akbasic/src/value.c

/**
 * @file value.c
 * @brief Implements the BASIC value type and its operators.
 *
 * Ported from basicvalue.go. It used to reproduce the reference's arithmetic
 * oddities deliberately, because the golden corpus encoded the observed
 * behaviour; TODO.md section 0.1 retired that constraint and section 6 records
 * which ones have since been fixed and why.
 */

#include <inttypes.h>
#include <stdio.h>
#include <string.h>

#include <akerror.h>
#include <akstdlib.h>

#include <akbasic/error.h>
#include <akbasic/value.h>

/*
 * Selected on the type, not summed. The reference adds both numeric fields --
 * `rval.intval + int64(rval.floatval)` -- which happens to give the right answer
 * only because whichever field is unused is always zero (TODO.md section 6
 * item 5). Nothing enforces that: a value that ever carries both, or one reused
 * from the pool without being zeroed, silently computes the sum of the two.
 */
static int64_t rval_as_int(akbasic_Value *rval)
{
    if ( rval->valuetype == AKBASIC_TYPE_FLOAT ) {
	return (int64_t)rval->floatval;
    }
    if ( rval->valuetype == AKBASIC_TYPE_BOOLEAN ) {
	return rval->boolvalue;
    }
    return rval->intval;
}

/** @brief The float counterpart of rval_as_int(); same reasoning. */
static double rval_as_float(akbasic_Value *rval)
{
    if ( rval->valuetype == AKBASIC_TYPE_FLOAT ) {
	return rval->floatval;
    }
    if ( rval->valuetype == AKBASIC_TYPE_BOOLEAN ) {
	return (double)rval->boolvalue;
    }
    return (double)rval->intval;
}

/**
 * @brief What a value's type is called in a diagnostic.
 *
 * Indexed by akbasic_Type, so a new type added to the enum without a row here
 * trips the negative-array-size assert below rather than printing an empty
 * string into an error message nobody can act on.
 */
static const char *TYPE_NAMES[] = {
    "an undefined value",	/* AKBASIC_TYPE_UNDEFINED */
    "an integer",		/* AKBASIC_TYPE_INTEGER   */
    "a float",			/* AKBASIC_TYPE_FLOAT     */
    "a string",			/* AKBASIC_TYPE_STRING    */
    "a truth value",		/* AKBASIC_TYPE_BOOLEAN   */
    "a structure",		/* AKBASIC_TYPE_STRUCT    */
    "a pointer"			/* AKBASIC_TYPE_POINTER   */
};

typedef char akbasic_assert_type_names_complete
    [(sizeof(TYPE_NAMES) / sizeof(TYPE_NAMES[0]) == AKBASIC_TYPE_POINTER + 1) ? 1 : -1];

static const char *type_name(akbasic_Type valuetype)
{
    if ( valuetype < 0 || valuetype > AKBASIC_TYPE_POINTER ) {
	return "a value of unknown type";
    }
    return TYPE_NAMES[valuetype];
}

/**
 * @brief Refuse an operand the numeric path cannot read.
 *
 * `math_minus`, `math_multiply` and `math_divide` are shaped
 * `if ( INTEGER ) ... else <treat as float>`, and **that else is a catch-all
 * rather than a float branch**: it reads `floatval` from whatever it is handed.
 * A truth value carries its payload in `boolvalue` and leaves `floatval` zero,
 * so `(A# == 1) - 1` computed `0 - 1` into a field nothing reads, left the type
 * as BOOLEAN, and printed `true` instead of -2. Multiplication and division did
 * the same; only `math_plus` escaped, because it enumerates its cases and ends
 * in an error.
 *
 * Checked here rather than in each operator so there is one rule and one
 * message, and so a type added later is refused by all three at once instead of
 * silently taking the float branch in each.
 *
 * **The two operands have different rules, and deliberately.** The left one
 * decides the branch, so it must be a number. The right one is read through
 * rval_as_int()/rval_as_float(), which handle a truth value on purpose -- a
 * comparison yields -1 or 0 and `5 - (A# == 1)` is 6, which is the same property
 * that lets `AND` and `OR` double as logical operators. Refusing a truth value
 * on the right would break that, so this permits exactly what those two readers
 * can actually read and nothing else.
 */
static akerr_ErrorContext *require_numeric(akbasic_Value *self, akbasic_Value *rval, const char *what)
{
    PREPARE_ERROR(errctx);

