:    WRITE("(("); VNODE_1C; WRITE(")&("); VNODE_2C; WRITE("))"); break;
    case BITWISEOR_BIP:     WRITE("(("); VNODE_1C; WRITE(")|("); VNODE_2C; WRITE("))"); break;
    case BITWISENOT_BIP:    WRITE("(~("); VNODE_1C; WRITE("))"); break;
    case NOT_BIP:           WRITE("(~~("); VNODE_1C; WRITE("))"); break;
    case AND_BIP:           WRITE("(("); VNODE_1C; WRITE(") && ("); VNODE_2C; WRITE("))"); break;
    case OR_BIP:            WRITE("(("); VNODE_1C; WRITE(") || ("); VNODE_2C; WRITE("))"); break;
    case EQ_BIP:            WRITE("("); VNODE_1C; WRITE(" == "); VNODE_2C; WRITE(")"); break;
    case NE_BIP:            WRITE("("); VNODE_1C; WRITE(" ~= "); VNODE_2C; WRITE(")"); break;
    case GT_BIP:            WRITE("("); VNODE_1C; WRITE(" > "); VNODE_2C; WRITE(")"); break;
    case GE_BIP:            WRITE("("); VNODE_1C; WRITE(" >= "); VNODE_2C; WRITE(")"); break;
    case LT_BIP:            WRITE("("); VNODE_1C; WRITE(" < "); VNODE_2C; WRITE(")"); break;
    case LE_BIP:            WRITE("("); VNODE_1C; WRITE(" <= "); VNODE_2C; WRITE(")"); break;
    case OFCLASS_BIP:       WRITE("("); VNODE_1C; WRITE(" ofclass "); VNODE_2C; WRITE(")"); break;
    case IN_BIP:            WRITE("("); VNODE_1C; WRITE(" in "); VNODE_2C; WRITE(")"); break;
    case NOTIN_BIP:         WRITE("("); VNODE_1C; WRITE(" notin "); VNODE_2C; WRITE(")"); break;
    case LOOKUP_BIP:        WRITE("("); VNODE_1C; WRITE("-->("); VNODE_2C; WRITE("))"); break;
    case LOOKUPBYTE_BIP:    WRITE("("); VNODE_1C; WRITE("->("); VNODE_2C; WRITE("))"); break;
    case ALTERNATIVE_BIP:   VNODE_1C; WRITE(" or "); VNODE_2C; break;
    case SEQUENTIAL_BIP:    WRITE("("); VNODE_1C; WRITE(","); VNODE_2C; WRITE(")"); break;
    case TERNARYSEQUENTIAL_BIP: Generate primitive for ternarysequential6.1.1; break;
    case RANDOM_BIP:        WRITE("random("); VNODE_1C; WRITE(")"); break;

This code is used in §6.

§6.1.1. But the unfortunate !ternarysequential a b c needs some gymnastics. It would be trivial to generate to C with the serial comma operator: (a, b, c) evaluates a, then throws that away and evaluates b, then throws that away too and returns the value of c.

The same effect is annoyingly difficult to get out of the sometimes shaky I6 compiler's expression parser. I6 does support the comma operator, so at first sight (a, b, c) ought to work in I6, too. And it does, right up to the point where some of the token values themselves include invocations of functions. It is a known infelicity of the I6 syntax analyser that it won't always allow the serial comma to be mixed in the same expression with the function argument comma: for example in the case (a(b, c), d), where the first comma constructs a list of arguments and the second is the operator. (Many such expressions work fine in I6 — but not all.)

That being so, we use the following circumlocution:

    (c) + 0*((b) + (a))

Because I6 evaluates the leaves in an expression tree right-to-left, not left-to-right, the parameter assignments happen first, then the conditions, then the result.

Generate primitive for ternarysequential6.1.1 =

    WRITE("(\n"); INDENT;
    WRITE("! This evaluates last\n"); VNODE_3C;
    OUTDENT; WRITE("+\n"); INDENT;
    WRITE("0*(\n"); INDENT;
    WRITE("! This evaluates second\n");
    WRITE("((\n"); INDENT; VNODE_2C;
    OUTDENT; WRITE("\n))\n");
    OUTDENT; WRITE("+\n"); INDENT;
    WRITE("! This evaluate first\n");
    WRITE("("); VNODE_1C; WRITE(")");
    OUTDENT; WRITE(")\n");
    OUTDENT; WRITE(")\n");

This code is used in §6.1.

§6.2. These are the seven primitives which change a storage item given by a reference, which is always the first child of the primitive node. It might, for example, be a global variable, or a memory location.

Storing or otherwise changing values6.2 =

    case STORE_BIP:         Perform a store6.2.1; break;
    case PREINCREMENT_BIP:  Perform a store6.2.1; break;
    case POSTINCREMENT_BIP: Perform a store6.2.1; break;
    case PREDECREMENT_BIP:  Perform a store6.2.1; break;
    case POSTDECREMENT_BIP: Perform a store6.2.1; break;
    case SETBIT_BIP:        Perform a store6.2.1; break;
    case CLEARBIT_BIP:      Perform a store6.2.1; break;

This code is used in §6.

§6.2.1. Perform a store6.2.1 =

    inter_tree_node *storage_ref = InterTree::first_child(P);
    if (storage_ref->W.instruction[0] == REFERENCE_IST)
        storage_ref = InterTree::first_child(storage_ref);
    if ((ReferenceInstruction::node_is_ref_to(gen->from, InterTree::first_child(P),
        PROPERTYVALUE_BIP)) &&
        (I6TargetCode::pval_case(storage_ref) != I6G_CAN_PROVE_IS_OBJ_PROPERTY)) {
        Alter a property value6.2.1.2;
    } else {
        Alter some other storage6.2.1.1;
    }

This code is used in §6.2 (7 times).

