Emitting Inter Schemas

To compile Inter code following the model in an Inter schema tree.

§1. This section presents just one function to the rest of Inform: it compiles Inter code from a schema. Though there are many arguments, this is still fairly simple to use:

● I is the tree to compile code into. Code will appear at the current write position in that tree.
● VH is a value holster (see Value Holsters), but a simple one: it either says "generate code in a void context" (that's INTER_VOID_VHMODE) or "generate code in a value context" (INTER_VAL_VHMODE). The difference is that, say, statements such as print "Hello"; cannot be compiled in a value context, only in a void one.
● sch is the schema to compile from. It is unchanged by the process, except that nodes made inaccessible by conditional compilation are marked as such.
● If the schema mentions identifiers — as for example DoSomething(1, 2) mentions the identifier DoSomething — then these must somehow be matched up with inter_symbols giving them a meaning. finder says how: see Identifier Finders.
● As we have seen, schema notation is (almost) Inform 6 syntax, except for two big extensions: one is Inform 7 source text placed between (+ and +) markers, and the other is braced commands like {-by-reference: X}. The code below cannot deal with either of these. Instead, we must supply callback functions to deal with them as they arise. (Supplying NULL as either of these makes the relevant notation do nothing.)
● opaque_state is a pointer to any data which you, the caller, want to be passed through to those two callback functions. The code below otherwise makes no use of it; and it can of course be NULL if no state is needed.

So the simplest valid usage of the function would be something like:

    value_holster VH = Holsters::new(INTER_VOID_VHMODE);
    identifier_finder finder = IdentifierFinders::common_names_only();
    EmitInterSchemas::emit(I, &VH, sch, finder, NULL, NULL, NULL);

which roughly means "compile pure Inform 6 code to Inter in a void context, but do not recognise any identifiers as corresponding to local variables".

Note that emission can turn up syntax errors which went undetected earlier (because they depend more on context); if so, these are attached to the schema. It's the caller's responsibility to check for those and act accordingly.

void EmitInterSchemas::emit(inter_tree *I, value_holster *VH, inter_schema *sch,
    identifier_finder finder,
    void (*inline_command_handler)(value_holster *VH, inter_schema_token *t,
        void *opaque_state, int prim_cat, text_stream *L),
    void (*i7_source_handler)(value_holster *VH, text_stream *S,
        void *opaque_state, int prim_cat),
    void *opaque_state) {

    Reset the write position if we're in the middle of a switch statement1.1;
    Recursively deal with conditional compilation1.2;
    Traverse the tree, compiling each node1.3;
}

§1.1. This allows a very edgy edge case: schemas which make case constructions making sense only within a switch statement, but where the schema does not itself include the switch head or tail.

Reset the write position if we're in the middle of a switch statement1.1 =

    if (sch->mid_case) Produce::set_level_to_current_code_block_plus(I, 4);

This code is used in §1.

§1.2. The following looks for conditional compilations such as:

    #ifdef TARGET_GLULX;
    print "This is Glulx;
    #endif

and strikes out any nodes which are not to be compiled from — for example, the print statement here would be marked as blocked_by_conditional if the symbol TARGET_GLULX were not defined.

Note that this is done only once for each schema, so we are implicitly assuming that the outcome of #ifdef TARGET_GLULX; would be the same every time during the same run of inform7 or inter. But of course it must be, since although we may generate many times from the same schema, it will always be within the same machine architecture each time.

Recursively deal with conditional compilation1.2 =

    int again = TRUE;
    while (again) {
        again = FALSE;
        for (inter_schema_node *node = sch->node_tree; node; node=node->next_node)
            if (EmitInterSchemas::process_conditionals(I, node, finder))
                again = TRUE;
    }

This code is used in §1.

§2.

int EmitInterSchemas::process_conditionals(inter_tree *I, inter_schema_node *dir_node,
    identifier_finder finder) {
    if (dir_node == NULL) return FALSE;
    if (dir_node->blocked_by_conditional) return FALSE;
    if (dir_node->isn_type == DIRECTIVE_ISNT) Directive2.1;
    for (dir_node=dir_node->child_node; dir_node; dir_node=dir_node->next_node)
        if (EmitInterSchemas::process_conditionals(I, dir_node, finder))
            return TRUE;
    return FALSE;  signalling the function should not be called again
}

§2.1. Directive2.1 =

    if ((dir_node->dir_clarifier == IFDEF_I6RW) ||
        (dir_node->dir_clarifier == IFNDEF_I6RW) ||
        (dir_node->dir_clarifier == IFTRUE_I6RW) ||
        (dir_node->dir_clarifier == IFFALSE_I6RW)) {
        LOGIF(SCHEMA_COMPILATION, "Conditional directive in schema!\n");
        inter_schema_node *ifnot_node = NULL, *endif_node = NULL;
        Find the clauses of the conditional we will resolve2.1.1;

        text_stream *symbol_to_check = NULL;
        text_stream *value_to_check = NULL;
        inter_ti operation_to_check = 0;
        Work out what the condition is2.1.2;

        int val = -1, def = FALSE;
        Find out whether this symbol is defined, and if so, what its value is2.1.3;

        int decision = TRUE;
        Decide whether the condition is met or not2.1.4;