    FAIL_ZERO_RETURN(errctx,
		     (self->valuetype == AKBASIC_TYPE_INTEGER ||
		      self->valuetype == AKBASIC_TYPE_FLOAT),
		     AKBASIC_ERR_TYPE, "Cannot perform %s on %s", what, type_name(self->valuetype));
    FAIL_ZERO_RETURN(errctx,
		     (rval->valuetype == AKBASIC_TYPE_INTEGER ||
		      rval->valuetype == AKBASIC_TYPE_FLOAT ||
		      rval->valuetype == AKBASIC_TYPE_BOOLEAN),
		     AKBASIC_ERR_TYPE, "Cannot perform %s on %s", what, type_name(rval->valuetype));
    SUCCEED_RETURN(errctx);
}

/* Copy a string into a value's inline buffer. Truncation is an error. */
static akerr_ErrorContext *set_string(akbasic_Value *dest, const char *src)
{
    PREPARE_ERROR(errctx);
    size_t srclen = 0;

    PASS(errctx, aksl_strlen(src, &srclen));
    FAIL_ZERO_RETURN(errctx, (srclen < AKBASIC_MAX_STRING_LENGTH),
		     AKBASIC_ERR_VALUE,
		     "String result of %zu characters exceeds the %d character limit",
		     srclen, AKBASIC_MAX_STRING_LENGTH - 1);
    /* aksl_strcpy always terminates and refuses rather than truncates, which is
       the behaviour this site already wanted. The length check above stays
       because it names the limit in the message. */
    PASS(errctx, aksl_strcpy(dest->stringval, sizeof(dest->stringval), src));
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_valuepool_init(akbasic_ValuePool *obj)
{
    PREPARE_ERROR(errctx);

    FAIL_ZERO_RETURN(errctx, (obj != NULL), AKERR_NULLPOINTER, "NULL pool in init");
    PASS(errctx, aksl_memset(obj, 0, sizeof(*obj)));
    obj->next = 0;
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_valuepool_take(akbasic_ValuePool *obj, int count, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);
    int i = 0;

    FAIL_ZERO_RETURN(errctx, (obj != NULL), AKERR_NULLPOINTER, "NULL pool in take");
    FAIL_ZERO_RETURN(errctx, (dest != NULL), AKERR_NULLPOINTER, "NULL destination in take");
    FAIL_ZERO_RETURN(errctx, (count > 0), AKBASIC_ERR_BOUNDS,
		     "Array element count %d must be positive", count);
    FAIL_ZERO_RETURN(errctx, (count <= AKBASIC_MAX_ARRAY_VALUES - obj->next),
		     AKBASIC_ERR_BOUNDS,
		     "Array of %d elements does not fit in the %d remaining value slots",
		     count, AKBASIC_MAX_ARRAY_VALUES - obj->next);

    *dest = &obj->values[obj->next];
    for ( i = 0; i < count; i++ ) {
	PASS(errctx, akbasic_value_zero(&obj->values[obj->next + i]));
    }
    obj->next += count;
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_init(akbasic_Value *obj)
{
    PREPARE_ERROR(errctx);

    FAIL_ZERO_RETURN(errctx, (obj != NULL), AKERR_NULLPOINTER, "NULL value in init");
    /*
     * BasicValue.init() is empty in the reference; the zeroing happens in
     * zero(). Keeping both means the call sites port one-for-one.
     */
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_zero(akbasic_Value *obj)
{
    PREPARE_ERROR(errctx);

    FAIL_ZERO_RETURN(errctx, (obj != NULL), AKERR_NULLPOINTER, "NULL value in zero");
    obj->valuetype = AKBASIC_TYPE_UNDEFINED;
    obj->stringval[0] = '\0';
    obj->mutable_ = false;
    obj->intval = 0;
    obj->floatval = 0.0;
    obj->boolvalue = AKBASIC_FALSE;
    obj->structtype = -1;
    obj->structbase = NULL;
    obj->hostbase = NULL;
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_clone(akbasic_Value *self, akbasic_Value *dest)
{
    PREPARE_ERROR(errctx);

