typedef struct {
/* always tag_header(SBUF_TYPE) */
CELL header;
/* tagged */
CELL top;
CELL string;
} F_SBUF;
F_SBUF* sbuf(F_FIXNUM capacity);
void primitive_sbuf(void);
void fixup_sbuf(F_SBUF* sbuf);
void collect_sbuf(F_SBUF* sbuf);