§6.2.1.1. The easy case first: here, whatever the storage is (for example, a variable), it's one that we can simply treat as an lvalue in Inform 6 (for example, by giving its variable name). For example, the memory location A-->3 can be assigned to, or can have ++ or -- applied to it in I6.

Note that this case even includes some property values: if we can see that P is the explicit name of a property we are storing in a VM-property, then we can use O.P as an Inform 6 lvalue, and all is well, and we then end up with code such as ++(O.P).

Alter some other storage6.2.1.1 =

    switch (bip) {
        case PREINCREMENT_BIP:  WRITE("++("); VNODE_1C; WRITE(")"); break;
        case POSTINCREMENT_BIP: WRITE("("); VNODE_1C; WRITE(")++"); break;
        case PREDECREMENT_BIP:  WRITE("--("); VNODE_1C; WRITE(")"); break;
        case POSTDECREMENT_BIP: WRITE("("); VNODE_1C; WRITE(")--"); break;
        case STORE_BIP:         WRITE("("); VNODE_1C; WRITE(" = "); VNODE_2C; WRITE(")"); break;
        case SETBIT_BIP:        VNODE_1C; WRITE(" = "); VNODE_1C; WRITE(" | "); VNODE_2C; break;
        case CLEARBIT_BIP:      VNODE_1C; WRITE(" = "); VNODE_1C; WRITE(" &~ ("); VNODE_2C; WRITE(")"); break;
    }

This code is used in §6.2.1.

§6.2.1.2. But not all property values can be written as Inform 6 lvalues. If the I7 property P is being stored as a VM-attribute A, then there is no lvalue which expresses the value of A for an object O: instead one must use give O A to set it, give O ~A to unset it, and (O has A) to test it. And there will also be cases where P cannot be identified at compile-time, so that we have no way to know whether it will be stored as a VM-attribute or not.

To handle these two cases, then, we will compile an attempt to store or modify a property value either as a give statement — if we can prove P is being stored in a VM-attribute — or else as a function call to a general-purpose function called _final_change_property.

Alter a property value6.2.1.2 =

    inter_tree_node *VP = InterTree::second_child(P);
    int set = NOT_APPLICABLE;
    if (Inode::is(VP, VAL_IST)) {
        inter_pair val = ValInstruction::value(VP);
        if (InterValuePairs::is_number(val)) {
            if (InterValuePairs::is_zero(val)) set = FALSE;
            else if (InterValuePairs::is_one(val)) set = TRUE;
        }
    }

    int c = I6TargetCode::pval_case(storage_ref);
    if ((c == I6G_CAN_PROVE_IS_OBJ_ATTRIBUTE) && (bip == STORE_BIP) && (set == TRUE)) {
        WRITE("give "); Vanilla::node(gen, InterTree::second_child(storage_ref));
        WRITE(" %S", I6TargetCode::inner_name(gen, InterTree::third_child(storage_ref)));
    } else if ((c == I6G_CAN_PROVE_IS_OBJ_ATTRIBUTE) && (bip == STORE_BIP) && (set == FALSE)) {
        WRITE("give "); Vanilla::node(gen, InterTree::second_child(storage_ref));
        WRITE(" ~%S", I6TargetCode::inner_name(gen, InterTree::third_child(storage_ref)));
    } else {
        WRITE("(");
        switch (bip) {
            case STORE_BIP:         WRITE("_final_store_property"); break;
            case PREINCREMENT_BIP:  WRITE("_final_preinc_property"); break;
            case POSTINCREMENT_BIP: WRITE("_final_postinc_property"); break;
            case PREDECREMENT_BIP:  WRITE("_final_predec_property"); break;
            case POSTDECREMENT_BIP: WRITE("_final_postdec_property"); break;
            case SETBIT_BIP:        WRITE("_final_setbit_property"); break;
            case CLEARBIT_BIP:      WRITE("_final_clearbit_property"); break;
        }
        WRITE("(");
        Vanilla::node(gen, InterTree::first_child(storage_ref));
        WRITE(",");
        Vanilla::node(gen, InterTree::second_child(storage_ref));
        WRITE(",");
        Vanilla::node(gen, InterTree::third_child(storage_ref));
        switch (bip) {
            case STORE_BIP:         WRITE(", "); VNODE_2C; break;
            case SETBIT_BIP:        WRITE(", "); VNODE_2C; break;
            case CLEARBIT_BIP:      WRITE(", "); VNODE_2C; break;
        }
        WRITE("))");
    }

This code is used in §6.2.1.

§6.3. Reading property values is easier. The general case, similarly, is to call a function for this, but an important optimisation collapses this to the use of the has or . operators in I6 where we can prove at compile-time that the property in question is stored as a VM-attribute (resp., a VM-property) of what is definitely a VM-object. This optimisation results in faster code.