        Mark the three clause nodes as blocked2.1.5;

        if (decision == FALSE) Mark the if body as blocked2.1.6
        else Mark the if-not body as blocked2.1.7;

        if (Log::aspect_switched_on(SCHEMA_COMPILATION_DA)) {
            LOG("--- Resulting in: ---\n");
            for (inter_schema_node *at = dir_node; at; at = at->next_node)
                InterSchemas::log_just(at, 0);
            LOG("------\n");
        }
        return TRUE;  forcing this function to be called again
    }

This code is used in §2.

§2.1.1. The aim here is to find an innermost conditional, setting dir_node to its head, ifnot_node to the position of the #Ifnot — if there is one; they are optional in I6 — and endif_node to the position of its #Endif, whose existence is mandatory. For example:

    #ifdef TARGET_ZCODE;
    #ifdef DEBUG;            <--- dir_node
    print "ZD;
    #ifnot;                  <--- ifnot_node
    print "Z;
    #endif;                  <--- endif_node
    #endif;

Note that we only need find one such conditional, because once we resolve it, we will return but the function will then be applied again, and so on until all conditionals are resolved.

Find the clauses of the conditional we will resolve2.1.1 =

    inter_schema_node *at = dir_node->next_node;
    while (at) {
        if (at->blocked_by_conditional == FALSE) {
            if (at->dir_clarifier == IFDEF_I6RW)   { dir_node = at; ifnot_node = NULL; }
            if (at->dir_clarifier == IFNDEF_I6RW)  { dir_node = at; ifnot_node = NULL; }
            if (at->dir_clarifier == IFTRUE_I6RW)  { dir_node = at; ifnot_node = NULL; }
            if (at->dir_clarifier == IFFALSE_I6RW) { dir_node = at; ifnot_node = NULL; }
            if (at->dir_clarifier == IFNOT_I6RW)   { ifnot_node = at; }
            if (at->dir_clarifier == ENDIF_I6RW)   { endif_node = at; break; }
        }
        at = at->next_node;
    }
    if (endif_node == NULL) {
        I6Errors::issue_at_node(dir_node, I"no matching '#endif'");
        return FALSE;
    }

This code is used in §2.1.

§2.1.2. We are going to recognise only very simple conditions, such as:

    #ifdef SYMBOL;
    #iftrue SYMBOL == N;

Work out what the condition is2.1.2 =

    if ((dir_node->dir_clarifier == IFDEF_I6RW) ||
        (dir_node->dir_clarifier == IFNDEF_I6RW)) {
        if ((dir_node->child_node == NULL) ||
            (dir_node->child_node->expression_tokens == NULL)) {
            I6Errors::issue_at_node(dir_node, I"bare '#ifdef' or '#ifndef'");
            return FALSE;
        }
        symbol_to_check = dir_node->child_node->expression_tokens->material;
    } else {
        inter_schema_node *to_eval = dir_node->child_node;
        while ((to_eval) && (to_eval->isn_type == SUBEXPRESSION_ISNT))
            to_eval = to_eval->child_node;
        if ((to_eval == NULL) || (to_eval->child_node == NULL) ||
            (to_eval->child_node->expression_tokens == NULL)) {
            I6Errors::issue_at_node(dir_node, I"malformed '#if...'");
            return FALSE;
        }
        symbol_to_check = to_eval->child_node->expression_tokens->material;
        operation_to_check = to_eval->isn_clarifier;
        value_to_check = to_eval->child_node->next_node->expression_tokens->material;
    }
    LOGIF(SCHEMA_COMPILATION, "Means checking %S\n", symbol_to_check);
    if (value_to_check) LOGIF(SCHEMA_COMPILATION, "Against %S\n", value_to_check);

This code is used in §2.1.

§2.1.3. Find out whether this symbol is defined, and if so, what its value is2.1.3 =

    if (Str::eq(symbol_to_check, I"#version_number")) { val = 8; def = TRUE; }
    else if (Str::eq(symbol_to_check, I"STRICT_MODE")) { def = TRUE; }
    else {
        identifier_finder global_finder = finder;
        IdentifierFinders::next_priority(&global_finder,
            InterPackage::scope(LargeScale::architecture_package(I)));
        inter_symbol *symb = IdentifierFinders::find(I,
            symbol_to_check, global_finder);
        symb = Wiring::cable_end(symb);
        LOGIF(SCHEMA_COMPILATION, "Symb is $3\n", symb);
        if (InterSymbol::is_defined(symb)) {
            def = TRUE;
            val = InterSymbol::evaluate_to_int(symb);
        }
    }
    LOGIF(SCHEMA_COMPILATION, "Defined: %d, value: %d\n", def, val);

This code is used in §2.1.

