Added `continue` keyword to Lua 5.4 [code review requested].
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- Subject: Added `continue` keyword to Lua 5.4 [code review requested].
- From: David Sicilia <dpsicilia@...>
- Date: 2023年3月17日 10:37:36 -0400
Hi all,
I have patched Lua 5.4.5 to add the `continue` keyword to the for loop, while loop, and repeat loop, and I've attached the patch file and some test code. Use it like so:
for i = 1, 10 do
if i % 2 == 0 then continue end
print( i )
end
This should really help to reduce unnecessary if-statement nesting inside loops.
Since this is my first time patching Lua, can someone help to review my patch?
It was surprisingly easy since the `continue` keyword can be implemented entirely at the parser level as an implicit `goto`, similar to `break`. The only part I wasn't sure of was the part in the test_then_block function -- not sure what the purpose of that is, as my tests seem to work whether I update it or not.
Thanks in advance,
David
diff --git a/llex.c b/llex.c
index b0dc0acc..f96a0239 100644
--- a/llex.c
+++ b/llex.c
@@ -38,7 +38,7 @@
/* ORDER RESERVED */
static const char *const luaX_tokens [] = {
- "and", "break", "do", "else", "elseif",
+ "and", "break", "continue", "do", "else", "elseif",
"end", "false", "for", "function", "goto", "if",
"in", "local", "nil", "not", "or", "repeat",
"return", "then", "true", "until", "while",
diff --git a/llex.h b/llex.h
index 389d2f86..bb55dafe 100644
--- a/llex.h
+++ b/llex.h
@@ -31,7 +31,7 @@
*/
enum RESERVED {
/* terminal symbols denoted by reserved words */
- TK_AND = FIRST_RESERVED, TK_BREAK,
+ TK_AND = FIRST_RESERVED, TK_BREAK, TK_CONTINUE,
TK_DO, TK_ELSE, TK_ELSEIF, TK_END, TK_FALSE, TK_FOR, TK_FUNCTION,
TK_GOTO, TK_IF, TK_IN, TK_LOCAL, TK_NIL, TK_NOT, TK_OR, TK_REPEAT,
TK_RETURN, TK_THEN, TK_TRUE, TK_UNTIL, TK_WHILE,
diff --git a/lparser.c b/lparser.c
index 24668c24..773dc070 100644
--- a/lparser.c
+++ b/lparser.c
@@ -661,6 +661,10 @@ static l_noret undefgoto (LexState *ls, Labeldesc *gt) {
msg = "break outside loop at line %d";
msg = luaO_pushfstring(ls->L, msg, gt->line);
}
+ else if (eqstr(gt->name, luaS_newliteral(ls->L, "continue"))) {
+ msg = "continue outside loop at line %d";
+ msg = luaO_pushfstring(ls->L, msg, gt->line);
+ }
else {
msg = "no visible label '%s' for <goto> at line %d";
msg = luaO_pushfstring(ls->L, msg, getstr(gt->name), gt->line);
@@ -669,6 +673,12 @@ static l_noret undefgoto (LexState *ls, Labeldesc *gt) {
}
+static void endloopblock (FuncState *fs) {
+ LexState *ls = fs->ls;
+ createlabel(ls, luaS_newliteral(ls->L, "continue"), 0, 0);
+}
+
+
static void leaveblock (FuncState *fs) {
BlockCnt *bl = fs->bl;
LexState *ls = fs->ls;
@@ -1442,6 +1452,16 @@ static void breakstat (LexState *ls) {
}
+/*
+** Continue statement. Semantically equivalent to "goto continue".