    FAIL_ZERO_RETURN(errctx, (self != NULL), AKERR_NULLPOINTER, "NULL source in clone");
    FAIL_ZERO_RETURN(errctx, (dest != NULL), AKERR_NULLPOINTER, "NULL destination in clone");

    if ( self == dest ) {
	SUCCEED_RETURN(errctx);
    }
    dest->valuetype = self->valuetype;
    PASS(errctx, aksl_memcpy(dest->stringval, self->stringval, sizeof(dest->stringval)));
    dest->intval = self->intval;
    dest->floatval = self->floatval;
    dest->boolvalue = self->boolvalue;
    /*
     * The structure reference copies with everything else, and for a POINTER
     * that is exactly right -- copying a pointer copies what it points at, not
     * what it points to. For a STRUCT it is *not* the copy the language
     * promises: assignment intercepts before it gets here and copies the slots
     * instead. Cloning the reference is still correct at this level, because
     * this is the one-slot copy and a structure does not fit in one slot.
     */
    dest->structtype = self->structtype;
    dest->structbase = self->structbase;
    dest->hostbase = self->hostbase;
    /* mutable_ is deliberately not copied: the reference's clone() does not. */
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_to_string(akbasic_Value *self, char *dest, size_t len)
{
    PREPARE_ERROR(errctx);
    int written = 0;

    FAIL_ZERO_RETURN(errctx, (self != NULL), AKERR_NULLPOINTER, "NULL value in to_string");
    FAIL_ZERO_RETURN(errctx, (dest != NULL), AKERR_NULLPOINTER, "NULL destination in to_string");
    FAIL_ZERO_RETURN(errctx, (len > 0), AKBASIC_ERR_BOUNDS, "Zero-length destination in to_string");

    switch ( self->valuetype ) {
    case AKBASIC_TYPE_STRING:
	PASS(errctx, aksl_snprintf(&written, dest, len, "%s", self->stringval));
	break;
    case AKBASIC_TYPE_INTEGER:
	PASS(errctx, aksl_snprintf(&written, dest, len, "%" PRId64, self->intval));
	break;
    case AKBASIC_TYPE_FLOAT:
	PASS(errctx, aksl_snprintf(&written, dest, len, "%f", self->floatval));
	break;
    case AKBASIC_TYPE_BOOLEAN:
	/* Go's %t, which is "true"/"false" and not the numeric -1/0. */
	PASS(errctx, aksl_snprintf(&written, dest, len, "%s",
				   (self->boolvalue == AKBASIC_TRUE ? "true" : "false")));
	break;
    default:
	PASS(errctx, aksl_snprintf(&written, dest, len, "(UNDEFINED STRING REPRESENTATION FOR %d)",
				   (int)self->valuetype));
	break;
    }
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_set_bool(akbasic_Value *obj, bool result)
{
    PREPARE_ERROR(errctx);

    FAIL_ZERO_RETURN(errctx, (obj != NULL), AKERR_NULLPOINTER, "NULL value in set_bool");
    obj->valuetype = AKBASIC_TYPE_BOOLEAN;
    obj->boolvalue = (result ? AKBASIC_TRUE : AKBASIC_FALSE);
    SUCCEED_RETURN(errctx);
}

bool akbasic_value_is_true(akbasic_Value *self)
{
    if ( self == NULL || self->valuetype != AKBASIC_TYPE_BOOLEAN ) {
	return false;
    }
    return (self->boolvalue == AKBASIC_TRUE);
}

