bc: partially rewrite parser, tests pass, ^C might be broken now

The entire control construct (if/while/for/funcdef) or {} block is
"eaten" by the corresponding parsing function, instead of maintaining
special "block flag stack" with magic bits in it, and returning to main
input loop after every inner statement (every input line, essentially).

This required moving line input deep into lexer - now zbc_lex_next()
triggers more reading when needed.

"block flag stack" is gone.

Correctness of ^C handling wasn't checked, might need fixing now.

if/else syntax is changed to match GNU bc: "else" can not be on
the next line (the rationale is that "if (1) 2" statement in interactive
mode should execute and print 2 instead of waiting for possible
"else ..." line).

This change fixes the following examples:

if (1) if (1) 1 else 2 else 3

if (0) 1 else if (1) 2

define w() { auto z; return 1; }

function                                             old     new   delta
zbc_parse_stmt_possibly_auto                           -    2232   +2232
zbc_vm_process                                        89     561    +472
zbc_lex_next                                        1982    2296    +314
bc_vm_init                                           749     757      +8
bc_parse_expr_empty_ok                              2016    2021      +5
bc_num_printNewline                                   54      51      -3
zbc_program_read                                     289     280      -9
bc_parse_free                                         47      38      -9
bc_parse_reset                                       126     113     -13
bc_parse_create                                      108      92     -16
bc_parse_push_block_flag                              47       -     -47
bc_parse_noElse                                       48       -     -48
zbc_parse_text_init                                  113      59     -54
zbc_parse_body                                       121       -    -121
zbc_parse_else                                       125       -    -125
zbc_parse_endBody                                    254       -    -254
bc_vm_run                                            421     134    -287
zbc_parse_auto                                       290       -    -290
zcommon_parse                                        476       -    -476
zbc_parse_stmt                                      1682       7   -1675
------------------------------------------------------------------------------
(add/remove: 1/7 grow/shrink: 4/8 up/down: 3031/-3427)       Total: -396 bytes
   text	   data	    bss	    dec	    hex	filename
 982586	    485	   7296	 990367	  f1c9f	busybox_old
 982138	    485	   7296	 989919	  f1adf	busybox_unstripped

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 260 insertions, 371 deletions

diff --git a/miscutils/bc.c b/miscutils/bc.c
index 374279889..95ba8b094 100644
--- a/miscutils/bc.c
+++ b/miscutils/bc.c
@@ -171,7 +171,7 @@
 #define DEBUG_EXEC  0
 
 #if DEBUG_LEXER
-static unsigned lex_indent;
+static uint8_t lex_indent;
 #define dbg_lex(...) \
 	do { \
 		fprintf(stderr, "%*s", lex_indent, ""); \
@@ -558,19 +558,16 @@ enum {
 #endif
 
 typedef struct BcLex {
-
 	const char *buf;
 	size_t i;
 	size_t line;
 	size_t len;
 	bool newline;
-
 	struct {
 		BcLexType t;
 		BcLexType last;
 		BcVec v;
 	} t;
-
 } BcLex;
 
 #define BC_PARSE_STREND              ((char) UCHAR_MAX)
@@ -581,37 +578,9 @@ typedef struct BcLex {
 #define BC_PARSE_NOREAD              (1 << 3)
 #define BC_PARSE_ARRAY               (1 << 4)
 
-#define BC_PARSE_TOP_FLAG_PTR(parse) ((parse)->bf_top)
-#define BC_PARSE_TOP_FLAG(parse)     (*(BC_PARSE_TOP_FLAG_PTR(parse)))
-#define BC_PARSE_FLAG_STACK_EMPTY(p) ((p)->bf_top == (p)->bf_base)
-
-#define BC_PARSE_FLAG_FUNC_INNER     (1 << 0)
-#define BC_PARSE_FLAG_FUNC           (1 << 1)
-#define BC_PARSE_FLAG_BODY           (1 << 2)
-#define BC_PARSE_FLAG_LOOP           (1 << 3)
-#define BC_PARSE_FLAG_LOOP_INNER     (1 << 4)
-#define BC_PARSE_FLAG_IF             (1 << 5)
-#define BC_PARSE_FLAG_ELSE           (1 << 6)
-#define BC_PARSE_FLAG_IF_END         (1 << 7)
-
-// If we have none of the above bits, we can stop parsing and execute already parsed chunk
-#define BC_PARSE_CAN_EXEC(parse)     (BC_PARSE_TOP_FLAG(parse) == 0)
-
-#define BC_PARSE_FUNC_INNER(parse)   (BC_PARSE_TOP_FLAG(parse) & BC_PARSE_FLAG_FUNC_INNER)
-#define BC_PARSE_FUNC(parse)         (BC_PARSE_TOP_FLAG(parse) & BC_PARSE_FLAG_FUNC)
-#define BC_PARSE_BODY(parse)         (BC_PARSE_TOP_FLAG(parse) & BC_PARSE_FLAG_BODY)
-#define BC_PARSE_LOOP(parse)         (BC_PARSE_TOP_FLAG(parse) & BC_PARSE_FLAG_LOOP)
-#define BC_PARSE_LOOP_INNER(parse)   (BC_PARSE_TOP_FLAG(parse) & BC_PARSE_FLAG_LOOP_INNER)
-#define BC_PARSE_IF(parse)           (BC_PARSE_TOP_FLAG(parse) & BC_PARSE_FLAG_IF)
-#define BC_PARSE_ELSE(parse)         (BC_PARSE_TOP_FLAG(parse) & BC_PARSE_FLAG_ELSE)
-#define BC_PARSE_IF_END(parse)       (BC_PARSE_TOP_FLAG(parse) & BC_PARSE_FLAG_IF_END)
-
 typedef struct BcParse {
 	BcLex l;
 
-	uint8_t *bf_base;
-	uint8_t *bf_top;
-
 	BcVec exits;
 	BcVec conds;
 
@@ -620,9 +589,8 @@ typedef struct BcParse {
 	BcFunc *func;
 	size_t fidx;
 
+//TODO: needed? Example?
 	size_t nbraces;
-//FIXME: "define w(x) { auto z; return 1; }" fails to parse
-	bool auto_part;
 } BcParse;
 
 typedef struct BcProgram {
@@ -666,26 +634,6 @@ typedef struct BcProgram {
 
 } BcProgram;
 
