To compile specifications of values into Inter value opcodes or array entries.

• §1. Introduction
• §2. An API for compiling values
• §6. Implementation

§1. Introduction. Quite a range of data can be held as specifications: see Specifications (in values). Inside the compiler these are stored as parse_node pointers. This section of code aims to provide a single unified way to compile values, even though:

• ● We may need to compile either an array entry or an Inter val opcode. We abstract this using Value Holsters (in building), holders into which compiled values are placed.
• ● We sometimes need to compile a value which needs to be converted to a different kind first, a process called "casting".
• ● Sometimes a fresh copy of a value is needed, and sometimes a reference to its existing copy.

This complexity was historically managed by having persistent "compilation modes" which Inform would enter for short periods and then exit, and during which specifications would compile difficulty. This had worked well enough since 2005 but by the 2020s there were 12 different modes, making in principle 1024 different combinations to worry over. Because modes were entered and exited far away from their consequences, and in dozens of different parts of the compiler, it became difficult to reason with any confidence about what would happen, so worrying was about all that could be done.

In April 2021, all modes were removed except compile_spec_in_constant_mode, and even that one is relatively benign: entry and exit into it is managed automatically by the code below, so that the rest of Inform no longer needs to think about compilation modes at all.

int compile_spec_in_constant_mode = FALSE;
int CompileValues::compiling_in_constant_mode?Usage of CompileValues::compiling_in_constant_mode:
Compile Rvalues - §2(void) {
    return compile_spec_in_constant_mode;
}

§2. An API for compiling values. When the rest of Inform wants to compile a value, it should call one of the following functions.

To begin with, compiling to array entries:

void CompileValues::to_array_entry_of_kind(parse_node *value, kind *K_wanted) {
    CompileValues::to_array_entry(
        CompileValues::cast_constant(value, K_wanted));
}

void CompileValues::to_array_entry(parse_node *value) {
    value_holster VH = Holsters::new(INTER_DATA_VHMODE);
    CompileValues::to_holster(&VH, value, COMPILE_SPEC_AS_CONSTANT);
    inter_pair val = Holsters::unholster_to_pair(&VH);
    EmitArrays::generic_entry(val);
}

§3. Now constants, which can be compiled either to a holster or to a pair of inter_t numbers. Use the latter as little as possible.

void CompileValues::constant_to_holster(value_holster *VH, parse_node *value,
    kind *K_wanted) {
    CompileValues::to_holster(VH,
        CompileValues::cast_constant(value, K_wanted), COMPILE_SPEC_AS_CONSTANT);
}

inter_pair CompileValues::constant_to_pair(parse_node *value, kind *K_wanted) {
    value_holster VH = Holsters::new(INTER_DATA_VHMODE);
    CompileValues::constant_to_holster(&VH, value, K_wanted);
    return Holsters::unholster_to_pair(&VH);
}

§4. A general method (i.e., not restricted to constant context) for compiling to a pair value. Use this as little as possible.

inter_pair CompileValues::to_pair?Usage of CompileValues::to_pair:
Compile Invocations Inline - §11.1(parse_node *spec) {
    value_holster VH = Holsters::new(INTER_DATA_VHMODE);
    CompileValues::to_holster(&VH, spec, COMPILE_SPEC_AS_VALUE);
    return Holsters::unholster_to_pair(&VH);
}

§5. Finally, for compiling to Inter opcodes in a val context — in other words, for values as they appear in imperative code rather than in data structures. A "fresh" value should be made when we want the value compiled to be a new, independent copy of the data in question. Consider:

    let T be { 2, 3, 5, 7 };
    let U be T;
    add 11 to T;

Clearly U must be set to a fresh copy of the data in T, not a reference to the same data. So the T in line 2 must be compiled as "fresh", whereas the T in line 3 must not.