bool akbasic_value_is_truthy(akbasic_Value *self)
{
    if ( self == NULL ) {
	return false;
    }
    /*
     * Nonzero is true, which is Commodore's rule rather than a convenience.
     * BASIC 7.0 has no separate boolean type: a comparison yields -1 or 0, `AND`
     * and `OR` are the bitwise operators, and `IF A THEN` is legal for any
     * numeric A. Testing only for the boolean type would make `IF A# THEN` and
     * `IF A = 1 OR B = 2 THEN` -- whose OR yields an integer -- both silently
     * false.
     *
     * A string is never true. A C128 raises a type mismatch instead; that is a
     * stricter answer this interpreter could adopt later, and false is the
     * conservative one meanwhile.
     */
    switch ( self->valuetype ) {
    case AKBASIC_TYPE_BOOLEAN:
	return (self->boolvalue != 0);
    case AKBASIC_TYPE_POINTER:
	/*
	 * **A pointer is true when it points at something**, which is what makes
	 * `IF P@ THEN` the way to ask. Without it there is no way to test for the
	 * end of a list at all: comparing a pointer to 0 reads a numeric field it
	 * does not carry and answers whatever that field happened to hold.
	 *
	 * A *structure* is deliberately not given a truth value. It always
	 * exists, so the question has no answer worth guessing at, and falling
	 * through to false keeps `IF A@ THEN` from quietly meaning something.
	 */
	return (self->structbase != NULL);
    case AKBASIC_TYPE_INTEGER:
	return (self->intval != 0);
    case AKBASIC_TYPE_FLOAT:
	return (self->floatval != 0.0);
    default:
	return false;
    }
}

/* Shared prologue for the unary operators: validate, clone into scratch. */
static akerr_ErrorContext *unary_prologue(akbasic_Value *self, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);

    FAIL_ZERO_RETURN(errctx, (self != NULL), AKERR_NULLPOINTER, "NULL value in unary operation");
    FAIL_ZERO_RETURN(errctx, (scratch != NULL), AKERR_NULLPOINTER, "NULL scratch in unary operation");
    FAIL_ZERO_RETURN(errctx, (dest != NULL), AKERR_NULLPOINTER, "NULL destination in unary operation");
    PASS(errctx, akbasic_value_clone(self, scratch));
    *dest = scratch;
    SUCCEED_RETURN(errctx);
}

/* Shared prologue for the binary operators: validate, clone into scratch. */
static akerr_ErrorContext *binary_prologue(akbasic_Value *self, akbasic_Value *rval, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);

    FAIL_ZERO_RETURN(errctx, (self != NULL), AKERR_NULLPOINTER, "NULL value in binary operation");
    FAIL_ZERO_RETURN(errctx, (rval != NULL), AKERR_NULLPOINTER, "nil rval");
    FAIL_ZERO_RETURN(errctx, (scratch != NULL), AKERR_NULLPOINTER, "NULL scratch in binary operation");
    FAIL_ZERO_RETURN(errctx, (dest != NULL), AKERR_NULLPOINTER, "NULL destination in binary operation");
    PASS(errctx, akbasic_value_clone(self, scratch));
    *dest = scratch;
    SUCCEED_RETURN(errctx);
}

/**
 * @brief The integer a bitwise operator should use for @p value.
 *
 * BOOLEAN counts as an integer here, and that is what makes `AND` and `OR`
 * double as logical operators. Commodore BASIC has no separate logical pair: it
 * represents true as -1, every bit set, precisely so that `A = 1 AND B = 2`
 * works out bit by bit and lands on -1 or 0. Refusing a boolean operand would
 * make the commonest conditional in the language a type error.
 */
static bool bitwise_operand(akbasic_Value *value, int64_t *dest)
{
    if ( value == NULL ) {
	return false;
    }
    if ( value->valuetype == AKBASIC_TYPE_INTEGER ) {
	*dest = value->intval;
	return true;
    }
    if ( value->valuetype == AKBASIC_TYPE_BOOLEAN ) {
	*dest = value->boolvalue;
	return true;
    }
    return false;
}

akerr_ErrorContext *akbasic_value_invert(akbasic_Value *self, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);

    FAIL_ZERO_RETURN(errctx, (self != NULL), AKERR_NULLPOINTER, "NULL value in invert");
    FAIL_NONZERO_RETURN(errctx, (self->valuetype == AKBASIC_TYPE_STRING),
			AKBASIC_ERR_TYPE, "Cannot invert a string");
    PASS(errctx, unary_prologue(self, scratch, dest));
    (*dest)->intval = -(self->intval);
    (*dest)->floatval = -(self->floatval);
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_bitwise_not(akbasic_Value *self, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);
    int64_t a = 0;