-static void bc_parse_push_block_flag(BcParse *p, uint8_t flags)
-{
-	size_t size;
-	uint8_t *flag_ptr = BC_PARSE_TOP_FLAG_PTR(p);
-	flags |= (*flag_ptr & (BC_PARSE_FLAG_FUNC | BC_PARSE_FLAG_LOOP));
-	flags |= BC_PARSE_FLAG_BODY;
-
-	size = p->bf_top - p->bf_base;
-	p->bf_base = xrealloc(p->bf_base, size + 2);
-	p->bf_top = p->bf_base + size + 1;
-	dbg_lex("%s:%d pushed block flag lvl:%d bits:0x%02x", __func__, __LINE__, size + 1, flags);
-	*p->bf_top = flags;
-}
-
-static ALWAYS_INLINE void bc_parse_pop_block_flag(BcParse *p)
-{
-	p->bf_top--;
-	dbg_lex("%s:%d popped block flag lvl:%d bits:0x%02x", __func__, __LINE__, p->bf_top - p->bf_base, *p->bf_top);
-}
-
 #define BC_PROG_STACK(s, n) ((s)->len >= ((size_t) n))
 
 #define BC_PROG_MAIN (0)
@@ -747,6 +695,7 @@ struct globals {
 	IF_FEATURE_BC_SIGNALS(smallint ttyin;)
 	IF_FEATURE_CLEAN_UP(smallint exiting;)
 	smallint in_read;
+	smallint use_stdin;
 
 	BcParse prs;
 	BcProgram prog;
@@ -756,6 +705,7 @@ struct globals {
 	unsigned err_line;
 
 	BcVec files;
+	BcVec stdin_buffer;
 
 	char *env_args;
 
@@ -1052,6 +1002,7 @@ static void quit(void)
 	if (ferror(stdin))
 		bb_perror_msg_and_die("input error");
 	fflush_and_check();
+	dbg_exec("quit(): exiting with exitcode SUCCESS");
 	exit(0);
 }
 
@@ -2955,6 +2906,79 @@ static BC_STATUS zcommon_lex_token(BcLex *l)
 	IF_DC(RETURN_STATUS(zdc_lex_token(l));)
 }
 
+static bool bc_lex_more_input(BcLex *l)
+{
+	size_t str;
+	bool comment;
+
+	bc_vec_pop_all(&G.stdin_buffer);
+
+	// This loop is complex because the vm tries not to send any lines that end
+	// with a backslash to the parser. The reason for that is because the parser
+	// treats a backslash+newline combo as whitespace, per the bc spec. In that
+	// case, and for strings and comments, the parser will expect more stuff.
+	comment = false;
+	str = 0;
+	for (;;) {
+		size_t prevlen = G.stdin_buffer.len;
+		char *string;
+
+		bc_read_line(&G.stdin_buffer);
+		// No more input means EOF
+		if (G.stdin_buffer.len <= prevlen + 1) // (we expect +1 for NUL byte)
+			break;
+
+		string = G.stdin_buffer.v + prevlen;
+		while (*string) {
+			char c = *string;
+			if (string == G.stdin_buffer.v || string[-1] != '\\') {
+				if (IS_BC)
+					str ^= (c == '"');
+				else {
+					if (c == ']')
+						str -= 1;
+					else if (c == '[')
+						str += 1;
+				}
+			}
+			string++;
+			if (c == '/' && *string == '*') {
+				comment = true;
+				string++;
+				continue;
+			}
+			if (c == '*' && *string == '/') {
+				comment = false;
+				string++;
+			}
+		}
+		if (str != 0 || comment) {
+			G.stdin_buffer.len--; // backstep over the trailing NUL byte
+			continue;
+		}
+
+		// Check for backslash+newline.
+		// we do not check that last char is '\n' -
+		// if it is not, then it's EOF, and looping back
+		// to bc_read_line() will detect it:
+		string -= 2;
+		if (string >= G.stdin_buffer.v && *string == '\\') {
+			G.stdin_buffer.len--;
+			continue;
+		}
+
+		break;
+	}
+
+	l->buf = G.stdin_buffer.v;
+	l->i = 0;
+//bb_error_msg("G.stdin_buffer.len:%d '%s'", G.stdin_buffer.len, G.stdin_buffer.v);
+	l->len = G.stdin_buffer.len - 1; // do not include NUL
+
+	G.use_stdin = (l->len != 0);
+	return G.use_stdin;
+}
+
 static BC_STATUS zbc_lex_next(BcLex *l)
 {
 	BcStatus s;
@@ -2964,10 +2988,16 @@ static BC_STATUS zbc_lex_next(BcLex *l)
 
 	l->line += l->newline;
 	G.err_line = l->line;
-	l->t.t = BC_LEX_EOF;
 
+	l->t.t = BC_LEX_EOF;
+//this NL handling is bogus
 	l->newline = (l->i == l->len);
-	if (l->newline) RETURN_STATUS(BC_STATUS_SUCCESS);
+	if (l->newline) {
+		if (!G.use_stdin || !bc_lex_more_input(l))
+			RETURN_STATUS(BC_STATUS_SUCCESS);
+		// here it's guaranteed that l->i is below l->len
+		l->newline = false;
+	}
 
 	// Loop until failure or we don't have whitespace. This
 	// is so the parser doesn't get inundated with whitespace.
@@ -3528,19 +3558,8 @@ static BC_STATUS zcommon_parse(BcParse *p)
 
 static BC_STATUS zbc_parse_text_init(BcParse *p, const char *text)
 {
-	BcStatus s;
-
 	p->func = bc_program_func(p->fidx);
 
-	if (!text[0] && !BC_PARSE_CAN_EXEC(p)) {
-		p->l.t.t = BC_LEX_INVALID;
-		s = BC_STATUS_SUCCESS;
-		ERROR_RETURN(s =) zcommon_parse(p);
-		if (s) RETURN_STATUS(s);
-		if (!BC_PARSE_CAN_EXEC(p))
-			RETURN_STATUS(bc_error("file is not executable"));
-	}
-
 	RETURN_STATUS(zbc_lex_text_init(&p->l, text));
 }
 #if ERRORS_ARE_FATAL
@@ -3580,9 +3599,8 @@ static void bc_parse_reset(BcParse *p)
 
 	p->l.i = p->l.len;
 	p->l.t.t = BC_LEX_EOF;
-	p->auto_part = (p->nbraces = 0);
+	p->nbraces = 0;
 