Property value access6.3 =

    case PROPERTYEXISTS_BIP:
        I6_GEN_DATA(value_ranges_needed) = TRUE;
        I6_GEN_DATA(value_property_holders_needed) = TRUE;
        WRITE("(_final_propertyexists("); VNODE_1C; WRITE(", "); VNODE_2C; WRITE(", ");
            VNODE_3C; WRITE("))"); break;
    case PROPERTYARRAY_BIP: WRITE("(_final_propertyarray("); VNODE_1C; WRITE(", ");
            VNODE_2C; WRITE(", "); VNODE_3C; WRITE("))"); break;
    case PROPERTYLENGTH_BIP: WRITE("(_final_propertylength("); VNODE_1C; WRITE(", ");
            VNODE_2C; WRITE(", "); VNODE_3C; WRITE("))"); break;
    case PROPERTYVALUE_BIP: {
        inter_tree_node *KP = InterTree::first_child(P);
        inter_tree_node *OP = InterTree::second_child(P);
        inter_tree_node *PP = InterTree::third_child(P);
        switch (I6TargetCode::pval_case(P)) {
            case I6G_CAN_PROVE_IS_OBJ_ATTRIBUTE:
                WRITE("("); VNODE_2C;
                WRITE(" has %S", I6TargetCode::inner_name(gen, PP)); WRITE(")"); break;
            case I6G_CAN_PROVE_IS_OBJ_PROPERTY:
                WRITE("("); VNODE_2C;
                WRITE(".%S", I6TargetCode::inner_name(gen, PP)); WRITE(")"); break;
            case I6G_CANNOT_PROVE:
                I6_GEN_DATA(value_property_holders_needed) = TRUE;
                I6TargetCode::eval_property_list(gen, KP, OP, PP, 0); break;
        }
        break;
    }

This code is used in §6.

§6.4. In the most general case of !propertyvalue, we will end up calling the function _final_propertyvalue. But we don't do so right away because, annoyingly, !propertyvalue can have !alternative children supplied. We might find this, for example:

inv !if
    inv !propertyvalue
        val K_object harmonium
        inv !alternative
            val K_value P_sonorous
            val K_value P_muted

...arising from kit code such as if (harmonium has sonorous or muted) .... This only seldom arises, so perhaps we can be given for handling it less than optimally in all cases. We turn it into:

    if (((or_tmp_var = harmonium) && (or_tmp_var has sonorous)) ||
        (or_tmp_var has muted))

Note that or_tmp_var is used here so that the left operand, i.e., the object, is evaluated only once — in case there are side-effects of the evaluation.

void I6TargetCode::eval_property_list(code_generation *gen, inter_tree_node *K,
    inter_tree_node *X, inter_tree_node *Y, int depth) {
    text_stream *OUT = CodeGen::current(gen);
    if (Inode::is(Y, INV_IST)) {
        if (InvInstruction::method(Y) == PRIMITIVE_INVMETH) {
            inter_symbol *prim = InvInstruction::primitive(Y);
            inter_ti ybip = Primitives::to_BIP(gen->from, prim);
            if (ybip == ALTERNATIVE_BIP) {
                if (depth == 0) { WRITE("((or_tmp_var = "); Vanilla::node(gen, X); WRITE(") && (("); }
                I6TargetCode::eval_property_list(gen, K, NULL, InterTree::first_child(Y), depth+1);
                WRITE(") || (");
                I6TargetCode::eval_property_list(gen, K, NULL, InterTree::second_child(Y), depth+1);
                if (depth == 0) { WRITE(")))"); }
                return;
            }
        }
    }
    switch (I6TargetCode::pval_case_inner(K, Y)) {
        case I6G_CAN_PROVE_IS_OBJ_ATTRIBUTE:
            WRITE("("); if (X) Vanilla::node(gen, X); else WRITE("or_tmp_var");
            WRITE(" has %S", I6TargetCode::inner_name(gen, Y)); WRITE(")"); break;
        case I6G_CAN_PROVE_IS_OBJ_PROPERTY:
            WRITE("("); if (X) Vanilla::node(gen, X); else WRITE("or_tmp_var");
            WRITE(".%S", I6TargetCode::inner_name(gen, Y)); WRITE(")"); break;
        case I6G_CANNOT_PROVE:
            WRITE("_final_propertyvalue(");
            Vanilla::node(gen, K);
            WRITE(", ");
            if (X) Vanilla::node(gen, X); else WRITE("or_tmp_var");
            WRITE(", ");
            Vanilla::node(gen, Y);
            WRITE(")"); break;
    }
}

§6.5. VM stack access6.5 =

    case PUSH_BIP:          WRITE("@push "); VNODE_1C; break;
    case PULL_BIP:          WRITE("@pull "); VNODE_1C; break;

This code is used in §6.

§6.6. Control structures6.6 =

    case BREAK_BIP:         WRITE("break"); break;
    case CONTINUE_BIP:      WRITE("continue"); break;
    case RETURN_BIP:        Generate primitive for return6.6.1; break;
    case JUMP_BIP:          WRITE("jump "); VNODE_1C; break;
    case QUIT_BIP:          WRITE("quit"); break;
    case RESTORE_BIP:       WRITE("restore "); VNODE_1C; break;
    case IF_BIP:            Generate primitive for if6.6.2; break;
    case IFDEBUG_BIP:       Generate primitive for ifdebug6.6.3; break;
    case IFSTRICT_BIP:      Generate primitive for ifstrict6.6.4; break;
    case IFELSE_BIP:        Generate primitive for ifelse6.6.5; break;
    case WHILE_BIP:         Generate primitive for while6.6.6; break;
    case DO_BIP:            Generate primitive for do6.6.7; break;
    case FOR_BIP:           Generate primitive for for6.6.8; break;
    case OBJECTLOOP_BIP:    Generate primitive for objectloop6.6.9; break;
    case OBJECTLOOPX_BIP:   Generate primitive for objectloopx6.6.10; break;
    case SWITCH_BIP:        Generate primitive for switch6.6.11; break;
    case CASE_BIP:          Generate primitive for case6.6.12; break;
    case ALTERNATIVECASE_BIP: VNODE_1C; WRITE(", "); VNODE_2C; break;
    case DEFAULT_BIP:       Generate primitive for default6.6.13; break;

This code is used in §6.