§2.1.4. Decide whether the condition is met or not2.1.4 =

    if ((dir_node->dir_clarifier == IFNDEF_I6RW)
        || (dir_node->dir_clarifier == IFDEF_I6RW)) decision = def;
    else {
        int h = Str::atoi(value_to_check, 0);
        LOGIF(SCHEMA_COMPILATION, "Want value %d\n", h);
        if (operation_to_check == EQ_BIP) decision = (val == h)?TRUE:FALSE;
        if (operation_to_check == NE_BIP) decision = (val != h)?TRUE:FALSE;
        if (operation_to_check == GE_BIP) decision = (val >= h)?TRUE:FALSE;
        if (operation_to_check == GT_BIP) decision = (val > h)?TRUE:FALSE;
        if (operation_to_check == LE_BIP) decision = (val <= h)?TRUE:FALSE;
        if (operation_to_check == LT_BIP) decision = (val < h)?TRUE:FALSE;
    }

    if (dir_node->dir_clarifier == IFNDEF_I6RW) decision = decision?FALSE:TRUE;
    if (dir_node->dir_clarifier == IFFALSE_I6RW) decision = decision?FALSE:TRUE;

This code is used in §2.1.

§2.1.5. Note that marking the clauses this way ensures that the next call to this function will not pick up this same conditional again. The repeated calling must therefore terminate, because the schema is finite in size and on each call returning TRUE at least 2 previously unblocked nodes are marked as blocked.

Mark the three clause nodes as blocked2.1.5 =

    dir_node->blocked_by_conditional = TRUE;
    endif_node->blocked_by_conditional = TRUE;
    if (ifnot_node) ifnot_node->blocked_by_conditional = TRUE;

This code is used in §2.1.

§2.1.6. Mark the if body as blocked2.1.6 =

    inter_schema_node *at = dir_node;
    while ((at) && (at != endif_node) && (at != ifnot_node)) {
        at->blocked_by_conditional = TRUE;
        at = at->next_node;
    }

This code is used in §2.1.

§2.1.7. Mark the if-not body as blocked2.1.7 =

    inter_schema_node *at = ifnot_node;
    while ((at) && (at != endif_node)) {
        at->blocked_by_conditional = TRUE;
        at = at->next_node;
    }

This code is used in §2.1.

§1.3. That disposes of conditional compilation: finally we can emit unconditional code. We do that with a recursive function; since the many parameters have to be passed down through each call, using the following macro makes everything easier to read. node is the current node to compile, of course; prim_cat is the "primitive category", which is Inter jargon for context.

The category at the top of the tree depends on whether we are compiling the schema in void or value context, which is signalled to us by VH. As we recurse downwards, though, the category will change. The schema print n; begins in CODE_PRIM_CAT (i.e., void context), but by the time the node for n is reached, we must be in VAL_PRIM_CAT.

define EIS_RECURSE(node, prim_cat)
     EmitInterSchemas::emit_recursively(I, node, VH, sch, opaque_state, prim_cat,
        finder, inline_command_handler, i7_source_handler);

Traverse the tree, compiling each node1.3 =

    int prim_cat = CODE_PRIM_CAT;
    if (VH->vhmode_wanted == INTER_VAL_VHMODE) prim_cat = VAL_PRIM_CAT;
    else if (VH->vhmode_wanted != INTER_VOID_VHMODE)
        internal_error("must emit schemas in INTER_VAL_VHMODE or INTER_VOID_VHMODE");

    for (inter_schema_node *node = sch->node_tree; node; node=node->next_node)
        EIS_RECURSE(node, prim_cat);

This code is used in §1.

§3. As noted, this is very much a recursive function, but it does not automatically recurse downwards: that depends on what is done at given nodes.

In particular, no children of blocked nodes — those removed by conditional compilation — are ever visited.

void EmitInterSchemas::emit_recursively(inter_tree *I, inter_schema_node *node,
    value_holster *VH, inter_schema *sch, void *opaque_state, int prim_cat,
    identifier_finder finder,
    void (*inline_command_handler)(value_holster *VH, inter_schema_token *t,
        void *opaque_state, int prim_cat, text_stream *L),
    void (*i7_source_handler)(value_holster *VH, text_stream *S,
        void *opaque_state, int prim_cat)) {
    if ((node) && (node->blocked_by_conditional == FALSE))
        Emit code for this unblocked node3.1;
}

§3.1. Emit code for this unblocked node3.1 =

    switch (node->isn_type) {
        case ASSEMBLY_ISNT: Assembly3.1.1; break;
        case CALL_ISNT: Call3.1.2; break;
        case CALLMESSAGE_ISNT: Call-message3.1.3; break;
        case CODE_ISNT: Code block3.1.4; break;
        case DIRECTIVE_ISNT: Non-conditional directive3.1.5; break;
        case EVAL_ISNT: Eval block3.1.6; break;
        case EXPRESSION_ISNT: Expression3.1.7; break;
        case LABEL_ISNT: Label3.1.8; break;
        case MESSAGE_ISNT: Message3.1.9; break;
        case OPERATION_ISNT: Operation3.1.10; break;
        case STATEMENT_ISNT: Statement3.1.11; break;
        case SUBEXPRESSION_ISNT: Subexpression3.1.12; break;
        default: internal_error("unknown schema node type");
    }

This code is used in §3.