    FAIL_ZERO_RETURN(errctx, (self != NULL), AKERR_NULLPOINTER, "NULL value in bitwise not");
    FAIL_ZERO_RETURN(errctx, bitwise_operand(self, &a), AKBASIC_ERR_TYPE,
		     "Can only perform bitwise operations on integers and truth values");
    PASS(errctx, unary_prologue(self, scratch, dest));
    /*
     * A truth value inverts to a truth value. On a C128 true is -1 -- every bit
     * set -- so `NOT` of it is 0 and `NOT` of 0 is -1 either way you compute it;
     * carrying the type through is what keeps `IF NOT (A = 9) THEN` reading as a
     * condition rather than as an integer that happens to be nonzero.
     */
    (*dest)->valuetype = self->valuetype;
    (*dest)->intval = ~a;
    (*dest)->boolvalue = ~a;
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_shift_left(akbasic_Value *self, int64_t bits, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);

    FAIL_ZERO_RETURN(errctx, (self != NULL), AKERR_NULLPOINTER, "NULL value in shift left");
    FAIL_ZERO_RETURN(errctx, (self->valuetype == AKBASIC_TYPE_INTEGER),
		     AKBASIC_ERR_TYPE, "Only integer datatypes can be bit-shifted");
    /*
     * Go's << on a negative or >=64 count is defined; C's is undefined. Refuse
     * rather than inherit the UB -- no golden case exercises it, so this cannot
     * change observed behaviour.
     */
    FAIL_ZERO_RETURN(errctx, (bits >= 0 && bits < 64), AKBASIC_ERR_VALUE,
		     "Shift count %" PRId64 " is out of range 0..63", bits);
    PASS(errctx, unary_prologue(self, scratch, dest));
    (*dest)->intval = (int64_t)((uint64_t)(*dest)->intval << bits);
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_shift_right(akbasic_Value *self, int64_t bits, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);

    FAIL_ZERO_RETURN(errctx, (self != NULL), AKERR_NULLPOINTER, "NULL value in shift right");
    FAIL_ZERO_RETURN(errctx, (self->valuetype == AKBASIC_TYPE_INTEGER),
		     AKBASIC_ERR_TYPE, "Only integer datatypes can be bit-shifted");
    FAIL_ZERO_RETURN(errctx, (bits >= 0 && bits < 64), AKBASIC_ERR_VALUE,
		     "Shift count %" PRId64 " is out of range 0..63", bits);
    PASS(errctx, unary_prologue(self, scratch, dest));
    (*dest)->intval = (*dest)->intval >> bits;
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_bitwise_and(akbasic_Value *self, akbasic_Value *rval, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);
    int64_t a = 0;
    int64_t b = 0;

    FAIL_ZERO_RETURN(errctx, (self != NULL), AKERR_NULLPOINTER, "NULL value in bitwise and");
    FAIL_ZERO_RETURN(errctx, (rval != NULL), AKERR_NULLPOINTER, "nil rval");
    FAIL_ZERO_RETURN(errctx, (bitwise_operand(self, &a) && bitwise_operand(rval, &b)),
		     AKBASIC_ERR_TYPE,
		     "Can only perform bitwise operations on integers and truth values");
    PASS(errctx, binary_prologue(self, rval, scratch, dest));
    (*dest)->valuetype = AKBASIC_TYPE_INTEGER;
    (*dest)->intval = a & b;
    (*dest)->boolvalue = (*dest)->intval;
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_bitwise_or(akbasic_Value *self, akbasic_Value *rval, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);
    int64_t a = 0;
    int64_t b = 0;

    FAIL_ZERO_RETURN(errctx, (self != NULL), AKERR_NULLPOINTER, "NULL value in bitwise or");
    FAIL_ZERO_RETURN(errctx, (rval != NULL), AKERR_NULLPOINTER, "nil rval");
    FAIL_ZERO_RETURN(errctx, (bitwise_operand(self, &a) && bitwise_operand(rval, &b)),
		     AKBASIC_ERR_TYPE,
		     "Can only perform bitwise operations on integers and truth values");
    PASS(errctx, binary_prologue(self, rval, scratch, dest));
    (*dest)->valuetype = AKBASIC_TYPE_INTEGER;
    (*dest)->intval = a | b;
    (*dest)->boolvalue = (*dest)->intval;
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_bitwise_xor(akbasic_Value *self, akbasic_Value *rval, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);
    int64_t a = 0;
    int64_t b = 0;