-	p->bf_top = p->bf_base; // pop all flags
 	bc_vec_pop_all(&p->exits);
 	bc_vec_pop_all(&p->conds);
 	bc_vec_pop_all(&p->ops);
@@ -3592,7 +3610,6 @@ static void bc_parse_reset(BcParse *p)
 
 static void bc_parse_free(BcParse *p)
 {
-	free(p->bf_base);
 	bc_vec_free(&p->exits);
 	bc_vec_free(&p->conds);
 	bc_vec_free(&p->ops);
@@ -3604,12 +3621,11 @@ static void bc_parse_create(BcParse *p, size_t func)
 	memset(p, 0, sizeof(BcParse));
 
 	bc_lex_init(&p->l);
-	p->bf_top = p->bf_base = xzalloc(1);
 	bc_vec_init(&p->exits, sizeof(BcInstPtr), NULL);
 	bc_vec_init(&p->conds, sizeof(size_t), NULL);
 	bc_vec_init(&p->ops, sizeof(BcLexType), NULL);
 
-	// p->auto_part = p->nbraces = 0; - already is
+	// p->nbraces = 0; - already is
 	bc_parse_updateFunc(p, func);
 }
 
@@ -3625,14 +3641,20 @@ static void bc_parse_create(BcParse *p, size_t func)
 // first in the expr enum. Note: This only works for binary operators.
 #define BC_TOKEN_2_INST(t) ((char) ((t) - BC_LEX_NEG + BC_INST_NEG))
 
-static BC_STATUS zbc_parse_else(BcParse *p);
-static BC_STATUS zbc_parse_stmt(BcParse *p);
+static BC_STATUS zbc_parse_stmt_possibly_auto(BcParse *p, bool auto_allowed);
 static BC_STATUS zbc_parse_expr(BcParse *p, uint8_t flags, BcParseNext next);
 static BcStatus bc_parse_expr_empty_ok(BcParse *p, uint8_t flags, BcParseNext next);
 #if ERRORS_ARE_FATAL
-# define zbc_parse_else(...) (zbc_parse_else(__VA_ARGS__), BC_STATUS_SUCCESS)
-# define zbc_parse_stmt(...) (zbc_parse_stmt(__VA_ARGS__), BC_STATUS_SUCCESS)
 # define zbc_parse_expr(...) (zbc_parse_expr(__VA_ARGS__), BC_STATUS_SUCCESS)
+# defone zbc_parse_stmt_possibly_auto(...) (zbc_parse_stmt_possibly_auto(__VA_ARGS__), BC_STATUS_SUCCESS)
+#endif
+
+static BC_STATUS zbc_parse_stmt(BcParse *p)
+{
+	RETURN_STATUS(zbc_parse_stmt_possibly_auto(p, false));
+}
+#if ERRORS_ARE_FATAL
+# define zbc_parse_stmt(...) (zbc_parse_stmt(__VA_ARGS__), BC_STATUS_SUCCESS)
 #endif
 
 static void bc_parse_operator(BcParse *p, BcLexType type, size_t start,
@@ -4037,7 +4059,7 @@ static BC_STATUS zbc_parse_return(BcParse *p)
 	BcLexType t;
 	bool paren;
 
-	if (!BC_PARSE_FUNC(p)) RETURN_STATUS(bc_error_bad_token());
+	dbg_lex_enter("%s:%d entered", __func__, __LINE__);
 
 	s = zbc_lex_next(&p->l);
 	if (s) RETURN_STATUS(s);
@@ -4063,97 +4085,62 @@ static BC_STATUS zbc_parse_return(BcParse *p)
 		bc_parse_push(p, BC_INST_RET);
 	}
 
+	dbg_lex_done("%s:%d done", __func__, __LINE__);
 	RETURN_STATUS(s);
 }
 #if ERRORS_ARE_FATAL
 # define zbc_parse_return(...) (zbc_parse_return(__VA_ARGS__), BC_STATUS_SUCCESS)
 #endif
 
-static BC_STATUS zbc_parse_endBody(BcParse *p)
+static void bc_parse_noElse(BcParse *p)
 {
-	BcStatus s = BC_STATUS_SUCCESS;
-
-	if (BC_PARSE_FLAG_STACK_EMPTY(p))
-		RETURN_STATUS(bc_error_bad_token());
-
-	if (BC_PARSE_IF(p)) {
-		uint8_t *flag_ptr;
+	BcInstPtr *ip;
+	size_t *label;
 
-		while (p->l.t.t == BC_LEX_NLINE) {
-			s = zbc_lex_next(&p->l);
-			if (s) RETURN_STATUS(s);
-		}
+	ip = bc_vec_top(&p->exits);
+	label = bc_vec_item(&p->func->labels, ip->idx);
+	dbg_lex("%s:%d rewriting label: %d -> %d", __func__, __LINE__, *label, p->func->code.len);
+	*label = p->func->code.len;
 
-		bc_parse_pop_block_flag(p);
+	bc_vec_pop(&p->exits);
+}
 
-		flag_ptr = BC_PARSE_TOP_FLAG_PTR(p);
-		dbg_lex("%s:%d setting BC_PARSE_FLAG_IF_END bit", __func__, __LINE__);
-		*flag_ptr = (*flag_ptr | BC_PARSE_FLAG_IF_END);
+static BC_STATUS zbc_parse_else(BcParse *p)
+{
+	BcStatus s;
+	BcInstPtr ip;
 
-		if (p->l.t.t == BC_LEX_KEY_ELSE)
-			s = zbc_parse_else(p);
-	}
-	else if (BC_PARSE_ELSE(p)) {
-		BcInstPtr *ip;
-		size_t *label;
+	dbg_lex_enter("%s:%d entered", __func__, __LINE__);
 
-		ip = bc_vec_top(&p->exits);
-		label = bc_vec_item(&p->func->labels, ip->idx);
-		dbg_lex("%s:%d rewriting label: %d -> %d", __func__, __LINE__, *label, p->func->code.len);
-		*label = p->func->code.len;
+	ip.idx = p->func->labels.len;
+	ip.func = ip.len = 0;
 