§3.1.1. Assembly language can only appear in CODE_PRIM_CAT mode and looks like so:

    ASSEMBLY_ISNT
        EXPRESSION_ISNT
            OPCODE_ISTT "@mul"
        EXPRESSION_ISNT
            x
        EXPRESSION_ISNT
            y
        EXPRESSION_ISNT
            z

Note that recursion in VAL_PRIM_CAT mode evaluates x, y and z.

Assembly3.1.1 =

    if (prim_cat != CODE_PRIM_CAT) {  should never in fact happen
        I6Errors::issue_at_node(node, I"assembly language unexpected here");
        return;
    }
    inter_schema_node *at = node->child_node;
    if (at) {
        text_stream *opcode_text = NULL;
        if (at->isn_type == EXPRESSION_ISNT) {
            inter_schema_token *tok = at->expression_tokens;
            if ((tok->ist_type == OPCODE_ISTT) && (tok->next == NULL))
                opcode_text = tok->material;
        }
        if (opcode_text == NULL) {  should never in fact happen
            I6Errors::issue_at_node(node, I"assembly language malformed here");
            return;
        }
        Produce::inv_assembly(I, opcode_text);
        Produce::down(I);
        for (at = at->next_node; at; at=at->next_node)
            EIS_RECURSE(at, VAL_PRIM_CAT);
        Produce::up(I);
    }

This code is used in §3.1.

§3.1.2. What looks syntactically like a function call may in Inform 6 be a use of one of the "built-in functions" — for example, y = child(O). But it is not in fact a function, in the traditional Inform 6 implementation, at least; and it is not legal to perform, say, x = child; y = indirect(x, O); because child, not really being a function, has no address.

The design of Inter has gone back and forth over whether to make these Inter functions in order to simplify the picture. But if so, they are a nuisance in linking, it turns out, and so where we have ended up is that the I6 "built-in functions" are implemented by Inter primitives. It follows that a function call to them must be compiled as a special case.

Call3.1.2 =

    if (node->child_node) {
        inter_schema_token *external_tok = NULL;
        inter_schema_node *at = node->child_node;
        inter_symbol *to_call = NULL;
        inter_ti bip_for_builtin_fn = 0;
        if (at->isn_type == EXPRESSION_ISNT) {
            inter_schema_token *tok = at->expression_tokens;
            if ((tok->ist_type == IDENTIFIER_ISTT) && (tok->next == NULL))
                Work out what function or primitive to call or invoke3.1.2.1;
        }
        Compile the invocation3.1.2.2;
        Produce::down(I);
        for (; at; at=at->next_node) EIS_RECURSE(at, VAL_PRIM_CAT);
        Produce::up(I);
        if (external_tok) external_tok->ist_type = IDENTIFIER_ISTT;
    }

This code is used in §3.1.

§3.1.2.1. Inform 6 syntax is surprisingly liberal in what it allows as a function call, and the f in f(x) does not have to be a function name; it can be a variable, for example, holding the address of a function.

In the following, to_call should be set to the inter_symbol for the function to call, if the function is literally named; or bip_for_builtin_fn should be set to the primitive to invoke instead; and otherwise an indirect function call to an address will be compiled.

With one exception: the external__f(x) notation, which does not occur in I6, but permits function calls outside of the target environment. See Calling Inform from C (in inform7) for more on this. Note that although the code here appears to amend the schema by changing a token type, it is in fact changed back again very soon after.

Work out what function or primitive to call or invoke3.1.2.1 =

    if (Str::prefix_eq(tok->material, I"external__", 10)) {
        external_tok = tok;
        bip_for_builtin_fn = EXTERNALCALL_BIP;
        external_tok->ist_type = DQUOTED_ISTT;
    } else if (Str::eq(tok->material, I"random")) {
        bip_for_builtin_fn = RANDOM_BIP;
        at = at->next_node;
    } else if (Str::eq(tok->material, I"child")) {
        bip_for_builtin_fn = CHILD_BIP;
        at = at->next_node;
    } else if (Str::eq(tok->material, I"children")) {
        bip_for_builtin_fn = CHILDREN_BIP;
        at = at->next_node;
    } else if (Str::eq(tok->material, I"parent")) {
        bip_for_builtin_fn = PARENT_BIP;
        at = at->next_node;
    } else if (Str::eq(tok->material, I"sibling")) {
        bip_for_builtin_fn = SIBLING_BIP;
        at = at->next_node;
    } else if (Str::eq(tok->material, I"metaclass")) {
        bip_for_builtin_fn = METACLASS_BIP;
        at = at->next_node;
    } else if (Str::eq(tok->material, I"indirect")) {
        at = at->next_node;
    } else if (Str::eq(tok->material, I"glk")) {
        I6Errors::issue_at_node(node, I"the glk() function is now unsupported");
        return;
    } else {
        to_call = IdentifierFinders::find_token(I, tok, finder);
        if (InterSymbol::is_local(to_call)) to_call = NULL;
        if (to_call) {
            inter_tree_node *D = to_call->definition;
            if (Inode::is(D, VARIABLE_IST)) to_call = NULL;
        }
    }

This code is used in §3.1.2.

