继续：
int Perl_yyparse (pTHX_ int gramtype){
register yy_parser *parser;
register yy_stack_frame *ps;
----从这两句话，我们看出，有两个变量用于parser，也就是说，是一种多层语言。
这种技术，是很常见的。比如，解析一门语言时，进入了另一种状态，比如进入了注释。
往前，我们找到最重要的一句话：
parser->yychar = yylex();
，所有的编译器都是这样的，lex是yacc的一个工具。所以，自然要从yacc中调用lex.
简单来说，编译器，是一种流式的解析器，它一次读入流，完成一个任务。
虽然，有的编译器，如C语言，理论上，是多遍完成解析的，因为有预编译。
但，对于每一次来说，也就是每一种输入来说，只需要解析一次。
这也是编译器的精妙之处。
lex的任务，是一个字符，一个字符地读入，然后驱动内部的状态机。当状态机被激发，则会发给yacc一个token.
前面我解释过了，perl解析器，没有专门编写一个lex文件，而是直接手工编写了一个token. 只是原理，也lex没有差别。
============
歇一会，
的第504行找到：
barestmt: PLUGSTMT
{ $$ = $1; }
| PEG
{
$$ = newOP(OP_NULL,0);
TOKEN_GETMAD($1,$$,'p');
}
。。。
| ';'
{
PL_parser->expect = XSTATE;
$$ = IF_MAD(newOP(OP_NULL, 0), (OP*)NULL);
TOKEN_GETMAD($1,$$,';');
PL_parser->copline = NOLINE;
}
;
========================================
现在，停掉重头再来。
因为关键的东西还都没有找到。
重新写个脚本，最简单的：
前面，打两个回车，然后定义个变量，就可以了。
编译器都是这样写的，从一个个简单的语句解析开始。
然后，在token.c中，找到一句话：
void
Perl_lex_start(pTHX_ SV *line, PerlIO *rsfp, U32 flags)
{
。。。
parser->linestart = SvPVX(parser->linestr);
parser->linestr，是在哪里初始化的呢？
-----------
SvPVX，是从yacc的当前yyval中，得到想要的东西。因为yyval是一个union，所以，要根据需要，得到那个具体的值。
define SvPVX(sv) ((sv)->sv_u.svu_pv)
char *linestart;
-------------------------
重来。
真是难搞。
找到了第一行处。
我一定是错过了许多东西。而且大部分地方，也没看懂。
原来是想拿来直接用perl解析器。
然后加个自定义的东西。
现在来看，太难了。
我再想想其它的办法。
就算是一个记录吧。
找到第一个identify是在这里：
现在，才明白，原来lex和yacc的解析器，语法与perl很象。
找到了赋值语句：
termbinop: term ASSIGNOP term
{ $$ = newASSIGNOP(OPf_STACKED, $1, IVAL($2), $3);
TOKEN_GETMAD($2,$$,'o');
}
在核心的op.c中：
/*
=for apidoc Am|OP *|newASSIGNOP|I32 flags|OP *left|I32 optype|OP *right
Constructs, checks, and returns an assignment op. I<left> and I<right>
supply the parameters of the assignment; they are consumed by this
function and become part of the constructed op tree.
If I<optype> is C<OP_ANDASSIGN>, C<OP_ORASSIGN>, or C<OP_DORASSIGN>, then
a suitable conditional optree is constructed. If I<optype> is the opcode
of a binary operator, such as C<OP_BIT_OR>, then an op is constructed that
performs the binary operation and assigns the result to the left argument.
Either way, if I<optype> is non-zero then I<flags> has no effect.
If I<optype> is zero, then a plain scalar or list assignment is
constructed. Which type of assignment it is is automatically determined.
I<flags> gives the eight bits of C<op_flags>, except that C<OPf_KIDS>
will be set automatically, and, shifted up eight bits, the eight bits
of C<op_private>, except that the bit with value 1 or 2 is automatically
set as required.
=cut
*/
OP *
Perl_newASSIGNOP(pTHX_ I32 flags, OP *left, I32 optype, OP *right)
{
dVAR;
OP *o;
if (optype) {
if (optype == OP_ANDASSIGN || optype == OP_ORASSIGN || optype == OP_DORASSIGN) {
return newLOGOP(optype, 0,
op_lvalue(scalar(left), optype),
newUNOP(OP_SASSIGN, 0, scalar(right)));
}
else {
return newBINOP(optype, OPf_STACKED,
op_lvalue(scalar(left), optype), scalar(right));
}
}
if (is_list_assignment(left)) {
static const char no_list_state[] = "Initialization of state variables"
" in list context currently forbidden";
OP *curop;
bool maybe_common_vars = TRUE;
PL_modcount = 0;
left = op_lvalue(left, OP_AASSIGN);
curop = list(force_list(left));
o = newBINOP(OP_AASSIGN, flags, list(force_list(right)), curop);
o->op_private = (U8)(0 | (flags >> 8));
if ((left->op_type == OP_LIST
|| (left->op_type == OP_NULL && left->op_targ == OP_LIST)))
{
OP* lop = ((LISTOP*)left)->op_first;
maybe_common_vars = FALSE;
while (lop) {
if (lop->op_type == OP_PADSV ||
lop->op_type == OP_PADAV ||
lop->op_type == OP_PADHV ||
lop->op_type == OP_PADANY) {
if (!(lop->op_private & OPpLVAL_INTRO))
maybe_common_vars = TRUE;
if (lop->op_private & OPpPAD_STATE) {
if (left->op_private & OPpLVAL_INTRO) {
/* Each variable in state($a, $b, $c) = ... */
}
else {
/* Each state variable in
(state $a, my $b, our $c, $d, undef) = ... */
}
yyerror(no_list_state);
} else {
/* Each my variable in
(state $a, my $b, our $c, $d, undef) = ... */
}
} else if (lop->op_type == OP_UNDEF ||
lop->op_type == OP_PUSHMARK) {
/* undef may be interesting in
(state $a, undef, state $c) */
} else {
/* Other ops in the list. */
maybe_common_vars = TRUE;
}
lop = lop->op_sibling;
}
}
else if ((left->op_private & OPpLVAL_INTRO)
&& ( left->op_type == OP_PADSV
|| left->op_type == OP_PADAV
|| left->op_type == OP_PADHV
|| left->op_type == OP_PADANY))
{
if (left->op_type == OP_PADSV) maybe_common_vars = FALSE;
if (left->op_private & OPpPAD_STATE) {
/* All single variable list context state assignments, hence
state ($a) = ...