-		bc_vec_pop(&p->exits);
-		bc_parse_pop_block_flag(p);
-	}
-	else if (BC_PARSE_FUNC_INNER(p)) {
-		bc_parse_push(p, BC_INST_RET0);
-		bc_parse_updateFunc(p, BC_PROG_MAIN);
-		bc_parse_pop_block_flag(p);
-	}
-	else {
-		BcInstPtr *ip = bc_vec_top(&p->exits);
-		size_t *label = bc_vec_top(&p->conds);
+	dbg_lex("%s:%d after if() body: BC_INST_JUMP to %d", __func__, __LINE__, ip.idx);
+	bc_parse_push(p, BC_INST_JUMP);
+	bc_parse_pushIndex(p, ip.idx);
 
-		dbg_lex("%s:%d BC_INST_JUMP to %d", __func__, __LINE__, *label);
-		bc_parse_push(p, BC_INST_JUMP);
-		bc_parse_pushIndex(p, *label);
+	dbg_lex("%s:%d calling bc_parse_noElse()", __func__, __LINE__);
+	bc_parse_noElse(p);
 
-		label = bc_vec_item(&p->func->labels, ip->idx);
-		dbg_lex("%s:%d rewriting label: %d -> %d", __func__, __LINE__, *label, p->func->code.len);
-		*label = p->func->code.len;
+	bc_vec_push(&p->exits, &ip);
+	bc_vec_push(&p->func->labels, &ip.idx);
 
-		bc_vec_pop(&p->exits);
-		bc_vec_pop(&p->conds);
-		bc_parse_pop_block_flag(p);
-	}
+	s = zbc_parse_stmt(p);
+	if (s) RETURN_STATUS(s);
 
+	dbg_lex_done("%s:%d done", __func__, __LINE__);
 	RETURN_STATUS(s);
 }
 #if ERRORS_ARE_FATAL
-# define zbc_parse_endBody(...) (zbc_parse_endBody(__VA_ARGS__), BC_STATUS_SUCCESS)
+# define zbc_parse_else(...) (zbc_parse_else(__VA_ARGS__), BC_STATUS_SUCCESS)
 #endif
 
-static void bc_parse_noElse(BcParse *p)
-{
-	BcInstPtr *ip;
-	size_t *label;
-	uint8_t *flag_ptr = BC_PARSE_TOP_FLAG_PTR(p);
-
-	dbg_lex("%s:%d clearing BC_PARSE_FLAG_IF_END bit", __func__, __LINE__);
-	*flag_ptr = (*flag_ptr & ~(BC_PARSE_FLAG_IF_END));
-
-	ip = bc_vec_top(&p->exits);
-	label = bc_vec_item(&p->func->labels, ip->idx);
-	dbg_lex("%s:%d rewriting label: %d -> %d", __func__, __LINE__, *label, p->func->code.len);
-	*label = p->func->code.len;
-
-	bc_vec_pop(&p->exits);
-}
-
 static BC_STATUS zbc_parse_if(BcParse *p)
 {
 	BcStatus s;
 	BcInstPtr ip;
+	BcInstPtr *ipp;
+	size_t *label;
 
 	dbg_lex_enter("%s:%d entered", __func__, __LINE__);
 	s = zbc_lex_next(&p->l);
@@ -4164,60 +4151,50 @@ static BC_STATUS zbc_parse_if(BcParse *p)
 	if (s) RETURN_STATUS(s);
 	s = zbc_parse_expr(p, BC_PARSE_REL, bc_parse_next_rel);
 	if (s) RETURN_STATUS(s);
-	if (p->l.t.t != BC_LEX_RPAREN) RETURN_STATUS(bc_error_bad_token());
 
+	if (p->l.t.t != BC_LEX_RPAREN) RETURN_STATUS(bc_error_bad_token());
 	s = zbc_lex_next(&p->l);
 	if (s) RETURN_STATUS(s);
-	bc_parse_push(p, BC_INST_JUMP_ZERO);
 
+	bc_parse_push(p, BC_INST_JUMP_ZERO);
 	ip.idx = p->func->labels.len;
 	ip.func = ip.len = 0;
-
 	bc_parse_pushIndex(p, ip.idx);
+//TODO: can get rid of p->exits stack?
 	bc_vec_push(&p->exits, &ip);
 	bc_vec_push(&p->func->labels, &ip.idx);
-	bc_parse_push_block_flag(p, BC_PARSE_FLAG_IF);
 
-	dbg_lex_done("%s:%d done", __func__, __LINE__);
-	RETURN_STATUS(BC_STATUS_SUCCESS);
-}
-#if ERRORS_ARE_FATAL
-# define zbc_parse_if(...) (zbc_parse_if(__VA_ARGS__), BC_STATUS_SUCCESS)
-#endif
-
-#undef zbc_parse_else
-static BC_STATUS zbc_parse_else(BcParse *p)
-{
-	BcInstPtr ip;
-
-	dbg_lex_enter("%s:%d entered", __func__, __LINE__);
-	if (!BC_PARSE_IF_END(p)) RETURN_STATUS(bc_error_bad_token());
-
-	ip.idx = p->func->labels.len;
-	ip.func = ip.len = 0;
-
-	dbg_lex("%s:%d after if() body: BC_INST_JUMP to %d", __func__, __LINE__, ip.idx);
-	bc_parse_push(p, BC_INST_JUMP);
-	bc_parse_pushIndex(p, ip.idx);
+	s = zbc_parse_stmt(p);
+	if (s) RETURN_STATUS(s);
+	dbg_lex("%s:%d in if after stmt: p->l.t.t:%d", __func__, __LINE__, p->l.t.t);
+	if (p->l.t.t == BC_LEX_KEY_ELSE) {
+		s = zbc_lex_next(&p->l);
+		if (s) RETURN_STATUS(s);
+		dbg_lex("%s:%d calling zbc_parse_else(), p->l.t.t:%d", __func__, __LINE__, p->l.t.t);
+		s = zbc_parse_else(p);
+	}
 
-	dbg_lex("%s:%d calling bc_parse_noElse()", __func__, __LINE__);
-	bc_parse_noElse(p);
+	ipp = bc_vec_top(&p->exits);
+	label = bc_vec_item(&p->func->labels, ipp->idx);
+	dbg_lex("%s:%d rewriting label: %d -> %d", __func__, __LINE__, *label, p->func->code.len);
+	*label = p->func->code.len;
 