§6.6.1. Generate primitive for return6.6.1 =

    int rboolean = NOT_APPLICABLE;
    inter_tree_node *V = InterTree::first_child(P);
    if (Inode::is(V, VAL_IST)) {
        inter_pair val = ValInstruction::value(V);
        if (InterValuePairs::is_zero(val)) rboolean = FALSE;
        else if (InterValuePairs::is_one(val)) rboolean = TRUE;
    }
    switch (rboolean) {
        case FALSE: WRITE("rfalse"); break;
        case TRUE: WRITE("rtrue"); break;
        case NOT_APPLICABLE: WRITE("return "); Vanilla::node(gen, V); break;
    }

This code is used in §6.6.

§6.6.2. Generate primitive for if6.6.2 =

    WRITE("if ("); VNODE_1C; WRITE(") {\n"); INDENT; VNODE_2C;
    OUTDENT; WRITE("}\n");
    suppress_terminal_semicolon = TRUE;

This code is used in §6.6.

§6.6.3. Generate primitive for ifdebug6.6.3 =

    WRITE("#ifdef DEBUG;\n"); INDENT; VNODE_1C; OUTDENT; WRITE("#endif;\n");
    suppress_terminal_semicolon = TRUE;

This code is used in §6.6.

§6.6.4. Generate primitive for ifstrict6.6.4 =

    WRITE("#ifdef STRICT_MODE;\n"); INDENT; VNODE_1C; OUTDENT; WRITE("#endif;\n");
    suppress_terminal_semicolon = TRUE;

This code is used in §6.6.

§6.6.5. Generate primitive for ifelse6.6.5 =

    WRITE("if ("); VNODE_1C; WRITE(") {\n"); INDENT; VNODE_2C; OUTDENT;
    WRITE("} else {\n"); INDENT; VNODE_3C; OUTDENT; WRITE("}\n");
    suppress_terminal_semicolon = TRUE;

This code is used in §6.6.

§6.6.6. Generate primitive for while6.6.6 =

    WRITE("while ("); VNODE_1C; WRITE(") {\n"); INDENT; VNODE_2C; OUTDENT; WRITE("}\n");
    suppress_terminal_semicolon = TRUE;

This code is used in §6.6.

§6.6.7. Generate primitive for do6.6.7 =

    WRITE("do {"); VNODE_2C; WRITE("} until (\n"); INDENT; VNODE_1C; OUTDENT; WRITE(")\n");

This code is used in §6.6.

§6.6.8. Generate primitive for for6.6.8 =

    WRITE("for (");
    inter_tree_node *INIT = InterTree::first_child(P);
    if (!((Inode::is(INIT, VAL_IST)) &&
        (InterValuePairs::is_number(ValInstruction::value(INIT))) &&
        (InterValuePairs::to_number(ValInstruction::value(INIT)) == 1)))
            VNODE_1C;
    WRITE(":"); VNODE_2C;
    WRITE(":");
    inter_tree_node *U = InterTree::third_child(P);
    if (Inode::isnt(U, VAL_IST))
    Vanilla::node(gen, U);
    WRITE(") {\n"); INDENT; VNODE_4C;
    OUTDENT; WRITE("}\n");
    suppress_terminal_semicolon = TRUE;

This code is used in §6.6.

§6.6.9. Generate primitive for objectloop6.6.9 =

    int in_flag = FALSE;
    inter_tree_node *U = InterTree::third_child(P);
    if ((Inode::is(U, INV_IST)) &&
        (InvInstruction::method(U) == PRIMITIVE_INVMETH)) {
        inter_symbol *prim = InvInstruction::primitive(U);
        if ((prim) && (Primitives::to_BIP(I, prim) == IN_BIP)) in_flag = TRUE;
    }

    WRITE("objectloop ");
    if (in_flag == FALSE) {
        WRITE("("); VNODE_1C; WRITE(" ofclass "); VNODE_2C;
        WRITE(" && ");
    } VNODE_3C;
    if (in_flag == FALSE) {
        WRITE(")");
    }
    WRITE(" {\n"); INDENT; VNODE_4C;
    OUTDENT; WRITE("}\n");
    suppress_terminal_semicolon = TRUE;

This code is used in §6.6.

§6.6.10. Generate primitive for objectloopx6.6.10 =

    WRITE("objectloop ("); VNODE_1C; WRITE(" ofclass "); VNODE_2C;
    WRITE(") {\n"); INDENT; VNODE_3C; OUTDENT; WRITE("}\n");
    suppress_terminal_semicolon = TRUE;

This code is used in §6.6.

§6.6.11. Generate primitive for switch6.6.11 =

    WRITE("switch ("); VNODE_1C;
    WRITE(") {\n"); INDENT; VNODE_2C; OUTDENT; WRITE("}\n");
    suppress_terminal_semicolon = TRUE;

This code is used in §6.6.

§6.6.12. Generate primitive for case6.6.12 =

    VNODE_1C; WRITE(":\n"); INDENT; VNODE_2C; WRITE(";\n"); OUTDENT;
    suppress_terminal_semicolon = TRUE;

This code is used in §6.6.

