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Annotation of researchv10dc/cmd/icon/src/iconx/lscan.c, revision 1.1.1.1

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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