§3.1.2.2. Compile the invocation3.1.2.2 =

    if (bip_for_builtin_fn > 0) {
        Produce::inv_primitive(I, bip_for_builtin_fn);
    } else if (to_call) {
        Produce::inv_call_symbol(I, to_call);
        at = at->next_node;
    } else {
        int argc = 0;
        for (inter_schema_node *n = node->child_node; n; n=n->next_node) {
            if ((n->expression_tokens) &&
                (n->expression_tokens->inline_command == combine_ISINC)) argc++;
            argc++;
        }
        inter_ti BIP = Primitives::BIP_for_indirect_call_returning_value(argc-1);
        Produce::inv_primitive(I, BIP);
    }

This code is used in §3.1.2.

§3.1.3. This is really a simplified version of the "call" case, where we know that we have to perform indirection, i.e., call a function whose address is stored somewhere (in fact, always in a property value).

Call-message3.1.3 =

    if (node->child_node) {
        inter_schema_node *at = node->child_node;
        int argc = 0;
        for (inter_schema_node *n = node->child_node; n; n=n->next_node) argc++;
        if (argc > 4) {
            I6Errors::issue_at_node(node, I"too many arguments for call-message");
            return;
        }
        inter_ti BIP = Primitives::BIP_for_indirect_call_returning_value(argc-1);
        Produce::inv_primitive(I, BIP);
        Produce::down(I);
        for (; at; at=at->next_node) EIS_RECURSE(at, VAL_PRIM_CAT);
        Produce::up(I);
    }

This code is used in §3.1.

§3.1.4. Note that inter schemas can contain code blocks which are half-open at either end, and this enables some fruity Inform 7 inline phrase definitions. So the following can generate the equivalent of { ... or ... } as well as the more natural { ... }.

Code block3.1.4 =

    if (prim_cat != CODE_PRIM_CAT) {
        I6Errors::issue_at_node(node, I"unexpected '{ ... }' code block");
        return;
    }
    if (node->unopened == FALSE) {
        Produce::code(I);
        Produce::down(I);
    }
    for (inter_schema_node *at = node->child_node; at; at=at->next_node)
        EIS_RECURSE(at, CODE_PRIM_CAT);
    if (node->unclosed == FALSE) {
        Produce::up(I);
    }
    if (node->unopened) Produce::set_level_to_current_code_block_plus(I, 0);

This code is used in §3.1.

§3.1.5. Note that conditional directives have already been taken care of. The only other Inform 6 directive valid inside a function body is OrigSource. Therefore:

Non-conditional directive3.1.5 =

    if (node->dir_clarifier == ORIGSOURCE_I6RW) {
        OrigSource directive3.1.5.1;
    }
    else {
        I6Errors::issue_at_node(node, I"misplaced directive");
        return;
    }

This code is used in §3.1.

§3.1.5.1. OrigSource directive3.1.5.1 =

    text_stream *origfilename = NULL;
    int origlinenum = 0;
    if (node->child_node) {
        origfilename = node->child_node->expression_tokens->material;
        if (node->child_node->expression_tokens->next) {
            origlinenum = Str::atoi(node->child_node->expression_tokens->next->material, 0);
        }
    }
    Produce::provenance(I, Provenance::at_file_and_line(origfilename, origlinenum));

This code is used in §3.1.5.

§3.1.6. An EVAL_ISNT node can have any number of children, they are sequentially evaluated for their potential side-effects, but only the last produces a value.

Eval block3.1.6 =

    if ((prim_cat != CODE_PRIM_CAT) && (prim_cat != VAL_PRIM_CAT)){
        I6Errors::issue_at_node(node, I"expression in unexpected place");
        return;
    }
    if (node->child_node == NULL) Produce::val(I, K_value, InterValuePairs::number(1));
    else {
        int d = 0;
        for (inter_schema_node *at = node->child_node; at; at=at->next_node) {
            if (at->next_node) {
                d++;
                Produce::inv_primitive(I, SEQUENTIAL_BIP);
                Produce::down(I);
            }
            EIS_RECURSE(at, VAL_PRIM_CAT);
        }
        while (d > 0) { Produce::up(I); d--; }
    }

This code is used in §3.1.

§3.1.7. Note that an expression consisting only of a double-quoted text, in void context, is a print-then-print-new-line-then-return-true statement in Inform 6. This is where we detect that. (Because its meaning depends on context — i.e., it doesn't mean that in value context — we couldn't have decided this when parsing the schema.)