-	bc_vec_push(&p->exits, &ip);
-	bc_vec_push(&p->func->labels, &ip.idx);
-	bc_parse_push_block_flag(p, BC_PARSE_FLAG_ELSE);
+	bc_vec_pop(&p->exits);
 
 	dbg_lex_done("%s:%d done", __func__, __LINE__);
-	RETURN_STATUS(zbc_lex_next(&p->l));
+	RETURN_STATUS(s);
 }
 #if ERRORS_ARE_FATAL
-# define zbc_parse_else(...) (zbc_parse_else(__VA_ARGS__), BC_STATUS_SUCCESS)
+# define zbc_parse_if(...) (zbc_parse_if(__VA_ARGS__), BC_STATUS_SUCCESS)
 #endif
 
 static BC_STATUS zbc_parse_while(BcParse *p)
 {
 	BcStatus s;
 	BcInstPtr ip;
+	BcInstPtr *ipp;
+	size_t *label;
+	size_t n;
 
 	s = zbc_lex_next(&p->l);
 	if (s) RETURN_STATUS(s);
@@ -4245,9 +4222,29 @@ static BC_STATUS zbc_parse_while(BcParse *p)
 
 	bc_parse_push(p, BC_INST_JUMP_ZERO);
 	bc_parse_pushIndex(p, ip.idx);
-	bc_parse_push_block_flag(p, BC_PARSE_FLAG_LOOP | BC_PARSE_FLAG_LOOP_INNER);
 
-	RETURN_STATUS(BC_STATUS_SUCCESS);
+	s = zbc_parse_stmt(p);
+	if (s) RETURN_STATUS(s);
+
+	n = *((size_t *) bc_vec_top(&p->conds));
+	bc_parse_push(p, BC_INST_JUMP);
+	bc_parse_pushIndex(p, n);
+
+	ipp = bc_vec_top(&p->exits);
+	label = bc_vec_top(&p->conds);
+
+	dbg_lex("%s:%d BC_INST_JUMP to %d", __func__, __LINE__, *label);
+	bc_parse_push(p, BC_INST_JUMP);
+	bc_parse_pushIndex(p, *label);
+
+	label = bc_vec_item(&p->func->labels, ipp->idx);
+	dbg_lex("%s:%d rewriting label: %d -> %d", __func__, __LINE__, *label, p->func->code.len);
+	*label = p->func->code.len;
+
+	bc_vec_pop(&p->exits);
+	bc_vec_pop(&p->conds);
+
+	RETURN_STATUS(s);
 }
 #if ERRORS_ARE_FATAL
 # define zbc_parse_while(...) (zbc_parse_while(__VA_ARGS__), BC_STATUS_SUCCESS)
@@ -4257,7 +4254,10 @@ static BC_STATUS zbc_parse_for(BcParse *p)
 {
 	BcStatus s;
 	BcInstPtr ip;
+	BcInstPtr *ipp;
+	size_t *label;
 	size_t cond_idx, exit_idx, body_idx, update_idx;
+	size_t n;
 
 	dbg_lex("%s:%d p->l.t.t:%d", __func__, __LINE__, p->l.t.t);
 	s = zbc_lex_next(&p->l);
@@ -4324,7 +4324,28 @@ static BC_STATUS zbc_parse_for(BcParse *p)
 	bc_vec_push(&p->func->labels, &ip.idx);
 	s = zbc_lex_next(&p->l);
 	if (s) RETURN_STATUS(s);
-	bc_parse_push_block_flag(p, BC_PARSE_FLAG_LOOP | BC_PARSE_FLAG_LOOP_INNER);
+
+	s = zbc_parse_stmt(p);
+	if (s) RETURN_STATUS(s);
+
+	n = *((size_t *) bc_vec_top(&p->conds));
+	bc_parse_push(p, BC_INST_JUMP);
+	bc_parse_pushIndex(p, n);
+
+	ipp = bc_vec_top(&p->exits);
+	label = bc_vec_top(&p->conds);
+
+//TODO: commonalize?
+	dbg_lex("%s:%d BC_INST_JUMP to %d", __func__, __LINE__, *label);
+	bc_parse_push(p, BC_INST_JUMP);
+	bc_parse_pushIndex(p, *label);
+
+	label = bc_vec_item(&p->func->labels, ipp->idx);
+	dbg_lex("%s:%d rewriting label: %d -> %d", __func__, __LINE__, *label, p->func->code.len);
+	*label = p->func->code.len;
+
+	bc_vec_pop(&p->exits);
+	bc_vec_pop(&p->conds);
 
 	RETURN_STATUS(BC_STATUS_SUCCESS);
 }
@@ -4332,14 +4353,12 @@ static BC_STATUS zbc_parse_for(BcParse *p)
 # define zbc_parse_for(...) (zbc_parse_for(__VA_ARGS__), BC_STATUS_SUCCESS)
 #endif
 
-static BC_STATUS zbc_parse_loopExit(BcParse *p, BcLexType type)
+static BC_STATUS zbc_parse_break_or_continue(BcParse *p, BcLexType type)
 {
 	BcStatus s;
 	size_t i;
 	BcInstPtr *ip;
 
-	if (!BC_PARSE_LOOP(p)) RETURN_STATUS(bc_error_bad_token());
-
 	if (type == BC_LEX_KEY_BREAK) {
 		if (p->exits.len == 0) RETURN_STATUS(bc_error_bad_token());
 
@@ -4368,14 +4387,13 @@ static BC_STATUS zbc_parse_loopExit(BcParse *p, BcLexType type)
 	RETURN_STATUS(zbc_lex_next(&p->l));
 }
 #if ERRORS_ARE_FATAL
-# define zbc_parse_loopExit(...) (zbc_parse_loopExit(__VA_ARGS__), BC_STATUS_SUCCESS)
+# define zbc_parse_break_or_continue(...) (zbc_parse_break_or_continue(__VA_ARGS__), BC_STATUS_SUCCESS)
 #endif
 
 static BC_STATUS zbc_parse_func(BcParse *p)
 {
 	BcStatus s;
 	bool var, comma = false;
-	uint8_t flags;
 	char *name;
 
 	s = zbc_lex_next(&p->l);
@@ -4430,15 +4448,18 @@ static BC_STATUS zbc_parse_func(BcParse *p)
 
 	if (comma) RETURN_STATUS(bc_error("bad function definition"));
 