    FAIL_ZERO_RETURN(errctx, (self != NULL), AKERR_NULLPOINTER, "NULL value in bitwise xor");
    FAIL_ZERO_RETURN(errctx, (rval != NULL), AKERR_NULLPOINTER, "nil rval");
    FAIL_ZERO_RETURN(errctx, (bitwise_operand(self, &a) && bitwise_operand(rval, &b)),
		     AKBASIC_ERR_TYPE,
		     "Can only perform bitwise operations on integers and truth values");
    PASS(errctx, binary_prologue(self, rval, scratch, dest));
    (*dest)->valuetype = AKBASIC_TYPE_INTEGER;
    (*dest)->intval = a ^ b;
    (*dest)->boolvalue = (*dest)->intval;
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_math_plus(akbasic_Value *self, akbasic_Value *rval, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);
    akbasic_Value *out = NULL;
    char buf[AKBASIC_MAX_STRING_LENGTH * 2];
    int written = 0;

    FAIL_ZERO_RETURN(errctx, (self != NULL), AKERR_NULLPOINTER, "NULL value in math plus");
    FAIL_ZERO_RETURN(errctx, (rval != NULL), AKERR_NULLPOINTER, "nil rval");
    FAIL_ZERO_RETURN(errctx, (scratch != NULL), AKERR_NULLPOINTER, "NULL scratch in math plus");
    FAIL_ZERO_RETURN(errctx, (dest != NULL), AKERR_NULLPOINTER, "NULL destination in math plus");

    /*
     * Always a clone, like every other operator. The reference mutates `self` in
     * place when it happens to be mutable, so `A# + 1` modified `A#` whenever
     * the left operand came from a variable rather than from a literal --
     * TODO.md section 6 item 4, and the highest-blast-radius entry on that list.
     *
     * It was load-bearing: NEXT advanced its counter by calling this and letting
     * the mutation land in the variable. NEXT now writes the result back itself,
     * which is what made this safe to change. tests/for_next.c is the coverage
     * that had to exist first.
     */
    PASS(errctx, akbasic_value_clone(self, scratch));
    out = scratch;

    if ( self->valuetype == AKBASIC_TYPE_INTEGER ) {
	out->intval = self->intval + rval_as_int(rval);
    } else if ( self->valuetype == AKBASIC_TYPE_FLOAT ) {
	out->floatval = self->floatval + rval_as_float(rval);
    } else if ( self->valuetype == AKBASIC_TYPE_STRING && rval->valuetype == AKBASIC_TYPE_STRING ) {
	PASS(errctx, aksl_snprintf(&written, buf, sizeof(buf), "%s%s",
				   self->stringval, rval->stringval));
	PASS(errctx, set_string(out, buf));
    } else if ( self->valuetype == AKBASIC_TYPE_STRING && rval->valuetype == AKBASIC_TYPE_INTEGER ) {
	PASS(errctx, aksl_snprintf(&written, buf, sizeof(buf), "%s%" PRId64,
				   self->stringval, rval->intval));
	PASS(errctx, set_string(out, buf));
    } else if ( self->valuetype == AKBASIC_TYPE_STRING && rval->valuetype == AKBASIC_TYPE_FLOAT ) {
	PASS(errctx, aksl_snprintf(&written, buf, sizeof(buf), "%s%f",
				   self->stringval, rval->floatval));
	PASS(errctx, set_string(out, buf));
    } else {
	FAIL_RETURN(errctx, AKBASIC_ERR_TYPE, "Invalid arithmetic operation");
    }
    *dest = out;
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_math_minus(akbasic_Value *self, akbasic_Value *rval, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);

    PASS(errctx, binary_prologue(self, rval, scratch, dest));
    FAIL_NONZERO_RETURN(errctx,
			(self->valuetype == AKBASIC_TYPE_STRING || rval->valuetype == AKBASIC_TYPE_STRING),
			AKBASIC_ERR_TYPE, "Cannot perform subtraction on strings");
    PASS(errctx, require_numeric(self, rval, "subtraction"));
    if ( self->valuetype == AKBASIC_TYPE_INTEGER ) {
	(*dest)->intval = self->intval - rval_as_int(rval);
    } else {
	(*dest)->floatval = self->floatval - rval_as_float(rval);
    }
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_math_divide(akbasic_Value *self, akbasic_Value *rval, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);