Expression3.1.7 =

    int serial_evaluate_us = FALSE, reference_me = FALSE, print_ret_me = FALSE;
    Decide whether exceptional expression modes apply3.1.7.1;

    if (serial_evaluate_us) { Produce::evaluation(I); Produce::down(I); }
    if (reference_me) { Produce::reference(I); Produce::down(I); }
    if (print_ret_me) {
        Produce::inv_primitive(I, PRINT_BIP);
        Produce::down(I);
    }

    for (inter_schema_token *t = node->expression_tokens; t; t=t->next)
        Evaluate this token3.1.7.2;

    if (print_ret_me) {
        Produce::up(I);
        Produce::inv_primitive(I, PRINTNL_BIP);
        Produce::rtrue(I);
    }
    if (reference_me) { Produce::up(I); }
    if (serial_evaluate_us) { Produce::up(I); }

This code is used in §3.1.

§3.1.7.1. Note that at most one of thexe exceptional cases can arise at a time.

Decide whether exceptional expression modes apply3.1.7.1 =

    int evaluations_to_perform = 0;
    for (inter_schema_token *t = node->expression_tokens; t; t=t->next)
        evaluations_to_perform++;

    if (evaluations_to_perform > 1) {
        if (prim_cat == VAL_PRIM_CAT) serial_evaluate_us = TRUE;
    } else if (evaluations_to_perform == 1) {
        if ((prim_cat == CODE_PRIM_CAT) &&
            (node->expression_tokens->ist_type == DQUOTED_ISTT))
            print_ret_me = TRUE;
    }

    if (prim_cat == REF_PRIM_CAT) reference_me = TRUE;

This code is used in §3.1.7.

§3.1.7.2. Evaluate this token3.1.7.2 =

    switch (t->ist_type) {
        case IDENTIFIER_ISTT:
            if (prim_cat == LAB_PRIM_CAT)
                Produce::lab(I, Produce::reserve_label(I, t->material));
            else
                Produce::val_symbol(I, K_value,
                    IdentifierFinders::find_token(I, t, finder));
            break;
        case ASM_ARROW_ISTT:
            Produce::assembly_marker(I, ASM_ARROW_ASMMARKER);
            break;
        case ASM_SP_ISTT:
            Produce::assembly_marker(I, ASM_SP_ASMMARKER);
            break;
        case ASM_NEGATED_LABEL_ISTT:
            if (Str::eq(t->material, I"rtrue"))
                Produce::assembly_marker(I, ASM_NEG_RTRUE_ASMMARKER);
            else if (Str::eq(t->material, I"rfalse"))
                Produce::assembly_marker(I, ASM_NEG_RFALSE_ASMMARKER);
            else {
                Produce::assembly_marker(I, ASM_NEG_ASMMARKER);
                Produce::lab(I, Produce::reserve_label(I, t->material));
            }
            break;
        case ASM_LABEL_ISTT:
            if (Str::eq(t->material, I"rtrue"))
                Produce::assembly_marker(I, ASM_RTRUE_ASMMARKER);
            else if (Str::eq(t->material, I"rfalse"))
                Produce::assembly_marker(I, ASM_RFALSE_ASMMARKER);
            else
                Produce::lab(I, Produce::reserve_label(I, t->material));
            break;
        case NUMBER_ISTT:
        case BIN_NUMBER_ISTT:
        case HEX_NUMBER_ISTT: {
            inter_pair val;
            if (t->constant_number >= 0) {
                val = InterValuePairs::number((inter_ti) t->constant_number);
            } else {
                val = InterValuePairs::number_from_I6_notation(t->material);
                if (InterValuePairs::is_undef(val)) {
                    TEMPORARY_TEXT(msg)
                    WRITE_TO(msg, "malformed literal number '%S'", t->material);
                    I6Errors::issue_at_node(node, msg);
                    DISCARD_TEXT(msg)
                    return;
                }
            }
            Produce::val(I, K_value, val);
            break;
        }
        case REAL_NUMBER_ISTT:
            Produce::val_real_from_text(I, t->material);
            break;
        case DQUOTED_ISTT:
            Produce::val_text(I, t->material);
            break;
        case SQUOTED_ISTT:
            if (Str::len(t->material) == 1) {
                Produce::val_char(I, Str::get_at(t->material, 0));
            } else {
                Produce::val_dword(I, t->material);
            }
            break;
        case I7_ISTT:
            if (i7_source_handler)
                (*i7_source_handler)(VH, t->material, opaque_state, prim_cat);
            break;
        case INLINE_ISTT:
            if (inline_command_handler)
                (*inline_command_handler)(VH, t, opaque_state, prim_cat, NULL);
            break;
        default: {
            TEMPORARY_TEXT(msg)
            WRITE_TO(msg, "'%S' was unexpected in expression context", t->material);
            I6Errors::issue_at_node(node, msg);
            DISCARD_TEXT(msg)
            break;
        }
    }

This code is used in §3.1.7.

§3.1.8. A twig for a label, such as:

    LABEL_ISNT
        EXPRESSION_ISNT
            MyLabel

This places the label MyLabel at the current write position.