§6.6.13. Generate primitive for default6.6.13 =

    WRITE("default:\n"); INDENT; VNODE_1C; WRITE(";\n"); OUTDENT;
    suppress_terminal_semicolon = TRUE;

This code is used in §6.6.

§6.7. In Inform 6, as in C, a function which returns a value can be called in a void context (in which case its return value is thrown away); the syntax for calling a void function is identical to that for calling a value-returning function, so we can treat INDIRECT0V_BIP as the same as INDIRECT0_BIP, and so on.

Indirect function calls6.7 =

    case INDIRECT0_BIP: case INDIRECT0V_BIP:
        WRITE("("); VNODE_1C; WRITE(")()"); break;
    case INDIRECT1_BIP: case INDIRECT1V_BIP:
        WRITE("("); VNODE_1C; WRITE(")("); VNODE_2C; WRITE(")"); break;
    case INDIRECT2_BIP: case INDIRECT2V_BIP:
        WRITE("("); VNODE_1C; WRITE(")("); VNODE_2C; WRITE(","); VNODE_3C; WRITE(")");
        break;
    case INDIRECT3_BIP: case INDIRECT3V_BIP:
        WRITE("("); VNODE_1C; WRITE(")("); VNODE_2C; WRITE(","); VNODE_3C; WRITE(",");
        VNODE_4C; WRITE(")"); break;
    case INDIRECT4_BIP: case INDIRECT4V_BIP:
        WRITE("("); VNODE_1C; WRITE(")("); VNODE_2C; WRITE(","); VNODE_3C; WRITE(",");
        VNODE_4C; WRITE(","); VNODE_5C; WRITE(")"); break;
    case INDIRECT5_BIP: case INDIRECT5V_BIP:
        WRITE("("); VNODE_1C; WRITE(")("); VNODE_2C; WRITE(","); VNODE_3C; WRITE(",");
        VNODE_4C; WRITE(","); VNODE_5C; WRITE(","); VNODE_6C; WRITE(")"); break;
    case EXTERNALCALL_BIP:  internal_error("external calls impossible in Inform 6"); break;

This code is used in §6.

§6.8. Message calls are handled with functions (see below) in case the user is trying to send a message to a property stored in an attribute, or something like that.

Method calls6.8 =

    case MESSAGE0_BIP:      WRITE("_final_message0("); VNODE_1C; WRITE(", "); VNODE_2C; WRITE(")"); break;
    case MESSAGE1_BIP:      WRITE("_final_message1("); VNODE_1C; WRITE(", "); VNODE_2C; WRITE(", ");
                            VNODE_3C; WRITE(")"); break;
    case MESSAGE2_BIP:      WRITE("_final_message2("); VNODE_1C; WRITE(", "); VNODE_2C; WRITE(", ");
                            VNODE_3C; WRITE(","); VNODE_4C; WRITE(")"); break;
    case MESSAGE3_BIP:      WRITE("_final_message3("); VNODE_1C; WRITE(", "); VNODE_2C; WRITE(", ");
                            VNODE_3C; WRITE(","); VNODE_4C; WRITE(","); VNODE_5C; WRITE(")"); break;

This code is used in §6.

§6.9. Note that the only styles permitted are those from the original Z-machine, which is about the level of technology of a 1970s teletype. The !style number must be a constant 1, 2 or 3, or else plain roman is all you get.

Textual output6.9 =

    case PRINT_BIP:         WRITE("print "); CodeGen::lt_mode(gen, PRINTING_LTM);
                            VNODE_1C; CodeGen::lt_mode(gen, REGULAR_LTM); break;
    case PRINTCHAR_BIP:     WRITE("print (char) "); VNODE_1C; break;
    case PRINTNL_BIP:       WRITE("new_line"); break;
    case PRINTOBJ_BIP:      WRITE("print (object) "); VNODE_1C; break;
    case PRINTNUMBER_BIP:   WRITE("print "); VNODE_1C; break;
    case PRINTDWORD_BIP:    WRITE("print (address) "); VNODE_1C; break;
    case PRINTSTRING_BIP:   WRITE("print (string) "); VNODE_1C; break;
    case BOX_BIP:           WRITE("box "); CodeGen::lt_mode(gen, BOX_LTM);
                            VNODE_1C; CodeGen::lt_mode(gen, REGULAR_LTM); break;
    case SPACES_BIP:        WRITE("spaces "); VNODE_1C; break;
    case FONT_BIP:
        WRITE("if ("); VNODE_1C; WRITE(") { font on; } else { font off; }");
        suppress_terminal_semicolon = TRUE;
        break;
    case STYLE_BIP: {
        inter_tree_node *N = InterTree::first_child(P);
        inter_pair pair = ValInstruction::value(N);
        inter_ti style = InterValuePairs::to_number(pair);
        switch (style) {
            case 1: WRITE("style bold"); break;
            case 2: WRITE("style underline"); break;
            case 3: WRITE("style reverse"); break;
            default: WRITE("style roman");
        }
        break;
    }
    case ENABLEPRINTING_BIP:
        WRITE("#ifdef TARGET_GLULX;\n");
        WRITE("@setiosys 2 0; ! Set to use Glk\n");
        WRITE("@push 201;     ! = GG_MAINWIN_ROCK;\n");
        WRITE("@push 3;       ! = wintype_TextBuffer\n");
        WRITE("@push 0;\n");
        WRITE("@push 0;\n");
        WRITE("@push 0;\n");
        WRITE("@glk 35 5 sp;  ! glk_window_open, pushing a window ID\n");
        WRITE("@glk 47 1 0;   ! glk_set_window to that window ID\n");
        WRITE("#endif;\n");
        break;

This code is used in §6.