void CompileValues::to_code_val?Usage of CompileValues::to_code_val:
Compile Rvalues - §1.3
Compile Lvalues - §1.3, §1.3.2, §1.4, §2
Compile Conditions - §1, §1.1, §1.2
Matching Action Patterns - §3.5.1.1.1.25, §5, §5.2.1, §5.2.2, §5.2.3
Compile Loops - §1.2, §2, §4
Deciding to Defer - §4.2, §15, §17, §18, §20, §21, §22
Cinders and Deferrals - §4
Compile Invocations As Calls - §3
Compile Invocations Inline - §11, §12
Compile Solutions to Equations - §4(parse_node *value) {
    CompileValues::to_code_val_inner(value, NULL, COMPILE_SPEC_AS_VALUE);
}
void CompileValues::to_code_val_of_kind?Usage of CompileValues::to_code_val_of_kind:
Compile Rvalues - §6
Compile Schemas - §3.2, §5.2
Compile Blocks and Lines - §4.4.5.2, §4.4.5.5, §4.4.5.1.2
Compile Invocations Inline - §6.1.1.3, §6.1.1.4.9, §6.1.1.4.10, §6.6.10, §6.6.10.1, §6.6.10.2, §6.6.10.3
Compile Arithmetic - §2(parse_node *value, kind *K) {
    CompileValues::to_code_val_inner(value, K, COMPILE_SPEC_AS_VALUE);
}
void CompileValues::to_fresh_code_val_of_kind?Usage of CompileValues::to_fresh_code_val_of_kind:
Compile Schemas - §3.2, §5.2
Compile Invocations - §1.3.1.2.1.2
Compile Invocations As Calls - §2.2
Compile Invocations Inline - §6.1.1.3, §6.1.1.4.7.1(parse_node *value, kind *K) {
    CompileValues::to_code_val_inner(value, K, COMPILE_SPEC_AS_FRESH_VALUE);
}
void CompileValues::to_code_val_inner(parse_node *value, kind *K, int how) {
    int down = FALSE;
    if (K) value = CompileValues::cast_nonconstant(value, K, &down);
    value_holster VH = Holsters::new(INTER_VAL_VHMODE);
    CompileValues::to_holster(&VH, value, how);
    if (down) EmitCode::up();
}

§6. Implementation. All of the functions in the above API make use of these private ones:

define COMPILE_SPEC_AS_CONSTANT    1
define COMPILE_SPEC_AS_VALUE       2
define COMPILE_SPEC_AS_FRESH_VALUE 3

void CompileValues::to_holster?Usage of CompileValues::to_holster:
§2, §3, §4, §5(value_holster *VH, parse_node *value, int how) {
    switch (how) {
        case COMPILE_SPEC_AS_CONSTANT:
            LOGIF(EXPRESSIONS, "Compiling (const): $P\n", value); break;
        case COMPILE_SPEC_AS_VALUE:
            LOGIF(EXPRESSIONS, "Compiling (value): $P\n", value); break;
        case COMPILE_SPEC_AS_FRESH_VALUE:
            LOGIF(EXPRESSIONS, "Compiling (fresh): $P\n", value); break;
    }
    int s = compile_spec_in_constant_mode;
    if (how == COMPILE_SPEC_AS_CONSTANT) compile_spec_in_constant_mode = TRUE;
    else compile_spec_in_constant_mode = FALSE;
    LOG_INDENT;
    Take care of any freshness6.1;
    LOG_OUTDENT;
    compile_spec_in_constant_mode = s;
}

§6.1. This implements "fresh" mode. For regular values like numbers there's no difference, but if our value is a block value such as a list then we evaluate to a copy of it, not to the original. Making that copy means calling CopyPV at runtime, so it cannot be done in a data holster (i.e., when VH is an INTER_DATA_VHMODE holster).