What makes this more complicated is that an inline command might be being used to determine the name of that label, and/or to amend a label numbering counter. For example, the schema .{-label:Say}{-counter-up:Say}; results in:

    LABEL_ISNT
        EXPRESSION_ISNT
            INLINE_ISNT = label:Say
        EXPRESSION_ISNT
            INLINE_ISNT = counter-up:Say

Label3.1.8 =

    if (prim_cat != CODE_PRIM_CAT) {
        I6Errors::issue_at_node(node, I"label in unexpected place");
        return;
    }
    TEMPORARY_TEXT(L)
    WRITE_TO(L, ".");
    for (inter_schema_node *at = node->child_node; at; at=at->next_node) {
        for (inter_schema_token *t = at->expression_tokens; t; t=t->next) {
            if (t->ist_type == IDENTIFIER_ISTT) {
                WRITE_TO(L, "%S", t->material);
            } else if ((t->ist_type == INLINE_ISTT) &&
                    ((t->inline_command == label_ISINC) ||
                     (t->inline_command == counter_up_ISINC) ||
                     (t->inline_command == counter_down_ISINC))) {
                value_holster VN = Holsters::new(INTER_DATA_VHMODE);
                if (inline_command_handler)
                    (*inline_command_handler)(&VN, t, opaque_state, VAL_PRIM_CAT, L);
            } else {
                TEMPORARY_TEXT(msg)
                WRITE_TO(msg, "expected label name but found '%S'", t->material);
                I6Errors::issue_at_node(node, msg);
                DISCARD_TEXT(msg)
                return;
            }
        }
    }
    Produce::place_label(I, Produce::reserve_label(I, L));
    DISCARD_TEXT(L)

This code is used in §3.1.

§3.1.9. Message3.1.9 =

    inter_schema_node *at = node->child_node;
    if (at) {
        int argc = 0;
        for (inter_schema_node *n = at; n; n=n->next_node) argc++;
        inter_ti BIP = Primitives::BIP_for_message_send(argc);
        Produce::inv_primitive(I, BIP);
        Produce::down(I);
        for (; at; at=at->next_node) EIS_RECURSE(at, VAL_PRIM_CAT);
        Produce::up(I);
    }

This code is used in §3.1.

§3.1.10. Note the three pseudo-operations here — that is, operators which do not directly correspond to Inter primitives. They are:

● HAS_XBIP, which is done by performing a property lookup;
● HASNT_XBIP, which is done by negating the same;
● OWNERKIND_XBIP, which is a way to finesse that PROPERTYVALUE_BIP is ternary at the Inter level, but only binary in Inform 6 source code. When the code writes obj.prop, this is treated here as if it had been OBJECT_TY>>obj.prop; so the value OBJECT_TY is dropped in. But if the author had written K>>obj.prop — giving the full ternary form — we suppress the >> operator and take K, obj, prop as the three arguments to the primitive PROPERTYVALUE_BIP. (>> has no other purpose or use, and is not present in standard Inform 6 syntax.)

Operation3.1.10 =

    inter_ti op = node->isn_clarifier;
    if ((op == HAS_XBIP) || (op == HASNT_XBIP)) op = PROPERTYVALUE_BIP;

    int reference_me = FALSE, negate_me = FALSE, insert_OBJECT_TY = FALSE, nop_me = FALSE;
    Decide whether exceptional operator modes apply3.1.10.1;

    if (reference_me) {
        Produce::reference(I);
        Produce::down(I);
    }
    if (negate_me) {
        Produce::inv_primitive(I, NOT_BIP);
        Produce::down(I);
    }
    if (nop_me == FALSE) {
        Produce::inv_primitive(I, op);
        Produce::down(I);
    }
    Operands3.1.10.2;
    if (nop_me == FALSE) { Produce::up(I); }
    if (negate_me) { Produce::up(I); }
    if (reference_me) { Produce::up(I); }

This code is used in §3.1.

§3.1.10.1. Decide whether exceptional operator modes apply3.1.10.1 =

    if (prim_cat == REF_PRIM_CAT) reference_me = TRUE;
    if (node->isn_clarifier == HASNT_XBIP) negate_me = TRUE;
    if ((op == PROPERTYEXISTS_BIP) || (op == PROPERTYVALUE_BIP) ||
        (op == PROPERTYARRAY_BIP) || (op == PROPERTYLENGTH_BIP)) {
        if ((node->child_node->isn_type != OPERATION_ISNT) ||
            (node->child_node->isn_clarifier != OWNERKIND_XBIP))
            insert_OBJECT_TY = TRUE;
    }
    if (op == OWNERKIND_XBIP) nop_me = TRUE;

This code is used in §3.1.10.

§3.1.10.2. Operands3.1.10.2 =

    if (insert_OBJECT_TY) {
        inter_symbol *OBJECT_TY_s =
            IdentifierFinders::find(I, I"OBJECT_TY", finder);
        Produce::val_symbol(I, K_value, OBJECT_TY_s);
    }
    int pc = VAL_PRIM_CAT;
    if (Primitives::term_category(node->isn_clarifier, 0) == REF_PRIM_CAT)
        pc = REF_PRIM_CAT;
    EIS_RECURSE(node->child_node, pc);
    if (I6Operators::arity(node->isn_clarifier) == 2)
        EIS_RECURSE(node->child_node->next_node, VAL_PRIM_CAT);

This code is used in §3.1.10.