§6.10. The VM object tree6.10 =

    case MOVE_BIP:          WRITE("move "); VNODE_1C; WRITE(" to "); VNODE_2C; break;
    case REMOVE_BIP:        WRITE("remove "); VNODE_1C; break;
    case CHILD_BIP:         WRITE("child("); VNODE_1C; WRITE(")"); break;
    case CHILDREN_BIP:      WRITE("children("); VNODE_1C; WRITE(")"); break;
    case PARENT_BIP:        WRITE("parent("); VNODE_1C; WRITE(")"); break;
    case SIBLING_BIP:       WRITE("sibling("); VNODE_1C; WRITE(")"); break;
    case METACLASS_BIP:     WRITE("metaclass("); VNODE_1C; WRITE(")"); break;

This code is used in §6.

§7. Support code for property accesses. In the following, prop_node is a VAL_IST identifying the property being accessed: we return the "inner name" as text, if we can find one. This will only happen if the node evaluates to a named symbol which is the name of a property. See Vanilla Objects for more on inner names.

text_stream *I6TargetCode::inner_name(code_generation *gen, inter_tree_node *prop_node) {
    inter_symbol *prop_symbol = NULL;
    if (Inode::is(prop_node, VAL_IST)) {
        inter_pair val = ValInstruction::value(prop_node);
        if (InterValuePairs::is_symbolic(val))
            prop_symbol = InterValuePairs::to_symbol_at(val, prop_node);
    }
    if ((prop_symbol) && (InterSymbol::get_flag(prop_symbol, ATTRIBUTE_MARK_ISYMF))) {
        return VanillaObjects::inner_property_name(gen, prop_symbol);
    } else if ((prop_symbol) && (Inode::is(prop_symbol->definition, PROPERTY_IST))) {
        return VanillaObjects::inner_property_name(gen, prop_symbol);
    } else {
        return NULL;
    }
}

§8. I6TargetCode::pval_case applies to a !propertyvalue invocation node. That has three children: the kind, the object/owner, and the property itself. We look at the node and try to see if it's one of the two easy cases which enable more efficient code to be compiled (see above): in fact, it almost always is.

● We return I6G_CAN_PROVE_IS_OBJ_ATTRIBUTE if the kind is definitely OBJECT_TY and the property is stored in a VM-attribute;
● Or I6G_CAN_PROVE_IS_OBJ_PROPERTY if the kind is definitely OBJECT_TY and the property is stored in a VM-property;
● Or I6G_CANNOT_PROVE if we don't know.

define I6G_CAN_PROVE_IS_OBJ_ATTRIBUTE 1
define I6G_CAN_PROVE_IS_OBJ_PROPERTY 2
define I6G_CANNOT_PROVE 3

int I6TargetCode::pval_case(inter_tree_node *P) {
    while (Inode::is(P, REFERENCE_IST)) P = InterTree::first_child(P);
    inter_tree_node *prop_node = InterTree::third_child(P);
    return I6TargetCode::pval_case_inner(InterTree::first_child(P), prop_node);
}

int I6TargetCode::pval_case_inner(inter_tree_node *kind_node, inter_tree_node *prop_node) {
    inter_symbol *kind_symbol = NULL;
    if (Inode::is(kind_node, VAL_IST)) {
        inter_pair val = ValInstruction::value(kind_node);
        if (InterValuePairs::is_symbolic(val))
            kind_symbol = InterValuePairs::to_symbol_at(val, kind_node);
    }
    if (Str::eq(InterSymbol::trans(kind_symbol), I"OBJECT_TY") == FALSE)
        return I6G_CANNOT_PROVE;

    inter_symbol *prop_symbol = NULL;
    if (Inode::is(prop_node, VAL_IST)) {
        inter_pair val = ValInstruction::value(prop_node);
        if (InterValuePairs::is_symbolic(val))
            prop_symbol = InterValuePairs::to_symbol_at(val, prop_node);
    }
    if ((prop_symbol) && (InterSymbol::get_flag(prop_symbol, ATTRIBUTE_MARK_ISYMF))) {
        return I6G_CAN_PROVE_IS_OBJ_ATTRIBUTE;
    } else if ((prop_symbol) && (Inode::is(prop_symbol->definition, PROPERTY_IST))) {
        return I6G_CAN_PROVE_IS_OBJ_PROPERTY;
    } else {
        return I6G_CANNOT_PROVE;
    }
}

§9. The final functions. The generator above compiled calls to a handful of functions with names in the form _final_*; so these functions must clearly be supplied. It might seem that they ought to be included in, say, BasicInformKit and not here. But:

(1) They are needed only for Inform 6 usage, whereas BasicInformKit contains material used whatever the final code-generator;
(2) They are written in genuine Inform 6 code, not kit code, which looks like I6 and is very similar to it but is not quite the same. In kit code, O.P means "the value of the property P for the object O", but where P is the metadata array for the property. In genuine Inform 6, O.P expects P to be the actual VM-property. The following functions need the latter interpretation in order to work.

void I6TargetCode::end_generation(code_generator *gtr, code_generation *gen) {
    segmentation_pos saved = CodeGen::select(gen, functions_I7CGS);
    text_stream *OUT = CodeGen::current(gen);
    Most general implementation of !propertyvalue9.1;
    Most general implementation of !propertyexists9.2;
    Most general implementation of !propertyarray9.3;
    Most general implementation of !propertylength9.4;
    Most general implementation of writing to a property9.5;
    Implementation of !messageX9.6;
    CodeGen::deselect(gen, saved);
}