+*/
+static void contstat (LexState *ls) {
+ int line = ls->linenumber;
+ luaX_next(ls); /* skip continue */
+ newgotoentry(ls, luaS_newliteral(ls->L, "continue"), line, luaK_jump(ls->fs));
+}
+
+
/*
** Check whether there is already a label with the given 'name'.
*/
@@ -1477,6 +1497,7 @@ static void whilestat (LexState *ls, int line) {
enterblock(fs, &bl, 1);
checknext(ls, TK_DO);
block(ls);
+ endloopblock(fs); /* inside loop scope ('continue' jumps to this point) */
luaK_jumpto(fs, whileinit);
check_match(ls, TK_END, TK_WHILE, line);
leaveblock(fs);
@@ -1494,6 +1515,7 @@ static void repeatstat (LexState *ls, int line) {
enterblock(fs, &bl2, 0); /* scope block */
luaX_next(ls); /* skip REPEAT */
statlist(ls);
+ endloopblock(fs); /* inside loop scope ('continue' jumps to this point) */
check_match(ls, TK_UNTIL, TK_REPEAT, line);
condexit = cond(ls); /* read condition (inside scope block) */
leaveblock(fs); /* finish scope */
@@ -1554,6 +1576,7 @@ static void forbody (LexState *ls, int base, int line, int nvars, int isgen) {
adjustlocalvars(ls, nvars);
luaK_reserveregs(fs, nvars);
block(ls);
+ endloopblock(fs); /* inside loop scope ('continue' jumps to this point) */
leaveblock(fs); /* end of scope for declared variables */
fixforjump(fs, prep, luaK_getlabel(fs), 0);
if (isgen) { /* generic for? */
@@ -1644,12 +1667,16 @@ static void test_then_block (LexState *ls, int *escapelist) {
luaX_next(ls); /* skip IF or ELSEIF */
expr(ls, &v); /* read condition */
checknext(ls, TK_THEN);
- if (ls->t.token == TK_BREAK) { /* 'if x then break' ? */
+ if (ls->t.token == TK_BREAK ||
+ ls->t.token == TK_CONTINUE) { /* 'if x then (break | continue)' ? */
int line = ls->linenumber;
luaK_goiffalse(ls->fs, &v); /* will jump if condition is true */
luaX_next(ls); /* skip 'break' */
enterblock(fs, &bl, 0); /* must enter block before 'goto' */
- newgotoentry(ls, luaS_newliteral(ls->L, "break"), line, v.t);
+ if (ls->t.token == TK_BREAK)
+ newgotoentry(ls, luaS_newliteral(ls->L, "break"), line, v.t);
+ else /* ls->t.token == TK_CONTINUE */
+ newgotoentry(ls, luaS_newliteral(ls->L, "continue"), line, v.t);
while (testnext(ls, ';')) {} /* skip semicolons */
if (block_follow(ls, 0)) { /* jump is the entire block? */
leaveblock(fs);
@@ -1658,7 +1685,7 @@ static void test_then_block (LexState *ls, int *escapelist) {
else /* must skip over 'then' part if condition is false */
jf = luaK_jump(fs);
}
- else { /* regular case (not a break) */
+ else { /* regular case (not a break or continue) */
luaK_goiftrue(ls->fs, &v); /* skip over block if condition is false */
enterblock(fs, &bl, 0);
jf = v.f;
@@ -1898,6 +1925,10 @@ static void statement (LexState *ls) {
breakstat(ls);
break;
}
+ case TK_CONTINUE: { /* stat -> contstat */
+ contstat(ls);
+ break;
+ }
case TK_GOTO: { /* stat -> 'goto' NAME */
luaX_next(ls); /* skip 'goto' */
gotostat(ls);
lst = { 'one', 'two', 'three', 'four', 'five', 'six' }
local function closable()
return setmetatable( {}, {
__close = function()
print( '', '==> I was closed.' )
end
} )
end
print( '-------- repeat loop -----------' )
local idx = 1
repeat
local word = lst[idx]
idx = idx + 1
local _<close> = closable()
if word:sub( 1, 1 ) == 't' then continue end
print( idx-1, word )
until idx > 6
print( '-------- while loop -----------' )
local idx = 1
while idx <= 6 do
local word = lst[idx]
idx = idx + 1
local _<close> = closable()
if word:sub( 1, 1 ) == 't' then continue end
print( idx-1, word )
end
print( '-------- for loop -----------' )
for idx, word in ipairs( lst ) do
local _<close> = closable()
if word:sub( 1, 1 ) == 't' then continue end
print( idx, word )
end
print( '-------- multiple statements -----------' )
for idx, word in ipairs( lst ) do
local _<close> = closable()
if word:sub( 1, 1 ) == 't' then
print( '', '==> I am continuing.' )
continue
end
print( idx, word )
end