本文選自：http://www.cnblogs.com/nazhizq/p/6516561.html

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一步步調試，在lparser.c文件中luaY_parser函數是語法分析的重點函數，詞法分析也是在這個過程中調用的。在這個過程中，用到一些數據結構，下面會詳細說。

Proto *luaY_parser (lua_State *L, ZIO *z, Mbuffer *buff, const char *name) {struct LexState lexstate;struct FuncState funcstate;lexstate.buff = buff;luaX_setinput(L, &lexstate, z, luaS_new(L, name));open_func(&lexstate, &funcstate);//初始化funcstatefuncstate.f->is_vararg = VARARG_ISVARARG; /* main func. is always vararg */luaX_next(&lexstate); //Luax_next用于獲取下一個字符chunk(&lexstate);//代碼塊分析check(&lexstate, TK_EOS);//判斷lua程序文件是否到達末尾close_func(&lexstate);//關閉程序lua_assert(funcstate.prev == NULL);lua_assert(funcstate.f->nups == 0);lua_assert(lexstate.fs == NULL);return funcstate.f; }

好，不著急，一步一步來看。lua_State ，LexState ，FuncState 是啥玩意呢？

?　　lua_state是lua程序運行過程中一直存在的，并且一個運行程序只有一個lua_State實例。

struct lua_State {CommonHeader;lu_byte status;StkId top; /* first free slot in the stack */StkId base; /* base of current function */global_State *l_G;//全局狀態的指針CallInfo *ci; /* call info for current function */當前函數的調用信息const Instruction *savedpc; /* `savedpc' of current function */記錄上一個函數的pc位置StkId stack_last; /* last free slot in the stack */StkId stack; /* stack base */CallInfo *end_ci; /* points after end of ci array*/函數調用棧的棧頂CallInfo *base_ci; /* array of CallInfo's */函數調用棧的棧底int stacksize;int size_ci; /* size of array `base_ci' */unsigned short nCcalls; /* number of nested C calls */lu_byte hookmask;lu_byte allowhook;int basehookcount;int hookcount;lua_Hook hook;TValue l_gt; /* table of globals */TValue env; /* temporary place for environments */GCObject *openupval; /* list of open upvalues in this stack */GCObject *gclist;struct lua_longjmp *errorJmp; /* current error recover point */ptrdiff_t errfunc; /* current error handling function (stack index) */ };

LexState是用于存儲詞法分析時的上下文數據。

typedef struct LexState {int current; /* current character (charint) */指向下一個要讀取的字符int linenumber; /* input line counter */行號int lastline; /* line of last token `consumed' */Token t; /* current token */Token lookahead; /* look ahead token */ 預讀的下一個tokenstruct FuncState *fs; /* `FuncState' is private to the parser */函數狀態的數據結構struct lua_State *L;ZIO *z; /* input stream */ 輸入流Mbuffer *buff; /* buffer for tokens */ 臨時緩沖區TString *source; /* current source name */ 源文件名char decpoint; /* locale decimal point */ } LexState; FuncState是用于存儲函數狀態的數據結構。 typedef struct FuncState {Proto *f; /* current function header */函數頭信息Table *h; /* table to find (and reuse) elements in `k' */struct FuncState *prev; /* enclosing function */指向函數鏈表的上一個函數struct LexState *ls; /* lexical state */struct lua_State *L; /* copy of the Lua state */struct BlockCnt *bl; /* chain of current blocks */int pc; /* next position to code (equivalent to `ncode') */int lasttarget; /* `pc' of last `jump target' */int jpc; /* list of pending jumps to `pc' */int freereg; /* first free register */int nk; /* number of elements in `k' */int np; /* number of elements in `p' */short nlocvars; /* number of elements in `locvars' */local變量個數lu_byte nactvar; /* number of active local variables */upvaldesc upvalues[LUAI_MAXUPVALUES]; /* upvalues */unsigned short actvar[LUAI_MAXVARS]; /* declared-variable stack */ } FuncState; 初始化完成后，就要進行詞法分析，即讀取下一個token，調用luaX_next(&lexstate); 下面進入llex.c文件的源代碼中 void luaX_next (LexState *ls) {ls->lastline = ls->linenumber;if (ls->lookahead.token != TK_EOS) { /* is there a look-ahead token? */ls->t = ls->lookahead; /* use this one */ls->lookahead.token = TK_EOS; /* and discharge it */}elsels->t.token = llex(ls, &ls->t.seminfo); /* read next token */調用llex函數讀取下一個token }

