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Annotation of researchv10dc/cmd/icon/src/iconx/lscan.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * File: lscan.c
        !             3:  *  Contents: bscan, escan
        !             4:  */
        !             5: 
        !             6: #include "../h/rt.h"
        !             7: 
        !             8: /*
        !             9:  * bscan - set &subject and &pos upon entry to a scanning expression.
        !            10:  *
        !            11:  *  Arguments are:
        !            12:  *     cargp[-2] - new value for &subject
        !            13:  *     cargp[-1] - saved value of &subject
        !            14:  *     cargp[0]  - saved value of &pos
        !            15:  */
        !            16: 
        !            17: #define newsubj (cargp[-2])
        !            18: #define savsubj (cargp[-1])
        !            19: #define savpos (cargp[0])
        !            20: 
        !            21: LibDcl(bscan,2,"?")
        !            22:    {
        !            23:    char sbuf[MaxCvtLen];
        !            24:    extern char *alcstr();
        !            25:    struct descrip tsubject;
        !            26: 
        !            27:    /*
        !            28:     * Make a copy of the value for &subject and convert it to a string.
        !            29:     */
        !            30:    tsubject = newsubj;
        !            31:    DeRef(tsubject);
        !            32:    switch (cvstr(&tsubject, sbuf)) {
        !            33:       case NULL:
        !            34:         runerr(103, &tsubject);
        !            35: 
        !            36:       case Cvt:
        !            37:         /*
        !            38:          * The new value for &subject wasn't a string.  Allocate the
        !            39:          *  new value and fall through.
        !            40:          */
        !            41:         strreq(StrLen(tsubject));
        !            42:         StrLoc(tsubject) = alcstr(StrLoc(tsubject), StrLen(tsubject));
        !            43: 
        !            44:       case NoCvt:
        !            45:         /*
        !            46:          * Establish a new &subject value and set &pos to 1.
        !            47:          */
        !            48:         k_subject = tsubject;
        !            49:         k_pos = 1;
        !            50:       }
        !            51:    Suspend;
        !            52: 
        !            53:    /*
        !            54:     * bscan has been resumed. Restore the old &subject and &pos values
        !            55:     *  and fail.
        !            56:     */
        !            57:    k_subject = savsubj;
        !            58:    k_pos = IntVal(savpos);
        !            59:    Fail;
        !            60:    }
        !            61: 
        !            62: 
        !            63: /*
        !            64:  * escan - restore &subject and &pos at the end of a scanning expression.
        !            65:  *
        !            66:  *  Arguments:
        !            67:  *    Arg0 - value being scanned
        !            68:  *    Arg1 - old value of &subject
        !            69:  *    Arg2 - old value of &pos
        !            70:  *    Arg3 - result of the scanning expression
        !            71:  *
        !            72:  * The result of the scanning expression is dereferenced if it refers to &subject
        !            73:  *  or &pos, then copied to the first argument (the last three will
        !            74:  *  be popped when escan returns).  Then the previous values of &subject
        !            75:  *  and &pos are restored.
        !            76:  *
        !            77:  * Escan suspends once it has restored the old &subject; on failure
        !            78:  *  the new &subject and &pos are "unrestored", and the failure is
        !            79:  *  propagated into the using clause.
        !            80:  */
        !            81: 
        !            82: LibDcl(escan,3,"escan")
        !            83:    {
        !            84:    struct descrip tmp;
        !            85: 
        !            86:    /*
        !            87:     * If the result of the scanning expression is &subject or &pos,
        !            88:     *  it is dereferenced.
        !            89:     */
        !            90:    if (((word)BlkLoc(Arg3) == (word)&tvky_sub) || ((word)BlkLoc(Arg3) == (word)&tvky_pos))
        !            91:       DeRef(Arg3);
        !            92: 
        !            93:    /*
        !            94:     * Copy the result of the scanning expression into Arg0, which will
        !            95:     *  be the result of the scan.
        !            96:     */
        !            97:    Arg0 = Arg3;
        !            98: 
        !            99:    /*
        !           100:     * Swap new and old values of &subject, leaving the new value in Arg1.
        !           101:     */
        !           102:    tmp = k_subject;
        !           103:    k_subject = Arg1;
        !           104:    Arg1 = tmp;
        !           105: 
        !           106:    /*
        !           107:     * Swap new and old values of &pos, leaving the new value in Arg2.
        !           108:     */
        !           109:    tmp = Arg2;
        !           110:    IntVal(Arg2) = k_pos;
        !           111:    k_pos = IntVal(tmp);
        !           112: 
        !           113:    /*
        !           114:     * Suspend the value of the scanning expression.
        !           115:     */
        !           116:    Suspend;
        !           117: 
        !           118:    /*
        !           119:     * Upon resumption, restore the new values for &subject and &pos
        !           120:     *  and fail.
        !           121:     */
        !           122:    k_subject = Arg1;
        !           123:    k_pos = IntVal(Arg2);
        !           124: 
        !           125:    Fail;
        !           126:    }

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