§9.1. See Inform 6 Objects for the runtime contents of the array of property metadata p. The following is more or less a safe general-purpose wrapper for the Inform 6 operator ., used as an rvalue, in cases where we cannot prove it would be safe to use . directly:

Most general implementation of !propertyvalue9.1 =

    WRITE("#ifdef BASICINFORMKIT;\n");
    WRITE("[ _final_propertyvalue K o p t;\n");
    WRITE("    if (K == OBJECT_TY) {\n");
    WRITE("        if (metaclass(o) == Object) {\n");
    WRITE("            t = p-->0; p = p-->1;\n");
    WRITE("            if (t == 2) { if (o has p) rtrue; rfalse; }\n");
    WRITE("            if (o provides p) return o.p;\n");
    WRITE("        }\n");
    WRITE("        rfalse;\n");
    WRITE("    } else {\n");
    WRITE("        t = value_property_holders-->K;\n");
    WRITE("        return (t.(p-->1))-->(o+COL_HSIZE);\n");
    WRITE("    }\n");
    WRITE("];\n");
    WRITE("#endif;\n");

This code is used in §9.

§9.2. Similarly, this is a safe wrapper for provides:

Most general implementation of !propertyexists9.2 =

    WRITE("#ifdef BASICINFORMKIT;\n");
    WRITE("[ _final_propertyexists K o p holder;\n");
    WRITE("if (K == OBJECT_TY) {\n");
    WRITE("    if ((o) && (metaclass(o) == Object)) {\n");
    WRITE("        if ((p-->0 == 2) || (o provides p-->1)) {\n");
    WRITE("            rtrue;\n");
    WRITE("        } else {\n");
    WRITE("            rfalse;\n");
    WRITE("        }\n");
    WRITE("    } else {\n");
    WRITE("        rfalse;\n");
    WRITE("    }\n");
    WRITE("} else {\n");
    WRITE("    if ((o >= 1) && (o <= value_ranges-->K)) {\n");
    WRITE("        holder = value_property_holders-->K;\n");
    WRITE("        if ((holder) && (holder provides p-->1)) {\n");
    WRITE("            rtrue;\n");
    WRITE("        } else {\n");
    WRITE("            rfalse;\n");
    WRITE("        }\n");
    WRITE("    } else {\n");
    WRITE("        rfalse;\n");
    WRITE("    }\n");
    WRITE("}\n");
    WRITE("rfalse; ];\n");
    WRITE("#endif;\n");

This code is used in §9.

§9.3. And this for .&. Note that we always return 0 if the owner is not an object.

Most general implementation of !propertyarray9.3 =

    WRITE("#ifdef BASICINFORMKIT;\n");
    WRITE("[ _final_propertyarray K o p v t;\n");
    WRITE("    if (K ~= OBJECT_TY) return 0;\n");
    WRITE("    t = p-->0; p = p-->1;\n");
    WRITE("    if (t == 2) return 0;\n");
    WRITE("    return o.&p;\n");
    WRITE("];\n");
    WRITE("#endif;\n");

This code is used in §9.

§9.4. And this for .#. Again, we always return 0 if the owner is not an object.

Most general implementation of !propertylength9.4 =

    WRITE("#ifdef BASICINFORMKIT;\n");
    WRITE("[ _final_propertylength K o p v t;\n");
    WRITE("    if (K ~= OBJECT_TY) return 0;\n");
    WRITE("    t = p-->0; p = p-->1;\n");
    WRITE("    if (t == 2) return 0;\n");
    WRITE("    return o.#p;\n");
    WRITE("];\n");
    WRITE("#endif;\n");

This code is used in §9.

§9.5. And this is a safe way to write to or otherwise alter O.P, laboriously written out as seven functions. (Speed is more important than conciseness here.)