llex函數：里面是一大串的switch...case...語句，對各種可能的情況進行處理，正常的變量名或者保留字會進入default語句，分別處理空格，數字或者變量名。

for (;;) {switch (ls->current) {case '\n':case '\r': case '-': case '[': case '=': case '<': case '>': case '~': case '"':case '\'': case '.': case EOZ:default: {if (isspace(ls->current)) {lua_assert(!currIsNewline(ls));next(ls);continue;}else if (isdigit(ls->current)) {read_numeral(ls, seminfo);return TK_NUMBER;}else if (isalpha(ls->current) || ls->current == '_') {/* identifier or reserved word */TString *ts;do {save_and_next(ls);} while (isalnum(ls->current) || ls->current == '_');ts = luaX_newstring(ls, luaZ_buffer(ls->buff),luaZ_bufflen(ls->buff));if (ts->tsv.reserved > 0) /* reserved word? */return ts->tsv.reserved - 1 + FIRST_RESERVED;else {seminfo->ts = ts;return TK_NAME;}}else {int c = ls->current;next(ls);return c; /* single-char tokens (+ - / ...) */}}}}

luaX_newstring用于生成變量名，如果全局變量表中沒有該變量的字符串，則會創建新的變量字符串。對每個token，如果是保留字段，都會預先加載在全局變量表中，因此，如果不是保留字段，就會生成TK_NAME。保留字段的判定來自于if (ts->tsv.reserved > 0)，關于Token的種類，定義在llex.h頭文件中。

獲取token字符串后，進入chunk代碼：

static void chunk (LexState *ls) {/* chunk -> { stat [`;'] } */int islast = 0;enterlevel(ls);//內嵌調用層數while (!islast && !block_follow(ls->t.token)) {//當前token既不是block的開始也不是結束islast = statement(ls);//代碼語句分析testnext(ls, ';');lua_assert(ls->fs->f->maxstacksize >= ls->fs->freereg &&ls->fs->freereg >= ls->fs->nactvar);ls->fs->freereg = ls->fs->nactvar; /* free registers */}leavelevel(ls); }

statement函數用于分析語義，里面是也是大大的switch...case...語句。如果是if, while, do, for, function等等關鍵字，都會進入相應的處理函數中，在default語句中處理賦值和函數調用的分析。

static int statement (LexState *ls) {int line = ls->linenumber; /* may be needed for error messages */switch (ls->t.token) {case TK_IF: { /* stat -> ifstat */ifstat(ls, line);return 0;}case TK_WHILE: { /* stat -> whilestat */whilestat(ls, line);return 0;}case TK_DO: { /* stat -> DO block END */luaX_next(ls); /* skip DO */block(ls);check_match(ls, TK_END, TK_DO, line);return 0;}case TK_FOR: { /* stat -> forstat */forstat(ls, line);return 0;}case TK_REPEAT: { /* stat -> repeatstat */repeatstat(ls, line);return 0;}case TK_FUNCTION: {funcstat(ls, line); /* stat -> funcstat */return 0;}case TK_LOCAL: { /* stat -> localstat */luaX_next(ls); /* skip LOCAL */if (testnext(ls, TK_FUNCTION)) /* local function? */localfunc(ls);elselocalstat(ls);return 0;}case TK_RETURN: { /* stat -> retstat */retstat(ls);return 1; /* must be last statement */}case TK_BREAK: { /* stat -> breakstat */luaX_next(ls); /* skip BREAK */breakstat(ls);return 1; /* must be last statement */}default: {exprstat(ls);return 0; /* to avoid warnings */}} }

語句中的表達式通過exprstat(ls)函數處理，還有lua代碼指令的生成，有時間再寫。

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