§3.1.11. The pseudo-statement READ_XBIP is handled as the assembly language @aread. We don't want to regard keyboard input as being a core feature of the Inter instruction set, but rather as something available on some platforms and not on others.

Statement3.1.11 =

    if (prim_cat != CODE_PRIM_CAT) {
        I6Errors::issue_at_node(node, I"statement in unexpected place");
        return;
    }
    if (node->isn_clarifier == CASE_BIP) Produce::set_level_to_current_code_block_plus(I, 2);
    if (node->isn_clarifier == READ_XBIP) Produce::inv_assembly(I, I"@aread");
    else Produce::inv_primitive(I, node->isn_clarifier);
    if (node->isn_clarifier == OBJECTLOOP_BIP) {
        Handle OBJECTLOOP as a special case3.1.11.1;
    } else {
        int arity = Primitives::term_count(node->isn_clarifier);
        if (arity > 0) {
            Produce::down(I);
            inter_schema_node *at = node->child_node;
            inter_schema_node *last = NULL;
            for (int i = 0; ((at) && (i<arity)); i++) {
                EIS_RECURSE(at, Primitives::term_category(node->isn_clarifier, i));
                last = at;
                at = at->next_node;
            }
            if (!((last) && (last->unclosed))) Produce::up(I);
        }
    }

This code is used in §3.1.

§3.1.11.1. As noted in Inter Primitives, the signature of OBJECTLOOP_BIP is ref val val code -> void, so it needs four operands:

(1) The ref is the variable.
(2) The first val is the object class it ranges over. If we are unable to narrow this down, we will simply make that Object, the result being a potentially slow loop over all objects.
(3) The second val is condition which must apply to any given x for the code block to be executed.
(4) The code is the code block.

But it arrives here not with four child nodes, but just two, corresponding to the second val and the code respectively. We must find the first two as subexpressions of the first child, by directly probing its subtree. Consider these possibilities:

    objectloop (x) { ... }
                |  \ code
                ref and second val; first val is "Object"

    objectloop (x ofclass K1_thing) { ... }
                |            |         |
                ref       first val   code
               --------------------
                    second val

    objectloop ((x ofclass K1_thing) && (x has container)) { ... }
                 |             |                              |
                 ref       first val                         code
               -------------------------------------------
                               second val

Handle OBJECTLOOP as a special case3.1.11.1 =

    Produce::down(I);
    inter_schema_node *oc_node = node->child_node;
    while ((oc_node) &&
        ((oc_node->isn_type != OPERATION_ISNT) ||
        (oc_node->isn_clarifier != OFCLASS_BIP)))
        oc_node = oc_node->child_node;
    if (oc_node) {
        inter_schema_node *var_node = oc_node->child_node;
        inter_schema_node *cl_node = var_node?(var_node->next_node):NULL;
        if ((var_node) && (cl_node)) {
            EIS_RECURSE(var_node, REF_PRIM_CAT);
            EIS_RECURSE(cl_node, VAL_PRIM_CAT);
        } else {
            I6Errors::issue_at_node(node, I"malformed 'objectloop' header");
            return;
        }
    } else {
        inter_schema_node *var_node = node->child_node;
        while ((var_node) && (var_node->isn_type != EXPRESSION_ISNT))
            var_node = var_node->child_node;
        if ((var_node) && (var_node->expression_tokens) &&
            ((var_node->expression_tokens->ist_type == IDENTIFIER_ISTT) ||
                (var_node->expression_tokens->ist_type == INLINE_ISTT))) {
            EIS_RECURSE(var_node, REF_PRIM_CAT);
            Produce::val_symbol(I, K_value, IdentifierFinders::find(I, I"Object", finder));
        } else {
            I6Errors::issue_at_node(node, I"'objectloop' without visible variable");
            return;
        }
    }
    inter_schema_node *at = node->child_node;
    EIS_RECURSE(at, VAL_PRIM_CAT);
    at = at->next_node;
    EIS_RECURSE(at, CODE_PRIM_CAT);
    if (at->unclosed == FALSE) Produce::up(I);

This code is used in §3.1.11.

§3.1.12. Last and least: a subexpression node gives one or more nodes to be evaluated, and if there's more than one, we use the SEQUENTIAL_BIP operator (which is like the comma in C) to throw away the results of the non-final evaluations.

Subexpression3.1.12 =

    int d = 0;
    for (inter_schema_node *at = node->child_node; at; at=at->next_node) {
        if (at->next_node) {
            d++;
            Produce::inv_primitive(I, SEQUENTIAL_BIP);
            Produce::down(I);
        }
        EIS_RECURSE(at, prim_cat);
    }
    while (d > 0) { Produce::up(I); d--; }

This code is used in §3.1.