Most general implementation of writing to a property9.5 =

    WRITE("#ifdef BASICINFORMKIT;\n");
    WRITE("[ _final_store_property K o p v t;\n");
    WRITE("    if (K == OBJECT_TY) {\n");
    WRITE("        if (metaclass(o) == Object) {\n");
    WRITE("            t = p-->0; p = p-->1;\n");
    WRITE("            if (t == 2) {\n");
    WRITE("                if (v) give o p; else give o ~p;\n");
    WRITE("            } else if (o provides p) {\n");
    WRITE("                o.p = v;\n");
    WRITE("            }\n");
    WRITE("        }\n");
    WRITE("    } else {\n");
    WRITE("        ((value_property_holders-->K).(p-->1))-->(o+COL_HSIZE) = v;\n");
    WRITE("    }\n");
    WRITE("];\n");
    WRITE("[ _final_preinc_property K o p t;\n");
    WRITE("    if (K == OBJECT_TY) {\n");
    WRITE("        if (metaclass(o) == Object) {\n");
    WRITE("            t = p-->0; p = p-->1;\n");
    WRITE("            if (t == 2) {\n");
    WRITE("                if (o has p) { give o ~p; rfalse; } give o p; rtrue;\n");
    WRITE("            } else if (o provides p) {\n");
    WRITE("                return ++(o.p);\n");
    WRITE("            }\n");
    WRITE("        }\n");
    WRITE("    } else {\n");
    WRITE("       return ++(((value_property_holders-->K).(p-->1))-->(o+COL_HSIZE));\n");
    WRITE("    }\n");
    WRITE("    return 0;\n");
    WRITE("];\n");
    WRITE("[ _final_predec_property K o p t;\n");
    WRITE("    if (K == OBJECT_TY) {\n");
    WRITE("        if (metaclass(o) == Object) {\n");
    WRITE("            t = p-->0; p = p-->1;\n");
    WRITE("            if (t == 2) {\n");
    WRITE("                if (o has p) { give o ~p; rfalse; } give o p; rtrue;\n");
    WRITE("            } else if (o provides p) {\n");
    WRITE("                return --(o.p);\n");
    WRITE("            }\n");
    WRITE("        }\n");
    WRITE("    } else {\n");
    WRITE("       return --(((value_property_holders-->K).(p-->1))-->(o+COL_HSIZE));\n");
    WRITE("    }\n");
    WRITE("    return 0;\n");
    WRITE("];\n");
    WRITE("[ _final_postinc_property K o p t;\n");
    WRITE("    if (K == OBJECT_TY) {\n");
    WRITE("        if (metaclass(o) == Object) {\n");
    WRITE("            t = p-->0; p = p-->1;\n");
    WRITE("            if (t == 2) {\n");
    WRITE("                if (o has p) { give o ~p; rtrue; } give o p; rfalse;\n");
    WRITE("            } else if (o provides p) {\n");
    WRITE("                return (o.p)++;\n");
    WRITE("            }\n");
    WRITE("        }\n");
    WRITE("    } else {\n");
    WRITE("       return (((value_property_holders-->K).(p-->1))-->(o+COL_HSIZE))++;\n");
    WRITE("    }\n");
    WRITE("    return 0;\n");
    WRITE("];\n");
    WRITE("[ _final_postdec_property K o p t;\n");
    WRITE("    if (K == OBJECT_TY) {\n");
    WRITE("        if (metaclass(o) == Object) {\n");
    WRITE("            t = p-->0; p = p-->1;\n");
    WRITE("            if (t == 2) {\n");
    WRITE("                if (o has p) { give o ~p; rtrue; } give o p; rfalse;\n");
    WRITE("            } else if (o provides p) {\n");
    WRITE("                return (o.p)--;\n");
    WRITE("            }\n");
    WRITE("        }\n");
    WRITE("    } else {\n");
    WRITE("       return (((value_property_holders-->K).(p-->1))-->(o+COL_HSIZE))--;\n");
    WRITE("    }\n");
    WRITE("    return 0;\n");
    WRITE("];\n");
    WRITE("[ _final_setbit_property K o p v t;\n");
    WRITE("    if (K == OBJECT_TY) {\n");
    WRITE("        if (metaclass(o) == Object) {\n");
    WRITE("            t = p-->0; p = p-->1;\n");
    WRITE("            if (t == 2) {\n");
    WRITE("                if (v & 1) give o p;\n");
    WRITE("            } else if (o provides p) {\n");
    WRITE("                o.p = o.p | v;\n");
    WRITE("            }\n");
    WRITE("        }\n");
    WRITE("    } else {\n");
    WRITE("        ((value_property_holders-->K).(p-->1))-->(o+COL_HSIZE) =\n");
    WRITE("            ((value_property_holders-->K).(p-->1))-->(o+COL_HSIZE) | v;\n");
    WRITE("    }\n");
    WRITE("];\n");
    WRITE("[ _final_clearbit_property K o p v t;\n");
    WRITE("    if (K == OBJECT_TY) {\n");
    WRITE("        if (metaclass(o) == Object) {\n");
    WRITE("            t = p-->0; p = p-->1;\n");
    WRITE("            if (t == 2) {\n");
    WRITE("                if (v & 1) give o ~p;\n");
    WRITE("            } else if (o provides p) {\n");
    WRITE("                o.p = o.p & ~v;\n");
    WRITE("            }\n");
    WRITE("        }\n");
    WRITE("    } else {\n");
    WRITE("        ((value_property_holders-->K).(p-->1))-->(o+COL_HSIZE) =\n");
    WRITE("            ((value_property_holders-->K).(p-->1))-->(o+COL_HSIZE) & ~v;\n");
    WRITE("    }\n");
    WRITE("];\n");
    WRITE("#endif;\n");

This code is used in §9.

§9.6. It's not entirely clear what the result of trying to send a message to an either/or property ought to be: nobody should ever do that. We're going to say that it's 0 here.

Implementation of !messageX9.6 =

    WRITE("#ifdef BASICINFORMKIT;\n");
    WRITE("[ _final_message0 o p q x a rv;\n");
    WRITE("    if (p-->0 == 2) return 0;\n");
    WRITE("    q = p-->1; return o.q();\n");
    WRITE("];\n");
    WRITE("[ _final_message1 o p v1 q x a rv;\n");
    WRITE("    if (p-->0 == 2) return 0;\n");
    WRITE("    q = p-->1; return o.q(v1);\n");
    WRITE("];\n");
    WRITE("[ _final_message2 o p v1 v2 q x a rv;\n");
    WRITE("    if (p-->0 == 2) return 0;\n");
    WRITE("    q = p-->1; return o.q(v1, v2);\n");
    WRITE("];\n");
    WRITE("[ _final_message3 o p v1 v2 v3 q x a rv;\n");
    WRITE("    if (p-->0 == 2) return 0;\n");
    WRITE("    q = p-->1; return o.q(v1, v2, v3);\n");
    WRITE("];\n");
    WRITE("#endif;\n");

This code is used in §9.