Take care of any freshness6.1 =

    value = NonlocalVariables::substitute_constants(value);
    kind *K_found = Specifications::to_kind(value);
    CompileValues::note_that_kind_is_used(K_found);
    int made_fresh = FALSE;
    if (how == COMPILE_SPEC_AS_FRESH_VALUE) {
        if (VH->vhmode_wanted == INTER_DATA_VHMODE)
            internal_error("must compile by reference in INTER_DATA_VHMODE");
        kind *K = Specifications::to_kind(value);
        if ((K) && (Kinds::Behaviour::uses_block_values(K))) {
            EmitCode::call(Hierarchy::find(COPYPV_HL));
            EmitCode::down();
                Frames::emit_new_local_value(K);
            made_fresh = TRUE;
        }
    }
    Actually compile6.1.1;
    if (made_fresh) {
        EmitCode::up();
    }

• This code is used in §6.

§6.1.1. Actually compile6.1.1 =

    if (Lvalues::is_lvalue(value)) {
        CompileLvalues::in_rvalue_context(VH, value);
    } else if (Rvalues::is_rvalue(value)) {
        CompileRvalues::compile(VH, value);
        if ((VH->vhmode_provided == INTER_DATA_VHMODE) &&
            (VH->vhmode_wanted == INTER_VAL_VHMODE)) {
            Holsters::unholster_to_code_val(Emit::tree(), VH);
        }
    } else if (Specifications::is_condition(value)) {
        CompileConditions::compile(VH, value);
    }

• This code is used in §6.1.

§7. "Casting" is converting a value of one kind to a value of another but which has the same meaning, give or take. In a constant context, the main cast we can perform is from literal K_number values like 31 to turn them into literal K_real_number values, a process called "promotion".

parse_node *CompileValues::cast_constant?Usage of CompileValues::cast_constant:
§2, §3, §8(parse_node *value, kind *K_wanted) {
    value = NonlocalVariables::substitute_constants(value);
    CompileValues::note_that_kind_is_used(K_wanted);
    value = LiteralReals::promote_number_if_necessary(value, K_wanted);
    kind *K_found = Specifications::to_kind(value);
    if ((K_understanding) &&
        (Kinds::eq(K_wanted, K_understanding)) && (Kinds::eq(K_found, K_text)))
        Node::set_kind_of_value(value, K_understanding);
    return value;
}

§8. In a value context we can additionally compile code to perform the conversion at runtime, which extends the range of promotions we can make.

parse_node *CompileValues::cast_nonconstant?Usage of CompileValues::cast_nonconstant:
§5(parse_node *value, kind *K_wanted,
    int *down) {
    if (Node::is(value, TABLE_ENTRY_NT) == FALSE) {
        value = CompileValues::cast_constant(value, K_wanted);
        kind *K_found = Specifications::to_kind(value);
        CompileValues::note_that_kind_is_used(K_found);
        EmitCode::casting_call(K_found, K_wanted, down);
    }
    return value;
}

§9. Certain kinds of value cannot be used on every virtual machine; for example, the Z-machine does not support real numbers.

int VM_non_support_problem_issued = FALSE;
void CompileValues::note_that_kind_is_used?Usage of CompileValues::note_that_kind_is_used:
§6.1, §7, §8(kind *K) {
    if (CompileValues::target_VM_supports_kind(K) == FALSE) {
        if (VM_non_support_problem_issued == FALSE) {
            VM_non_support_problem_issued = TRUE;
            StandardProblems::handmade_problem(Task::syntax_tree(),
                _p_(PM_KindRequiresGlulx));
            Problems::quote_source(1, current_sentence);
            Problems::quote_kind(2, K);
            Problems::issue_problem_segment(
                "You wrote %1, but with the settings for this project as they are, "
                "I'm unable to make use of %2. (Try changing to Glulx on the Settings "
                "panel; that should fix it.)");
            Problems::issue_problem_end();

        }
    }
}

int CompileValues::target_VM_supports_kind(kind *K) {
    target_vm *VM = Task::vm();
    if (VM == NULL) internal_error("target VM not set yet");
    if ((Kinds::FloatingPoint::uses_floating_point(K)) &&
        (TargetVMs::supports_floating_point(VM) == FALSE)) return FALSE;
    return TRUE;
}