-	flags = BC_PARSE_FLAG_FUNC | BC_PARSE_FLAG_FUNC_INNER | BC_PARSE_FLAG_BODY;
-	bc_parse_push_block_flag(p, flags);
-
 	s = zbc_lex_next(&p->l);
 	if (s) RETURN_STATUS(s);
 
 	if (p->l.t.t != BC_LEX_LBRACE)
 		s = bc_POSIX_requires("the left brace be on the same line as the function header");
 
+	s = zbc_parse_stmt_possibly_auto(p, true);
+	if (s) RETURN_STATUS(s);
+
+	bc_parse_push(p, BC_INST_RET0);
+	bc_parse_updateFunc(p, BC_PROG_MAIN);
+
 	RETURN_STATUS(s);
 
 err:
@@ -4455,12 +4476,11 @@ static BC_STATUS zbc_parse_auto(BcParse *p)
 	bool comma, var, one;
 	char *name;
 
-	if (!p->auto_part) RETURN_STATUS(bc_error_bad_token());
-
+	dbg_lex_enter("%s:%d entered", __func__, __LINE__);
 	s = zbc_lex_next(&p->l);
 	if (s) RETURN_STATUS(s);
 
-	p->auto_part = comma = false;
+	comma = false;
 	one = p->l.t.t == BC_LEX_NAME;
 
 	while (p->l.t.t == BC_LEX_NAME) {
@@ -4498,91 +4518,53 @@ static BC_STATUS zbc_parse_auto(BcParse *p)
 	if (p->l.t.t != BC_LEX_NLINE && p->l.t.t != BC_LEX_SCOLON)
 		RETURN_STATUS(bc_error_bad_token());
 
+	dbg_lex_done("%s:%d done", __func__, __LINE__);
 	RETURN_STATUS(zbc_lex_next(&p->l));
 
 err:
 	free(name);
+	dbg_lex_done("%s:%d done (ERROR)", __func__, __LINE__);
 	RETURN_STATUS(s);
 }
 #if ERRORS_ARE_FATAL
 # define zbc_parse_auto(...) (zbc_parse_auto(__VA_ARGS__), BC_STATUS_SUCCESS)
 #endif
 
-static BC_STATUS zbc_parse_body(BcParse *p, bool brace)
+#undef zbc_parse_stmt_possibly_auto
+static BC_STATUS zbc_parse_stmt_possibly_auto(BcParse *p, bool auto_allowed)
 {
 	BcStatus s = BC_STATUS_SUCCESS;
-	uint8_t *flag_ptr = BC_PARSE_TOP_FLAG_PTR(p);
-
-	dbg_lex_enter("%s:%d entered", __func__, __LINE__);
-	*flag_ptr &= ~(BC_PARSE_FLAG_BODY);
 
-	if (*flag_ptr & BC_PARSE_FLAG_FUNC_INNER) {
-		dbg_lex("%s:%d BC_PARSE_FLAG_FUNC_INNER", __func__, __LINE__);
-		if (!brace) RETURN_STATUS(bc_error_bad_token());
-
-		p->auto_part = p->l.t.t != BC_LEX_KEY_AUTO;
-
-		if (!p->auto_part) {
-			s = zbc_parse_auto(p);
-			if (s) RETURN_STATUS(s);
-		}
+	dbg_lex_enter("%s:%d entered, p->l.t.t:%d", __func__, __LINE__, p->l.t.t);
 
-		if (p->l.t.t == BC_LEX_NLINE) s = zbc_lex_next(&p->l);
+	if (p->l.t.t == BC_LEX_NLINE) {
+		dbg_lex_done("%s:%d done (seen BC_LEX_NLINE)", __func__, __LINE__);
+		RETURN_STATUS(zbc_lex_next(&p->l));
 	}
-	else {
-		dbg_lex("%s:%d !BC_PARSE_FLAG_FUNC_INNER", __func__, __LINE__);
-		s = zbc_parse_stmt(p);
-		if (!s && !brace && !BC_PARSE_BODY(p)) s = zbc_parse_endBody(p);
+	if (p->l.t.t == BC_LEX_SCOLON) {
+		dbg_lex_done("%s:%d done (seen BC_LEX_SCOLON)", __func__, __LINE__);
+		RETURN_STATUS(zbc_lex_next(&p->l));
 	}
 
-	dbg_lex_done("%s:%d done", __func__, __LINE__);
-	RETURN_STATUS(s);
-}
-#if ERRORS_ARE_FATAL
-# define zbc_parse_body(...) (zbc_parse_body(__VA_ARGS__), BC_STATUS_SUCCESS)
-#endif
-
-#undef zbc_parse_stmt
-static BC_STATUS zbc_parse_stmt(BcParse *p)
-{
-	BcStatus s = BC_STATUS_SUCCESS;
-
-	dbg_lex_enter("%s:%d entered, p->l.t.t:%d", __func__, __LINE__, p->l.t.t);
-	switch (p->l.t.t) {
-		case BC_LEX_NLINE:
-			dbg_lex_done("%s:%d done (seen BC_LEX_NLINE)", __func__, __LINE__);
-			RETURN_STATUS(zbc_lex_next(&p->l));
-
-		case BC_LEX_KEY_ELSE:
-			dbg_lex("%s:%d BC_LEX_KEY_ELSE:", __func__, __LINE__);
-			p->auto_part = false;
-			break;
-
-		case BC_LEX_LBRACE:
-			dbg_lex("%s:%d BC_LEX_LBRACE:", __func__, __LINE__);
-			if (!BC_PARSE_BODY(p)) RETURN_STATUS(bc_error_bad_token());
-			++p->nbraces;
+	if (p->l.t.t == BC_LEX_LBRACE) {
+		dbg_lex("%s:%d BC_LEX_LBRACE: (auto_allowed:%d)", __func__, __LINE__, auto_allowed);
+		do {
 			s = zbc_lex_next(&p->l);
 			if (s) RETURN_STATUS(s);
-			dbg_lex_done("%s:%d done (returning zbc_parse_body())", __func__, __LINE__);
-			RETURN_STATUS(zbc_parse_body(p, true));
-
-		case BC_LEX_KEY_AUTO:
-			dbg_lex("%s:%d BC_LEX_KEY_AUTO:", __func__, __LINE__);
-			RETURN_STATUS(zbc_parse_auto(p));
-
-		default:
-			p->auto_part = false;
-			if (BC_PARSE_IF_END(p)) {
-				bc_parse_noElse(p);
-				dbg_lex_done("%s:%d done (BC_PARSE_IF_END is true)", __func__, __LINE__);
-				RETURN_STATUS(BC_STATUS_SUCCESS);
-			}
-			if (BC_PARSE_BODY(p)) {
-				dbg_lex_done("%s:%d done (returning zbc_parse_body())", __func__, __LINE__);
-				RETURN_STATUS(zbc_parse_body(p, false));
-			}
-			break;
+		} while (p->l.t.t == BC_LEX_NLINE);
+		if (auto_allowed && p->l.t.t == BC_LEX_KEY_AUTO) {
+			dbg_lex("%s:%d calling zbc_parse_auto()", __func__, __LINE__);
+			s = zbc_parse_auto(p);
+			if (s) RETURN_STATUS(s);
+		}
+		while (p->l.t.t != BC_LEX_RBRACE) {
+			dbg_lex("%s:%d block parsing loop", __func__, __LINE__);
+			s = zbc_parse_stmt(p);
+			if (s) RETURN_STATUS(s);
+		}
+		s = zbc_lex_next(&p->l);
+		dbg_lex_done("%s:%d done (seen BC_LEX_RBRACE)", __func__, __LINE__);
+		RETURN_STATUS(s);
 	}
 