(state $a) = ...
state @a = ...
state (@a) = ...
(state @a) = ...
state %a = ...
state (%a) = ...
(state %a) = ...
*/
yyerror(no_list_state);
}
}
/* PL_generation sorcery:
* an assignment like ($a,$b) = ($c,$d) is easier than
* ($a,$b) = ($c,$a), since there is no need for temporary vars.
* To detect whether there are common vars, the global var
* PL_generation is incremented for each assign op we compile.
* Then, while compiling the assign op, we run through all the
* variables on both sides of the assignment, setting a spare slot
* in each of them to PL_generation. If any of them already have
* that value, we know we've got commonality. We could use a
* single bit marker, but then we'd have to make 2 passes, first
* to clear the flag, then to test and set it. To find somewhere
* to store these values, evil chicanery is done with SvUVX().
*/
if (maybe_common_vars) {
PL_generation++;
if (aassign_common_vars(o))
o->op_private |= OPpASSIGN_COMMON;
LINKLIST(o);
}
if (right && right->op_type == OP_SPLIT && !PL_madskills) {
OP* tmpop = ((LISTOP*)right)->op_first;
if (tmpop && (tmpop->op_type == OP_PUSHRE)) {
PMOP * const pm = (PMOP*)tmpop;
if (left->op_type == OP_RV2AV &&
!(left->op_private & OPpLVAL_INTRO) &&
!(o->op_private & OPpASSIGN_COMMON) )
{
tmpop = ((UNOP*)left)->op_first;
if (tmpop->op_type == OP_GV
#ifdef USE_ITHREADS
&& !pm->op_pmreplrootu.op_pmtargetoff
#else
&& !pm->op_pmreplrootu.op_pmtargetgv
#endif
) {
#ifdef USE_ITHREADS
pm->op_pmreplrootu.op_pmtargetoff
= cPADOPx(tmpop)->op_padix;
cPADOPx(tmpop)->op_padix = 0; /* steal it */
#else
pm->op_pmreplrootu.op_pmtargetgv
= MUTABLE_GV(cSVOPx(tmpop)->op_sv);
cSVOPx(tmpop)->op_sv = NULL; /* steal it */
#endif
pm->op_pmflags |= PMf_ONCE;
tmpop = cUNOPo->op_first; /* to list (nulled) */
tmpop = ((UNOP*)tmpop)->op_first; /* to pushmark */
tmpop->op_sibling = NULL; /* don't free split */
right->op_next = tmpop->op_next; /* fix starting loc */
op_free(o); /* blow off assign */
right->op_flags &= ~OPf_WANT;
/* "I don't know and I don't care." */
return right;
}
}
else {
if (PL_modcount < RETURN_UNLIMITED_NUMBER &&
((LISTOP*)right)->op_last->op_type == OP_CONST)
{
SV *sv = ((SVOP*)((LISTOP*)right)->op_last)->op_sv;
if (SvIOK(sv) && SvIVX(sv) == 0)
sv_setiv(sv, PL_modcount+1);
}
}
}
}
return o;
}
if (!right)
right = newOP(OP_UNDEF, 0);
if (right->op_type == OP_READLINE) {
right->op_flags |= OPf_STACKED;
return newBINOP(OP_NULL, flags, op_lvalue(scalar(left), OP_SASSIGN),
scalar(right));
}
else {
o = newBINOP(OP_SASSIGN, flags,
scalar(right), op_lvalue(scalar(left), OP_SASSIGN) );
}
return o;
}
注意那个OP.
#define BASEOP \
OP* op_next; \
OP* op_sibling; \
OP* (*op_ppaddr)(pTHX); \
MADPROP_IN_BASEOP \
PADOFFSET op_targ; \
PERL_BITFIELD16 op_type:9; \
PERL_BITFIELD16 op_opt:1; \
PERL_BITFIELD16 op_latefree:1; \
PERL_BITFIELD16 op_latefreed:1; \
PERL_BITFIELD16 op_attached:1; \
PERL_BITFIELD16 op_spare:3; \
U8 op_flags; \
U8 op_private;
#endif
用来记录操作表达式。
因为我就写了一句话，后面什么也没干。
也就没什么可跟的了。
跟的过程中，可以清楚地看到，如果在lex中，没有找到什么yacc 感兴趣的东西，lex就把这些东西吞掉了。
主要就是这句：
parser->yychar = yylex();
===========
不过，perl的解释器的确是我所见过的最复杂的。
lex 会在开始前，和结束后，生成一些token，发给yacc。
这让我头大了许多。
先到这里吧。以后也不打算写了。实在累人。