PERL原码分析2

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继续：

int Perl_yyparse (pTHX_ int gramtype){

----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：

/* A bare statement, lacking label and other aspects of state op */
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; /* beginning of most recently read line */

-------------------------

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：

/* Binary operators between terms */
termbinop:   term ASSIGNOP term                     /* $x = $y */
           { $$ = newASSIGNOP(OPf_STACKED, $1, IVAL($2), $3);
              TOKEN_GETMAD($2,$$,'o');
           }

在核心的op.c中：

/*=for apidoc Am|OP *|newASSIGNOP|I32 flags|OP *left|I32 optype|OP *rightConstructs, checks, and returns an assignment op.  I<left> and I<right>supply the parameters of the assignment; they are consumed by thisfunction and become part of the constructed op tree.If I<optype> is C<OP_ANDASSIGN>, C<OP_ORASSIGN>, or C<OP_DORASSIGN>, thena suitable conditional optree is constructed.  If I<optype> is the opcodeof a binary operator, such as C<OP_BIT_OR>, then an op is constructed thatperforms 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 isconstructed.  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 bitsof C<op_private>, except that the bit with value 1 or 2 is automaticallyset 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_ITHREADSpm->op_pmreplrootu.op_pmtargetoff    = cPADOPx(tmpop)->op_padix;cPADOPx(tmpop)->op_padix = 0;/* steal it */#elsepm->op_pmreplrootu.op_pmtargetgv    = MUTABLE_GV(cSVOPx(tmpop)->op_sv);cSVOPx(tmpop)->op_sv = NULL;/* steal it */#endifpm->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。

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