 	dbg_lex("%s:%d p->l.t.t:%d", __func__, __LINE__, p->l.t.t);
@@ -4603,26 +4585,12 @@ static BC_STATUS zbc_parse_stmt(BcParse *p)
 		case BC_LEX_KEY_SQRT:
 			s = zbc_parse_expr(p, BC_PARSE_PRINT, bc_parse_next_expr);
 			break;
-		case BC_LEX_KEY_ELSE:
-			s = zbc_parse_else(p);
-			break;
-		case BC_LEX_SCOLON:
-			while (!s && p->l.t.t == BC_LEX_SCOLON) s = zbc_lex_next(&p->l);
-			break;
-		case BC_LEX_RBRACE:
-			if (p->nbraces == 0)
-				RETURN_STATUS(bc_error_bad_token());
-			--p->nbraces;
-			s = zbc_lex_next(&p->l);
-			if (!s)
-				s = zbc_parse_endBody(p);
-			break;
 		case BC_LEX_STR:
 			s = zbc_parse_string(p, BC_INST_PRINT_STR);
 			break;
 		case BC_LEX_KEY_BREAK:
 		case BC_LEX_KEY_CONTINUE:
-			s = zbc_parse_loopExit(p, p->l.t.t);
+			s = zbc_parse_break_or_continue(p, p->l.t.t);
 			break;
 		case BC_LEX_KEY_FOR:
 			s = zbc_parse_for(p);
@@ -4637,8 +4605,6 @@ static BC_STATUS zbc_parse_stmt(BcParse *p)
 		case BC_LEX_KEY_LIMITS:
 			// "limits" is a compile-time command,
 			// the output is produced at _parse time_.
-			s = zbc_lex_next(&p->l);
-			if (s) RETURN_STATUS(s);
 			printf(
 				"BC_BASE_MAX     = "BC_MAX_OBASE_STR "\n"
 				"BC_DIM_MAX      = "BC_MAX_DIM_STR   "\n"
@@ -4649,6 +4615,7 @@ static BC_STATUS zbc_parse_stmt(BcParse *p)
 				"MAX Exponent    = "BC_MAX_EXP_STR   "\n"
 				"Number of vars  = "BC_MAX_VARS_STR  "\n"
 			);
+			s = zbc_lex_next(&p->l);
 			break;
 		case BC_LEX_KEY_PRINT:
 			s = zbc_parse_print(p);
@@ -4669,11 +4636,16 @@ static BC_STATUS zbc_parse_stmt(BcParse *p)
 			break;
 	}
 
+	if (s || G_interrupt) {
+		bc_parse_reset(p);
+		s = BC_STATUS_FAILURE;
+	}
+
 	dbg_lex_done("%s:%d done", __func__, __LINE__);
 	RETURN_STATUS(s);
 }
 #if ERRORS_ARE_FATAL
-# define zbc_parse_stmt(...) (zbc_parse_stmt(__VA_ARGS__), BC_STATUS_SUCCESS)
+# define zbc_parse_stmt_possibly_auto(...) (zbc_parse_stmt_possibly_auto(__VA_ARGS__), BC_STATUS_SUCCESS)
 #endif
 
 static BC_STATUS zbc_parse_stmt_or_funcdef(BcParse *p)
@@ -4682,22 +4654,15 @@ static BC_STATUS zbc_parse_stmt_or_funcdef(BcParse *p)
 
 	dbg_lex_enter("%s:%d entered", __func__, __LINE__);
 	if (p->l.t.t == BC_LEX_EOF)
-		s = BC_PARSE_FLAG_STACK_EMPTY(p) ? bc_error("end of file") : bc_error("block end could not be found");
+		s = bc_error("end of file");
 	else if (p->l.t.t == BC_LEX_KEY_DEFINE) {
 		dbg_lex("%s:%d p->l.t.t:BC_LEX_KEY_DEFINE", __func__, __LINE__);
-		if (!BC_PARSE_CAN_EXEC(p))
-			RETURN_STATUS(bc_error_bad_token());
 		s = zbc_parse_func(p);
 	} else {
 		dbg_lex("%s:%d p->l.t.t:%d (not BC_LEX_KEY_DEFINE)", __func__, __LINE__, p->l.t.t);
 		s = zbc_parse_stmt(p);
 	}
 
-	if (s || G_interrupt) {
-		bc_parse_reset(p);
-		s = BC_STATUS_FAILURE;
-	}
-
 	dbg_lex_done("%s:%d done", __func__, __LINE__);
 	RETURN_STATUS(s);
 }
@@ -4940,6 +4905,7 @@ static BcStatus bc_parse_expr_empty_ok(BcParse *p, uint8_t flags, BcParseNext ne
 	if (prev == BC_INST_BOOL_NOT || nexprs != 1)
 		return bc_error_bad_expression();
 