    PASS(errctx, binary_prologue(self, rval, scratch, dest));
    FAIL_NONZERO_RETURN(errctx,
			(self->valuetype == AKBASIC_TYPE_STRING || rval->valuetype == AKBASIC_TYPE_STRING),
			AKBASIC_ERR_TYPE, "Cannot perform division on strings");
    PASS(errctx, require_numeric(self, rval, "division"));
    if ( self->valuetype == AKBASIC_TYPE_INTEGER ) {
	/*
	 * Integer division by zero is UB in C where Go panics. Neither is
	 * acceptable in a library, and no golden case divides by zero, so raise.
	 */
	FAIL_NONZERO_RETURN(errctx, (rval_as_int(rval) == 0), AKBASIC_ERR_VALUE,
			    "DIVISION BY ZERO");
	(*dest)->intval = self->intval / rval_as_int(rval);
    } else {
	(*dest)->floatval = self->floatval / rval_as_float(rval);
    }
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_math_multiply(akbasic_Value *self, akbasic_Value *rval, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);
    char buf[AKBASIC_MAX_STRING_LENGTH];
    int64_t i = 0;
    size_t srclen = 0;
    size_t offset = 0;

    PASS(errctx, binary_prologue(self, rval, scratch, dest));

    if ( self->valuetype == AKBASIC_TYPE_STRING ) {
	FAIL_NONZERO_RETURN(errctx, (rval->valuetype == AKBASIC_TYPE_STRING),
			    AKBASIC_ERR_TYPE, "String multiplication requires an integer multiple");
	/*
	 * Go's strings.Repeat panics on a negative count. Refusing is strictly
	 * better than either panicking or reading off the end of the buffer, and
	 * no golden case does it.
	 */
	FAIL_NONZERO_RETURN(errctx, (rval->intval < 0), AKBASIC_ERR_VALUE,
			    "String multiplier %" PRId64 " must not be negative", rval->intval);
	PASS(errctx, aksl_strlen((*dest)->stringval, &srclen));
	FAIL_NONZERO_RETURN(errctx,
			    (srclen != 0 && (uint64_t)rval->intval > (AKBASIC_MAX_STRING_LENGTH - 1) / srclen),
			    AKBASIC_ERR_VALUE,
			    "Repeated string of %zu x %" PRId64 " characters exceeds the %d character limit",
			    srclen, rval->intval, AKBASIC_MAX_STRING_LENGTH - 1);
	for ( i = 0; i < rval->intval; i++ ) {
	    PASS(errctx, aksl_memcpy(buf + offset, (*dest)->stringval, srclen));
	    offset += srclen;
	}
	buf[offset] = '\0';
	PASS(errctx, set_string(*dest, buf));
	SUCCEED_RETURN(errctx);
    }
    /*
     * The reference falls through to the numeric branches even for a string,
     * where self->floatval is 0 and the write lands in a field nothing reads.
     * That was reproduced deliberately and is now a return, because the guard
     * below would otherwise refuse the string repeat this branch just did --
     * and the fallthrough was only ever provably harmless, never useful.
     */
    PASS(errctx, require_numeric(self, rval, "multiplication"));
    if ( self->valuetype == AKBASIC_TYPE_INTEGER ) {
	(*dest)->intval = self->intval * rval_as_int(rval);
    } else {
	(*dest)->floatval = self->floatval * rval_as_float(rval);
    }
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_less_than(akbasic_Value *self, akbasic_Value *rval, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);
    int cmp = 0;

    PASS(errctx, binary_prologue(self, rval, scratch, dest));
    if ( self->valuetype == AKBASIC_TYPE_INTEGER ) {
	PASS(errctx, akbasic_value_set_bool(*dest, self->intval < rval_as_int(rval)));
    } else if ( self->valuetype == AKBASIC_TYPE_FLOAT ) {
	PASS(errctx, akbasic_value_set_bool(*dest, self->floatval < rval_as_float(rval)));
    } else {
	PASS(errctx, aksl_strcmp(self->stringval, rval->stringval, &cmp));
	PASS(errctx, akbasic_value_set_bool(*dest, cmp < 0));
    }
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_less_than_equal(akbasic_Value *self, akbasic_Value *rval, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);
    int cmp = 0;