+//TODO: why is this needed at all?
 	// next is BcParseNext, byte array of up to 4 BC_LEX's, packed into 32-bit word
 	for (;;) {
 		if (t == (next & 0x7f))
@@ -4948,7 +4914,8 @@ static BcStatus bc_parse_expr_empty_ok(BcParse *p, uint8_t flags, BcParseNext ne
 			break;
 		next >>= 8;
 	}
-	return bc_error_bad_expression();
+	if (t != BC_LEX_KEY_ELSE)
+		return bc_error_bad_expression();
  ok:
 
 	if (!(flags & BC_PARSE_REL) && nrelops) {
@@ -6766,6 +6733,7 @@ static BC_STATUS zbc_program_exec(void)
 				s = zbc_program_incdec(inst);
 				break;
 			case BC_INST_HALT:
+				dbg_exec("BC_INST_HALT:");
 				QUIT_OR_RETURN_TO_MAIN;
 				break;
 			case BC_INST_RET:
@@ -6939,6 +6907,7 @@ static BC_STATUS zbc_program_exec(void)
 				break;
 			}
 			case BC_INST_QUIT:
+				dbg_exec("BC_INST_NEG:");
 				if (G.prog.stack.len <= 2)
 					QUIT_OR_RETURN_TO_MAIN;
 				bc_vec_npop(&G.prog.stack, 2);
@@ -6994,14 +6963,12 @@ static BC_STATUS zbc_vm_process(const char *text)
 		dbg_lex("%s:%d G.prs.l.t.t:%d", __func__, __LINE__, G.prs.l.t.t);
 		ERROR_RETURN(s =) zcommon_parse(&G.prs);
 		if (s) RETURN_STATUS(s);
-	}
-	dbg_lex("%s:%d G.prs.l.t.t:BC_LEX_EOF", __func__, __LINE__);
-
-	if (BC_PARSE_CAN_EXEC(&G.prs)) {
 		s = zbc_program_exec();
-		fflush_and_check();
-		if (s)
+		if (s) {
 			bc_program_reset();
+			break;
+		}
+		fflush_and_check();
 	}
 
 	dbg_lex_done("%s:%d done", __func__, __LINE__);
@@ -7049,91 +7016,12 @@ err:
 static BC_STATUS zbc_vm_stdin(void)
 {
 	BcStatus s;
-	BcVec buffer;
-	size_t str;
-	bool comment;
 
 	//G.prog.file = NULL; - already is
 	bc_lex_file(&G.prs.l);
 
-	bc_char_vec_init(&buffer);
-
-	// This loop is complex because the vm tries not to send any lines that end
-	// with a backslash to the parser. The reason for that is because the parser
-	// treats a backslash+newline combo as whitespace, per the bc spec. In that
-	// case, and for strings and comments, the parser will expect more stuff.
-	s = BC_STATUS_SUCCESS;
-	comment = false;
-	str = 0;
-	for (;;) {
-		size_t prevlen = buffer.len;
-		char *string;
-
-		bc_read_line(&buffer);
-		// No more input means EOF
-		if (buffer.len <= prevlen + 1) // (we expect +1 for NUL byte)
-			break;
-
-		string = buffer.v + prevlen;
-		while (*string) {
-			char c = *string;
-			if (string == buffer.v || string[-1] != '\\') {
-				if (IS_BC)
-					str ^= (c == '"');
-				else {
-					if (c == ']')
-						str -= 1;
-					else if (c == '[')
-						str += 1;
-				}
-			}
-			string++;
-			if (c == '/' && *string == '*') {
-				comment = true;
-				string++;
-				continue;
-			}
-			if (c == '*' && *string == '/') {
-				comment = false;
-				string++;
-			}
-		}
-		if (str || comment) {
-			buffer.len--; // backstep over the trailing NUL byte
-			continue;
-		}
-
-		// Check for backslash+newline.
-		// we do not check that last char is '\n' -
-		// if it is not, then it's EOF, and looping back
-		// to bc_read_line() will detect it:
-		string -= 2;
-		if (string >= buffer.v && *string == '\\') {
-			buffer.len--;
-			continue;
-		}
-
-		s = zbc_vm_process(buffer.v);
-		if (s) {
-			if (ENABLE_FEATURE_CLEAN_UP && !G_ttyin) {
-				// Debug config, non-interactive mode:
-				// return all the way back to main.
-				// Non-debug builds do not come here, they exit.
-				break;
-			}
-		}
-
-		bc_vec_pop_all(&buffer);
-	}
-
-	if (str) {
-		s = bc_error("string end could not be found");
-	}
-	else if (comment) {
-		s = bc_error("comment end could not be found");
-	}
-
-	bc_vec_free(&buffer);
+	G.use_stdin = 1;
+	s = zbc_vm_process("");
 	RETURN_STATUS(s);
 }
 #if ERRORS_ARE_FATAL
@@ -7412,9 +7300,6 @@ static BC_STATUS zbc_vm_exec(void)
 	if (IS_BC || (option_mask32 & BC_FLAG_I))
 		s = zbc_vm_stdin();
 
-	if (!s && !BC_PARSE_CAN_EXEC(&G.prs))
-		s = zbc_vm_process("");
-
 	RETURN_STATUS(s);
 }
 #if ERRORS_ARE_FATAL
@@ -7443,6 +7328,7 @@ static void bc_program_free(void)
 	bc_num_free(&G.prog.last);
 	bc_num_free(&G.prog.zero);
 	bc_num_free(&G.prog.one);
+	bc_vec_free(&G.stdin_buffer);
 }
 
 static void bc_vm_free(void)
@@ -7506,6 +7392,8 @@ static void bc_program_init(void)
 	bc_vec_init(&G.prog.results, sizeof(BcResult), bc_result_free);
 	bc_vec_init(&G.prog.stack, sizeof(BcInstPtr), NULL);
 	bc_vec_push(&G.prog.stack, &ip);
+
+	bc_char_vec_init(&G.stdin_buffer);
 }
 
 static int bc_vm_init(const char *env_len)
@@ -7562,6 +7450,7 @@ static BcStatus bc_vm_run(void)
 # endif
 	FREE_G();
 #endif
+	dbg_exec("exiting with exitcode %d", st);
 	return st;
 }