    PASS(errctx, binary_prologue(self, rval, scratch, dest));
    if ( self->valuetype == AKBASIC_TYPE_INTEGER ) {
	PASS(errctx, akbasic_value_set_bool(*dest, self->intval <= rval_as_int(rval)));
    } else if ( self->valuetype == AKBASIC_TYPE_FLOAT ) {
	PASS(errctx, akbasic_value_set_bool(*dest, self->floatval <= rval_as_float(rval)));
    } else {
	PASS(errctx, aksl_strcmp(self->stringval, rval->stringval, &cmp));
	PASS(errctx, akbasic_value_set_bool(*dest, cmp <= 0));
    }
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_greater_than(akbasic_Value *self, akbasic_Value *rval, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);
    int cmp = 0;

    PASS(errctx, binary_prologue(self, rval, scratch, dest));
    if ( self->valuetype == AKBASIC_TYPE_INTEGER ) {
	PASS(errctx, akbasic_value_set_bool(*dest, self->intval > rval_as_int(rval)));
    } else if ( self->valuetype == AKBASIC_TYPE_FLOAT ) {
	PASS(errctx, akbasic_value_set_bool(*dest, self->floatval > rval_as_float(rval)));
    } else {
	PASS(errctx, aksl_strcmp(self->stringval, rval->stringval, &cmp));
	PASS(errctx, akbasic_value_set_bool(*dest, cmp > 0));
    }
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_greater_than_equal(akbasic_Value *self, akbasic_Value *rval, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);
    int cmp = 0;

    PASS(errctx, binary_prologue(self, rval, scratch, dest));
    if ( self->valuetype == AKBASIC_TYPE_INTEGER ) {
	PASS(errctx, akbasic_value_set_bool(*dest, self->intval >= rval_as_int(rval)));
    } else if ( self->valuetype == AKBASIC_TYPE_FLOAT ) {
	PASS(errctx, akbasic_value_set_bool(*dest, self->floatval >= rval_as_float(rval)));
    } else {
	PASS(errctx, aksl_strcmp(self->stringval, rval->stringval, &cmp));
	PASS(errctx, akbasic_value_set_bool(*dest, cmp >= 0));
    }
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_is_equal(akbasic_Value *self, akbasic_Value *rval, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);
    int cmp = 0;

    PASS(errctx, binary_prologue(self, rval, scratch, dest));
    if ( self->valuetype == AKBASIC_TYPE_INTEGER ) {
	PASS(errctx, akbasic_value_set_bool(*dest, self->intval == rval_as_int(rval)));
    } else if ( self->valuetype == AKBASIC_TYPE_FLOAT ) {
	PASS(errctx, akbasic_value_set_bool(*dest, self->floatval == rval_as_float(rval)));
    } else {
	PASS(errctx, aksl_strcmp(self->stringval, rval->stringval, &cmp));
	PASS(errctx, akbasic_value_set_bool(*dest, cmp == 0));
    }
    SUCCEED_RETURN(errctx);
}

akerr_ErrorContext *akbasic_value_is_not_equal(akbasic_Value *self, akbasic_Value *rval, akbasic_Value *scratch, akbasic_Value **dest)
{
    PREPARE_ERROR(errctx);
    int cmp = 0;

    PASS(errctx, binary_prologue(self, rval, scratch, dest));
    if ( self->valuetype == AKBASIC_TYPE_INTEGER ) {
	PASS(errctx, akbasic_value_set_bool(*dest, self->intval != rval_as_int(rval)));
    } else if ( self->valuetype == AKBASIC_TYPE_FLOAT ) {
	PASS(errctx, akbasic_value_set_bool(*dest, self->floatval != rval_as_float(rval)));
    } else {
	PASS(errctx, aksl_strcmp(self->stringval, rval->stringval, &cmp));
	PASS(errctx, akbasic_value_set_bool(*dest, cmp != 0));
    }
    SUCCEED_RETURN(errctx);
}